| Absorbance Units Full Scale (AUFS) |
A term used to describe the sensitivity setting of an ultraviolet detector. |
| Accelerator Mass Spectrometry (AMS) |
The nuclei of ions generated in an ionization chamber are accelerated to a MeV or greater level and used to bombard a target gas or thin metallic film. The samples are dissociated down to ions such as 12C, 13C, and 14C and mass analysis is then performed. The method is used for dating of samples and in other areas. |
| Adduction |
Ion type B+ or B- is added to neutral molecule M to create an [M+B]+ ion or [M+B]- molecule. (e.g. [M+NH4]+, [M+Na]+, [M+Cl]-). |
| Adiabatic Ionization |
This is the addition or removal of electrons from atoms or molecules to create ions in the ground state. |
| Affinity Chromatography |
A type of chromatography in which an adsorbent is used which contains a biospecific ligand, e.g., an enzyme, antibody, protein, connected to a solid support via a functional group on the support. The column, packed with such a material, exhibits specific affinity for a bio-active molecule. |
| Alpha |
A measure of chromatographic selectivity or relative retention; a separation factor between two chromatographic peaks. It is actually the ratio of the capacity factors (k') for the two peaks. |
| Analyte |
This is another expression for the term 'sample'. Used in FAB and ESI to designate samples dissolved in solvent matrices. (e.g., The analyte molecules are in solution.) |
| Analyzer |
The section of a mass spectrometer where ion masses are separated and various focusing operations are done. |
| Analyzer Tube |
This designates the tube in mass spectrometers through which ions pass. |
| Appearance Energy (AE) |
The minimum energy that must be supplied to atoms or molecules to produce a certain ion (molecular ion, multiply charged ion, fragment ion, etc.). The term appearance potential is not used in this conjunction. |
| Associative Ionization |
Describes the creation of single ions or associative ions through the internal energy from mutual interactions between neutral excited atoms A* or excited molecules M*. Chemi-ionization has the same meaning. |
| Atmospheric Pressure Chemical Ionization (APCI) |
This is one method of ionization under atmospheric pressure. Normally designates ionization of vapor droplets, generated by spraying at atmospheric pressure, through reactions with ions (reagent gas ions) generated by corona discharge or other methods. |
| Atmospheric Pressure Ionization (API) |
General term for ionization done under atmospheric pressure. (e.g., APCI, ESI, ISP, APS, LI) . |
| Atmospheric Pressure Spray (APS) |
This term describes the spraying of sample solution under atmospheric pressure, from the end of an LC capillary tube using heating, pressurized gas flow, ultrasound, etc. Since ionization occurs simultaneously with spraying the term is also used to mean spray ionization. |
| Atomic Mass Unit (amu) |
The unit is defined as 1/12 the mass of a single 12C atom and is equal to 1.6605655 x 10-27kg. The unit, u, is used to express atomic and molecular weights |
| Atomic Secondary Ion Mass Spectrometry (Atomic SIMS) |
Describes SIMS of samples with solid atoms such as metals, carbon, silicon, etc. |
| Atomic Unit (AU) |
A unit system for creating length, time and energy using basic units of electron mass me, electron charge e and Planck's constant divided by 2π. AU is the symbol used. |
| Atomic Weight |
The mass of any element, expressed in grams, when the number of atoms present (Avogadro's number) is equal to the number of atoms in 12g of 12C carbon (1mol). The atomic weight of an element is an average value and is determined by measuring the mass and relative proportion of isotopes of the element using a mass spectrograph. |
| Auto-ionization |
Describes the spontaneous ejection of an electron by a previously excited atom A* or molecule M* to create an ion. M* → M+• + e- |
| Average Molecular Weight |
Same meaning as molecular weight |
| Axial Diffusion |
Also known as Longitudinal Diffusion. Natural diffusion of the sample component solute band in the mobile phase, caused by the concentration gradient. The longer a compound solute band stays on the column, the greater the longitudinal diffusion. |
| Background Mass Spectrum |
This is the mass spectrum, obtained when no sample is present; it is the spectrum of residual materials in the ionization chamber. |
| Base Peak |
Peak used as the basis for determining relative ion peak strengths on a spectrum. Normally the peak with the greatest intensity is selected. |
| Baseline |
Constant signal produced by the background level of the instrument. |
| Beam Monitor (BM) |
An electrode or structure that receives a portion of an ion beam in order to measure the ion flow rate before the beam enters the analyzer section. This ion flow rate is proportional to the overall ion quantity and the beam monitor is one method for total ion detection. |
| Biological Mass Spectrometry (BMS) |
The field of mass spectrometry dealing with organic materials derived from biological systems. The spectrometry is different from organic mass spectrometry in that organic molecules are analyzed from the standpoint of biological function and the life sciences. |
| Capacity Factor (k') |
The number of column void volumes of mobile phase which must pass through a column to elute a given sample component. It is a measure of the tendency of the sample component to be in the stationary phase rather than the mobile phase. |
| Carrier |
Mobile phase or solvent. |
| Channel |
A void which is present in a packed column, often located near the wall of the column. |
| Charge Inversion Reaction |
Describes the bombardment of ion M+ or M- by target gas X or other material to invert the charge to M- or M+ respectively. M+ + X → M- + X2+ |
| Charge Number |
This is the total charge q of an ion divided by the elementary electric charge e. The value is an integer and is expressed as z. z = q/e. |
| Charge Transfer Reaction |
Equivalent to charge-exchange ionization. |
| Charge-Exchange Ionization (CEI) |
Also called the charge-transfer reaction. Describes an ion-molecule reaction wherein an electron moves between an ion R+• and a sample molecule M without dissociation. This is one form of chemical ionization. R+• + M → R + M+ |
| Charge-Remote Fragmentation |
In various types of generated molecular ions (M+•, [M+H]+, [M-H]-, [M+Na]+, etc.), this term describes chemical bond breakage occurring at locations apparently far removed from the charge or unpaired electron. Since molecular structure information is often reflected in CID spectra and other results, the charge-remote fragmentation concept is often used in structural analysis. Since bond breakage generally occurs through the introduction of charge or unpaired electrons, normally bonds near charges and un-paired electrons are broken. |
| Charge-Stripping Reaction |
Generally describes a type of ionization reaction wherein molecular ion Mz+, with charge number z, is bombarded by a noble gas X or some other material to eject another electron and form the ion M(z+1)+• Mz+ + X → M(z+1)+ + X + e- |
| Charge-Transfer Complex (CT Complex) |
Molecular compound generated by the resonant stabilization caused by electron interactions between an electron donor D and an electron acceptor A. D + A → D+A- |
| Chemi-ionization |
Ionization reactions that occur between neutral atoms, radicals, and - or molecules. This term has the same meaning as associative ionization. |
| Chemical Ionization (CI) |
This is the process of generating new ions through reactions between reagent gas ion RH+(reaction ion) and sample molecule M. Transfers of protons, hydrides and electrons occur as well as ion addition and other reactions. M + RH+ → [M+]+ + R M + RH+ → [M-H]- + RH2 |
| Chromatogram |
A chart recording of the chromatographic separation. |
| Cleavage |
The breaking of bonds. Cleavage can be further categorized into radical cleavage (homolytic cleavage) and ion cleavage (heterolytic cleavage). In the reaction diagram, homolytic cleavage is expressed by a one-way arrow and heterolytic cleavage is expressed by a two-way arrow. |
| Cluster |
A group of 2 or more molecules M or atoms A bonded together into Mn or An (n ≥ 2). While molecules are microscopic and materials are macroscopic, clusters are in the middle and are called mesoscopic-sized systems. |
| Cluster Ion |
The ionic form of a cluster. (e.g. Mn+•, Mn-•, [Mn+H]+, [Mn-H]-) |
| Coefficient of Variation |
Measures the size of the standard deviation relative to the size of the mean. (see the Formula) |
| Collector Slit |
Slit installed to allow only those mass separated ions with a specific m/z into the detector system. |
| Collision Activated Dissociation (CAD) |
Same meaning as collision-induced dissociation. |
| Collision Cell |
Chamber in the analysis tube where accelerated ions and target gases collide in CID experiments. |
| Collision Chamber |
Same meaning as collision cell. |
| Collision-Induced Dissociation (CID) |
Fragmentation of flying ions caused by collisional activation. |
| Collisional Activation |
Describes the result when flying ions with a certain kinetic energy collide with a target gas or other material and a portion of the kinetic energy is converted to internal energy. The resulting ions are electronically, vibrationally and rotationally excited. |
| Collisional Excitation |
Same meaning as collisional activation. |
| Column |
Chromatographic column; the tubular container that holds the chromatographic packing. Usually stainless steel tube with polished inner surface and end fittings at both ends densely packed with small porous adsorbent particles. |
| Column Volume |
The volume of the column which is not occupied by the packing material. It is often called the void volume. |
| Complex Ion |
These ions bond different types of atoms or molecules. Although these are primarily used in mass spectrometry with spark ion sources, they are also used in adduct ion, proton bound dimer, and other situations supported by non-covalent bonds. |
| Conductivity Detector |
HPLC device for continuous monitoring of effluent conductivity. Usually used with ion chromatography. |
| Corona Discharge |
Gas discharge occurring at the surface around the end of an electrode needle where the electric field intensity is high compared to the surroundings. It ionizes the reagent gas in APCI. |
| Dalton (Da) |
Mass unit for atoms and molecules One Dalton is equal to 1/12 of the mass of a single 12C atom or 1.6605655 x 10-27. It is equivalent to the atomic or molecular weight. (e.g., 1,000Da, 1 kDa) |
| Daughter Ion |
Ion generated by the cleavage of a specific parent ion. Although all fragment ions are product ions of specific parent ions, not all product ions are fragment ions. Refer to the fragment ion definition. |
| De-protonated Molecule |
Negative ions [M-H]-0 generated when neutral molecule M loses a proton H+. Typically observed during negative ion measurement with FAB or ESI. |
| Debye Length |
The distance of Coulomb's force radius, in plasmas or strong electrolyte solutions, at which a certain ion type can be reached through the surrounding ion cloud of opposing charge. Also called the ion cloud thickness. |
| Debye Radius |
Same meaning as Debye length. |
| Degassing |
The process of removing dissolved gas from the mobile phase before or during use. Dissolved gas may come out of solution in the detector cell and cause baseline spikes and noise. Dissolved air can affect electrochemical detectors (by reaction) or fluorescence detectors (by quenching). |
| Degree of Freedom |
Number of independent variables determining atomic positions in multiple atomic systems. In a system with N number of atoms, the degree of freedom would be 3N. The freedom is divided into directional, rotational and vibrational movement. The degree of vibrational freedom affects the internal energy contributing to fragmentation. With linear molecules, the degree of vibrational freedom is 3N-5 and with nonlinear molecules, the freedom is 3N-6. |
| Derrick Shift |
When accelerated precursor ions collide with target gas in CID experiments using MIKES, a portion of the kinetic energy is converted to internal energy in the precursor ions and target gas. As a result, the kinetic energy drops and peak shapes and positions on a CID spectrum shift. This is called Derrick shift. |
| Desorption Chemical Ionization (DCI) |
Ionization method, used for in-beam chemical ionization, where sample is vaporized (desorption) by strong heating of the sample spreading probe. |
| Desorption Electron Ionization (DEI) |
Ionization method, used for in-beam electron ionization, where sample is vaporized (desorption) by strong heating of the sample spreading probe. |
| Desorption Ionization (DI) |
These are ionization methods where sample compounds, in condensation phases, are desorbed as ions directly from the condensation phase without vaporization. (e.g., FD, FAB, PD, LD, MALDI) |
| Detection Limit |
The smallest amount of a substance that a detector can reliably detect during a chromatographic run. |
| Diffusion Pump |
A vacuum pump that uses oil or mercury vapor to maintain gas molecule diffusion in a single direction. Although these pumps can generally purge to a level of 10-5 ~ 10-8 Torr, a supplemental pump capable of purging to a level of 10-2 Torr is required. |
| Dimeric Ion |
Ion [M2]+ generated in the gas phase either by ionization of the dimer M2 or addition of molecule M to molecular ion M+ |
| Direct Inlet (DI) |
One method of introducing sample into the ionization chamber. Liquid or solid samples are packed in a glass tube or other holder and placed very close to the electron beam or reagent gas ions in the ionization chamber. |
| Direction Focusing |
Focusing of an ion flow on a single point. This ion flow contains ions accelerated and emitted from a single point, with the same m/z and kinetic energy, and with only slightly differing directions. Normally a single magnetic sector is used for this purpose. |
| Discharge Ionization |
Ionization method utilizing discharge phenomena in low and high-pressure gases (glow, ark, fire, corona, and spark). Vacuum discharge research, represented by glow, contributed to the beginning of mass spectrometry along with the discovery of electrons and ions in the 19th century. |
| Dispersion Forces |
A measure of the ability of a molecule to polarize another molecule. |
| Distonic Cation |
Radical cations, such as M+• or m+•, created from positive charges and unpaired electrons and with structures positioning the charge and unpaired electrons in separate positions. |
| Distribution Coefficient |
The ratio of the concentration of a given sample component in the stationary phase to its concentration in the mobile phase. |
| Double-Focusing Mass Spectrometer |
Mass spectrometer that focuses both the velocity and the speed of flying ions. Normally electric and magnetic fields are used for the focusing. |
| Dry-Packed Column |
A column which has been filled with packing material in the dry state, i.e., without the use of a solvent. Packing material is added to the column, in small quantities, while vibrating the column to encourage settling of the packing material, until the column is completely filled. |
| Dynamic Secondary Ion Mass Spectrometry (DSIMS) |
SIMS analysis with primary ion current density (corresponding to SIMS gun flux) of several µA/cm2 or more. Primarily used in component analysis of sample surface layers in the depth direction. |
| Efficiency |
The ability of a chromatographic system (primarily the column) not to cause spreading of a chromatographic peak (band). The efficiency is often measured in terms of 'number of theoretical plates. |
| Electric Sector |
Pair of electrode plates arranged in concentric circles for focusing the kinetic energy of flying ions. This sector is used in double-focusing mass spectrometers and flight time mass spectrometers. |
| Electrohydrodynamic Ionization (EHI or EHDI) |
Ionization method where an electrolyte solution of sodium iodide, ammonium acetate, or other material dissolved in glycerin is sprayed from the end of a metallic capillary tube with a high electric field (~10kV) applied. Spray ionization then occurs while tearing off ions by an opposing electrode. The sodium ions and multi-protonated glycerin cluster ions thus generated can be used as impact particles for MCI. When sample is dissolved in the solution ions such as [M + H]+ and [M + Na]+ are generated. |
| Electrohydrodynamics |
This scientific field deals with fluid systems where Coulomb's force has an essential role, such as the charge-separation phenomenon. |
| Electron Accelerating Voltage |
Voltage applied to accelerate electrons. |
| Electron Affinity (EA) |
The minimum energy required to remove an electron with zero kinetic energy and zero potential energy from the negative ion A•- or M•- of an atom or molecule in the ground state (electronic, vibrational, and rotational). |
| Electron Attachment |
Process where an external electron is brought into resonance in an atomic or molecular orbit to form a negative ion M•- or other compound. |
| Electron Capture Chemical Ionization (ECCI) |
Method for generating primarily negative ions through interactions between low energy electrons generated at CI ion sources and sample molecules. |
| Electron Energy |
The potential difference used to accelerate electrons used for electron beam ionization or other purposes. Corresponds to the kinetic energy of accelerated electrons obtained from the potential difference. |
| Electron Ionization (EI) |
Also called electron impact ionization. Since electrons are removed while interacting with the electron cloud of an atom or electron, impact is not the appropriate expression. Normally, when a beam of electrons accelerated to 70eV is directed at sample molecules, a portion of the energy is used for ionization by exciting and ejecting electrons from molecules. |
| Electron Volt (eV) |
A single electron volt is the energy obtained when charged particles of elementary electric charge e are accelerated between 2 points with a potential difference of 1V in a vacuum. |
| Electrospray (ES) |
Also called static electrospray. A solution is separated by charge through a high electric field of several kV at the end of a capillary tube supplying the sample solution. The solution is then sprayed while being pulled away by Coulomb's force generated from an opposing electrode. |
| Electrospray Ionization (ESI) |
Ionization method using the technology of electrospray. When a solution previously separated by charge is sprayed, static droplets with remarkable charge balance disruptions are generated. When the solvent in these droplets is evaporated (desolvation) by a heated gas or other method, the sizes become even smaller. When the Rayleigh limit is reached, the droplets are automatically destroyed by Coulomb's repulsion force and ions are generated. One feature of this method is the ability to generate multiply charged ions by protonation or deprotonation. The method is one of the softest ionization methods available. |
| Elementary Electric Charge |
The electrical charge held by a single electron or proton. This is the smallest unit of electrical charge. Also called elementary charge and expressed as e. e = 4.803242 x 10-10 esu |
| Eluate |
The liquid which emerges from a chromatographic column during a chromatographic run. It consists of the mobile phase exclusively when there are no sample components eluting; it contains both mobile phase and sample component(s) when sample component(s) are eluting. |
| Eluent |
The mobile phase. |
| Elute |
Emergence of a sample component in the mobile phase from the column. |
| Elution Volume |
The volume of mobile phase required to cause a sample component to elute from the column. It is also known as Retention Volume, and is measured from the point of sample injection to the apex of the chromatographic peak. |
| Emitter |
Used to spread sample for ionization. Carbon or silicon resin crystals (whiskers) are grown on a metallic wire to form the emitter. These are often used as positive electrodes in FD and FI. |
| Even-Electron Ion |
Ion without unpaired electrons (radicals). |
| Exclusion Limit |
In gel permeation chromatography (GPC), the largest size molecule that is able to permeate (enter into) the pores of the column packing material. Beyond this limit, larger molecules are totally excluded from the pores of the packing. |
| Faraday Cup Collector |
Cup shaped electrode for measuring ion beams. |
| Fast-Atom Bombardment (FAB) |
This is the ionization method where a solution prepared by dissolving sample compounds in a liquid matrix, such as glycerin, is spread on a metallic target. The target is then bombarded by neutral atoms (Ar, Xe, Cs) accelerated to 2kV ~ 30kV to generate ions. The method is further categorized as solid FAB when the sample is a solid, matrix FAB when a matrix solution is used and gas-phase FAB when the sample is a gas. |
| Fast-Particle Bombardment (FPB) |
General name covering FAB and SIMS. Method for generating ions by bombarding sample with atoms, molecules, or ions accelerated to 2 ~ 30kV. |
| Field Desorption (FD) |
Method for emitting ions into the gas phase. Sample spread on an emitter is heated while a high electric field is applied. Ions are then emitted by the tunneling, ion-molecule reactions, thermal fusion effects, and other phenomenon occurring on the emitter surface and around the whisker ends. The ionization phase depends strongly on the sample material and the spread condition. |
| Field Ionization (FI) |
Generation of M+• ions by removal of electrons, primarily from gas sample molecules, using a high electric field. |
| Field-Free Region (FFR) |
Region in the flight path of ions, generated in the ionization chamber, with no electric or magnetic fields for accelerating or directing the beam. |
| First Field-Free Region (1st FFR) |
Region with no field affects through which ions, generated in the ionization chamber, pass after the acceleration field and before entering the electric and magnetic fields for mass separation. |
| Flash Desorption |
Also called rapid heating desorption. In the gasification process of organic compounds, evaporation takes priority over dissociation when the heating rate is fast. Using this phenomenon, samples are vaporized (desorption) by rapid heating then ionization is done by electron beams or other methods. |
| Flow Programming |
The procedure of varying (usually increasing) the mobile phase flow rate during a chromatographic run. This technique is generally used where the use of gradient elution is prevented due to its incompatibility with the detector. |
| Flow Rate |
Volume of mobile phase passing through the column per unit of time. Usually reported as milliliters per minute (mL/min). |
| Fluorescence Detector |
A very sensitive and selective HPLC detector which monitors analyte fluorescence. Usually equipped with two monochromators at right angles to one another. The flow cell is illuminated at one face, and compounds which are excited by that light (can fluoresce) emit light at a different wavelength. This emitted light is measured via the second monochromator using a photomultiplier. |
| Fore Pump |
Supplemental pump used to support high vacuum pumps, such as the diffusion pump, in attaining the necessary vacuum level. |
| Fourier Transformation (FT) |
Physically divides electromagnetic waves or electric signals, comprised of components with various frequencies, into sine wave components (Fourier components) with a single frequency. The transformation may also refer to expression of components in the Fourier series created from an infinite number of Fourier components. The Fourier coefficient of each component corresponds to the signal intensity. |
| Fourier-Transform Ion Cyclotron Resonance (FT-ICR) |
A high frequency electric field is applied to ions moving through a cyclotron and within a fixed magnetic field. The energy is absorbed as resonance and, when the moving radius and velocity are increased, components of the resonant excitation frequency (corresponding to the z/m value of ions) are analyzed and processed using the Fourier transformation. |
| Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS or FT-ICR/MS) |
In ICR-MS, the inductance current signal, used as the synthetic wave for separation of ions with differing m/z values, undergoes the Fourier transformation to generate a spectrum. After transformation, the Fourier components correspond to ion mass and the Fourier coefficients correspond to ion intensity. |
| Fourier-Transform Mass Spectrometry (FT-MS) |
Same meaning as FT-ICR-MS. |
| Fraction Collector |
A device for trapping (collecting) sample components which have been separated by the chromatographic column. |
| Fragment Ion |
Ions generated by fragmentation. |
| Fragment Peak |
Peaks on the mass spectrum generated by fragment ions. |
| Fragmentation |
Reaction where an ion is converted to another chemical structure or is broken down into ions with smaller masses. |
| Franck-Condon Principle |
When electron transitions (excitation, de-excitation) occur due to electron beams or photons in a molecular system, the time required for the transition is extremely short compared to vibration between atoms. Therefore, the distance between atoms may be considered constant. While the general rotational cycle of molecules is 10-11~ 10-12 sec and the vibrational cycle is 10-13 ~ 10-14 sec, electron transitions are on the order of 10-16 sec. These electron transitions are also called perpendicular transitions. |
| Fronting |
Peak distortion caused by sample overloading. The chromatographic band broadens at its front edge. |
| Gas Chromatograph Mass Spectrometer (GC/MS or GCMS) |
Single hybrid instrument combining a gas chromatograph with a mass spectrometer. |
| Gas Chromatography Mass Spectrometry (GC/MS or GCMS) |
Analysis done using the gas chromatograph mass spectrometer. |
| Gas Reservoir |
When measuring mass spectra, the reservoir is used to hold sample in a gaseous condition for introduction to the ion source. |
| Gas-Phase Basicity (GB) |
When molecules or ions in the gas phase react and bond with H+ ions, the negative value of the free energy change of the reaction (-ΔG) is expressed as a thermochemical quantity. The protonation reactions of molecules and ions have different values than proton affinity due to inclusion of chemical structure effects (entropy effect). This has an important role in the generation of multiply charged protonated ions [M+nH]n+ in ESI. |
| Gel Permeation Chromatography (GPC) |
Used to separate molecules according to differences in their effective molecular sizes in dilute solutions. GPC is often used to determine molecular weight distributions and molecular weight averages for polymeric substances. Also known as Size Exclusion Chromatography (SEC). |
| Gradient Elution |
A technique for decreasing separation time by changing mobile phase composition over time during the chromatographic separation. Gradients can be continuous or stepwise. Binary, ternary and quaternary solvent gradients are used routinely in HPLC. (see also Step Gradient and Isocratic Elution) |
| Guard Column |
A small column placed between the injector and the analytical column. Protects the analytical column against contamination by sample particulates and, perhaps, by strongly retained species. The guard column is usually packed with the same material as the analytical column and is often of the same inner diameter. It is much shorter than the analytical column, is lower in cost than the analytical column and is usually discarded when contaminated. |
| Heavy Ion Induced Desorption (HIID) |
General name for particle bombardment ionization methods using beams of high energy atoms or molecules (20 ~ 300Da) accelerated on the MeV level. |
| Height Equivalent of Theoretical Plate (HETP) |
Also called plate height, HETP is the length of the column divided by the total number of theoretical plates. This is a measurement of the amount of peak broadening of a solute as it travels through the column, and is a way of evaluating the efficiency of a column. |
| High Resolution Mass Spectrometer (HRMS) |
Mass spectrometer with resolution of 1,000 or more. |
| High Resolution Mass Spectrum (HRMS) |
Mass spectrum obtained using a high resolution mass spectrometer. Normally measured to milliatomic mass units or less. |
| High-Energy Collision |
In CID experiments such as MS/MS, this term generally describes the collision of ions with 2 ~ 4keV of kinetic energy with the target gas. Normally, the kinetic energy of ions depends on the mass spectrometer model, since it is determined by the ion acceleration voltage, and high-energy collisions are done by double focusing and flight time models. Since electron excitation and further ionization occur before ion dissociation with high-energy collisions, fragments from reorganization of ion structures are also generated and are difficult to analyze. |
| HPLC |
High Performance Liquid Chromatography. |
| Hybrid System |
A single instrument integrating other instruments with different operating principles. These instruments include combinations of various chromatographs with mass spectrographs and combinations of mass spectrographs. |
| Hydride Affinity (H-A) |
Affinity level of atoms or molecules toward hydride ions (H-) and expressed in energy units. |
| In-Beam Chemical Ionization (IBCI) |
Ionization method where solid sample is spread on a metallic wire or crystalline emitter then placed within the reagent gas ions in an ionization chamber. Thermal decomposition from container walls and other sources is avoided and ionization is realized through ion-molecule reactions. |
| In-Beam Electron Ionization (IBEI) |
Ionization method where solid sample is spread on a metallic wire or crystalline emitter then placed near or in an electron beam in an ionization chamber. Thermal decomposition from container walls and other sources is avoided during ionization. Since [M+H]+ and other ions are generated in addition to M+, multiple molecular processes, such as collisions between molecules, also occur. |
| In-Beam Method |
Method where a solid sample is placed directly in an ionization chamber then ionized by proximity to or contact with an electron beam or reagent gas ions. (e.g., IBEI, IBCI) |
| In-Source Fragmentation |
This fragmentation, used relative to the post source decay (PSD) in MALDI, occurs in the ionization chamber simultaneously with or immediately after ionization. The phenomenon is also called prompt fragmentation, which causes the fragments that appear in the mass spectra of MALDI-TOF. |
| Inductively Coupled Plasma (ICP) |
A high frequency current of 2 ~ 30MHz is applied to an inductance coil. The inductance current created by the resulting magnetic field in the coil is used to ionize Ar and other elements by an electron avalanche. This creates plasma. Sample solutions are sprayed into this plasma, which reaches 5,000 ~ 7,000K, and ionized. The system can therefore be used as an ion source for mass analysis. (e.g., ICP-MS) |
| Injector, Injection Valve |
A device (often a valve) used to introduce a specific quantity of a sample solution into the chromatographic system. |
| Internal Energy |
Energy value for atoms, molecules and ions within a certain external field. The value is obtained by subtracting the potential energy belonging to the external field and the kinetic energy from the total energy. Designates the electronic, vibrational and rotational energy that contributes to ionization of atoms and molecules and dissociation of ions. |
| Intramolecular Proton Bound Protonated Molecule |
Structure of protonated molecules [M+H]+ wherein coordinated interactions between 2 or more functional groups within the molecule insert a proton. |
| Ion |
Particle (atom or molecule) having a charge. Although this name is often attributed to M. Faraday, the name was actually given by W. Whewell (1794 - 1866). |
| Ion Accelerating Voltage |
Voltage applied to accelerate an ion. |
| Ion Atmosphere |
Designates the grouping of an ion and the surrounding ions of opposite charge in plasmas or strong electrolyte solutions. This concept is a requirement of the Debye-Huckel's theory. |
| Ion Cyclotron Resonance Mass Spectrometer (ICR-MS or ICR/MS) |
Mass spectrometry using the phenomenon of increased rotational radii. These increases occur when a high frequency electric field is applied to ions with rotational or spiral movement (cyclotron movement), in a fixed magnetic field, and the energy is absorbed by resonance. |
| Ion Exchange Chromatography |
A type of chromatography with which ionized components of a sample are separated with a chromatographic column which contains active ionic sites. |
| Ion Kinetic Energy Spectrum (IKES) |
Spectrum separating ion flow according to the kinetic energy/charge ratio. In double-focusing mass spectrometry, the electric field is normally scanned to obtain this spectrum. The result is used in detection of metastable ions. |
| Ion Source |
A part of mass spectrometer used for sample ionization. Includes the ionizing parts, ionization chamber, ion flow accelerator, focusing lens and other parts. |
| Ion Spray (IonSprayTM, IS or ISP) |
This is theoretically the same type of spray method as electrospray. However, drawing on the history of spray ionization methods with no high electric field, the focus of ionization with ion spray is placed on the spray and the high electric field is supplemental. The registered trademark of IonSprayTM is also in use. |
| Ion Trap |
Using an electric field generated by an alternating current or a magnetic field, ions are forced to move in a closed orbit (cyclotron rotational movement or 3-dimensional vibrational movement) and thereby closed within a certain space (cell). |
| Ion Trap Mass Spectrometer (ITMS) |
Mass spectrometer where ions are trapped in a vacuum space (cell) using the ion trap then driven from the cell in m/z sequence using alternating current (r.f.) voltage or the corresponding frequency. The ions driven from the cell are detected directly or after Fourier transformation of frequency components (corresponding to m/z) of the induced current. |
| Ion-Neutral Complex |
Chamber in the analysis tube where accelerated ions and target gases collide in CID experiments. |
| Ion-Pair Formation |
Ionization process where both positive and negative ions are generated. M2 → [M+H]+ + [M-H]- AX → A+ + X- |
| Ion-Pairing Chromatography |
Chromatographic separation technique for fractionating ionic samples with a reverse phase column. A substance is added to the mobile phase and to the sample solution (containing a counter-ion) which can form tightly-bound ion pairs with the ionic sample components. The ion pairs 'behave' as though they are non-ionic as they pass through the reverse phase column |
| Ion/Molecule Reaction |
Reaction where ions and molecules interact to form different chemicals or cause internal energy changes. |
| Ionic Dissociation |
Describes dissociation of an ion into a smaller ion and one or more neutral particles. |
| Ionization |
Normally designates conversion of a solid, liquid or gas sample into ions in the gas phase. Dissociation of molecules in solution to ions is also called ionization. |
| Ionization Chamber |
Location within the ion source where sample interacts with electron beams or reagent gas ions to generate sample ions. |
| Ionization Cross Section |
Measurement showing probability of ionization when atoms or molecules interact with electrons or photons. |
| Ionization Efficiency |
Proportion of ions generated relative to the number of electrons or photons used for ionization. |
| Ionization Efficiency Curve |
Curve showing relationship between ionization efficiency and the energy of electrons or photons used in the ionization. |
| Ionization Energy (IE) |
It is the energy required to remove a single electron an infinite distance from a gaseous molecule, atom or group of atoms in the ground state. |
| Ionizing Cell |
Same meaning as ionization chamber. |
| Ionizing Current |
Electron or ion current used to ionize a sample. |
| Isocratic |
Separation made with a constant composition of mobile phase. |
| Isocratic Elution |
Elution chromatography in which the mobile phase composition is maintained constant throughout the entire run (see also Gradient Elution). |
| Isotope |
Atoms with the same atomic number and differing masses. There are stable isotopes and radioactive isotopes with a certain lifespan. |
| Isotope Peak |
Peak produced by isotopic ion. |
| Isotopic ally Enriched Ions |
Ions of a molecule for which a certain element (such as C) has been enriched using a specific isotope (such as 13C). |
| Isotopic Ion |
Ions of particles containing at least 1 isotope that is not in the proportional majority. For example, in molecules consisting of C, H, and O, ions with isotopes from the proportional majority would be m+. On the other hand, ions containing a single 13C or 2H would be (M+1)+ and ions containing a single 18O would be (M+2)+ and would be called isotopic ions. |
| Isotopic Molecular Ion |
Molecular ions containing at least 1 isotope that is not in the proportional majority. For example, in molecules consisting of C, H, and O, ions with isotopes from the proportional majority would be m+. On the other hand, ions containing a single 13C or 2H would be (M+1)+ and ions containing a single 18O would be (M+2)+ and would be called isotopic ions. |
| Kinetic Energy Release (KER) |
In metastable ion decay, this term describes the conversion of a portion of internal energy to kinetic energy. The result is a broadening of the metastable peak width. A fragmentation mechanism can be debated from the shape and width of this peak. |
| Laser Desorption (LD) |
Describes the process of directing laser light at a solid sample in order to generate sample ions in the gas phase. Also called laser ablation when used to gasify solid samples. |
| Laser Desorption Ionization (LDI) |
Ionization method using laser desorption. In this case, there is no ablation. |
| Laser Ionization (LI) |
Describes the process of directing laser light at a solid sample in order to generate sample ions in the gas phase. One of the photo ionization methods. |
| LC/MS |
Liquid Chromatography/Mass Spectrometry. A liquid chromatographic analysis in which the separated sample components are passed into a mass spectrometer for detection and identification. |
| Lens Voltage |
Voltage applied to lens electrodes made of metallic plates for the purpose of focusing an ion flow. |
| Linear Velocity |
Average linear speed of the mobile phase flowing through a chromatographic column. |
| Linked Scan |
Method of holding the electric field (E) and magnetic field (B) of an analyzer constant and scanning simultaneously in mass spectrometers with 2 or more analyzers. The method is used to detect only specific ions. Scanning methods include the following. Constant B/E - Method for obtaining spectra for all product ions produced by a specific precursor ion. Constant E2/V (V - ion acceleration voltage) - Same spectrum obtained by constant B/E linked scan. Constant B2/E - Method for obtaining all precursor ions generating a specific product ion. Constant B[1-(E/E0)]1/2/E - Method for obtaining all precursor ions desorbed from a specific neutral particle. |
| Liquid Chromatograph Mass Spectrometer (LC/MS or LCMS) |
Hybrid instrument combining a liquid chromatograph with a mass spectrometer. |
| Liquid Chromatography Mass Spectrometry (LC/MS or LCMS) |
Analysis using liquid chromatograph mass spectrometer. A liquid chromatographic analysis in which the separated sample components are passed into a mass spectrometer for detection and identification. After separating a mixed sample solution using the liquid chromatograph, mass analysis is done for single components. |
| Liquid Ionization (LI) |
One atmospheric pressure ionization method. Sample dissolve in a suitable solvent is spread on a heatable metallic needle. An inert gas such as Ar is supplied and is exposed to the liquid surface. Benning ionization occurs and ions are vaporized. This is one of the softest ionization methods, combining the relatively natural liquid evaporation with Benning ionization and ion/ molecule reactions. |
| Liquid Secondary Ion Mass Spectrometry (LSIMS) |
Method for generating secondary ions of a sample. With SIMS, sample compounds are dissolved in a liquid matrix such as glycerin then spread on a metallic target plate. The plate is then bombarded by primary ions (Ar+, Xe+, Cs+) accelerated to 2 ~ 30kV and with a current density of 2 ~ 3 nA/cm2 or less. The spectra obtained are nearly equivalent to the FAB method. |
| Liquid-Liquid Partition Chromatography |
Chromatography in which both phases are liquids. |
| Liquid-Phase Basicity (LB) |
Defined as the negative value of the free energy change of a reaction when atoms or molecules in the liquid phase accept a proton from oxygen or other particles. Expresses the proton acceptance capability in liquid as an energy unit. |
| Liquid-Solid Chromatography |
Chromatography in which the stationary phase is a solid (adsorbent) and the mobile phase is a liquid. |
| Load |
The mass of sample injected into the column. |
| Longitudinal Diffusion |
Also known as Axial Diffusion. Natural diffusion of the sample component solute band in the mobile phase, caused by the concentration gradient. The longer a compound solute band stays on the column, the greater the longitudinal diffusion. |
| Low-Energy Collision |
In CID experiments such as MS/MS, this term generally describes the collision of ions with 20 ~ 30eV of kinetic energy with the target gas. Normally, the kinetic energy of ions depends on the mass spectrometer model, since it is determined by the ion acceleration voltage, and low-energy collisions are done by quadrupole models. Since vibrational excitation, which contributes to ion fragmentation, occurs before electron excitation with low-energy collisions, easy to analyze fragments that can be projected from the original ion structure, are often obtained. |
| Magnetic Deflection |
Changes (deflection) in the direction of an ion beam occurring as a result of ion movement in a magnetic field. |
| Magnetic Field Scan |
Changing the intensity of a magnetic field at a constant rate in order to measure a mass spectrum. |
| Magnetic Sector |
Fan-shaped magnetic field used in single beam mass spectrometers. The sector is used for directional focusing of an ion flow. |
| Magnetic Sector-Type Mass Spectrometer |
Mass spectrometer that separates ions according to m/z using a magnetic field. Often designates single beam mass spectrometers using a fixed magnetic sector. |
| Mass |
Basic material characteristic determining the momentum and kinetic energy of a material using the gravitational interaction between 2 bodies. The definition can include gravitational mass, inertial mass, static mass, and electromagnetic mass. The mass of atoms and molecules determined by mass analysis is inertial mass as defined by Newton's formula F = ma. |
| Mass Analyzed Ion Kinetic Energy Spectrum (MIKES) |
Designates the kinetic energy spectrum of ions with a specific mass number and corresponds to the spectra of all product ions generated from a specific precursor ion. Using a reverse double-focusing mass spectrometer with a magnetic field → electric field sequence, the precursor ions pass through a fixed magnetic field and are then scanned in the electric field to produce the spectrum. |
| Mass Chromatogram |
Chromatogram obtained by mass chromatography. |
| Mass Chromatography |
Method for producing a record of ion intensities for specific mass numbers after using a computer to record the mass spectra at fixed time intervals using GC/MS or other methods. |
| Mass Fragmentogram |
Chromatogram obtained by mass fragmentography |
| Mass Fragmentography |
Record obtained by detecting ion intensities in real time for specific mass numbers using selective ion detection with GCMS or other methods. |
| Mass Marker |
Device for calibration of ion m/z values and used in combination with Hall elements for detecting magnetic field intensities. |
| Mass Number |
Nearest integer when expressing the mass of an atom in units that define 12C as 12. The number is approximately the sum of protons and neutrons in the atomic nucleus. In mass analysis, the mass number is the sum of the masses of the atoms making up an ion or other particle (12C = 12, 1H = 1, 16O = 16, 14N = 14...). |
| Mass Spectrograph |
Mass analyzer that detects ions by direct photographic plate recording and produces an image as a result. |
| Mass Spectrometer (MS) |
Mass analyzer that detects and records ions as a current. |
| Mass Spectrometry (MS) |
Analysis method for separating ions by m/z value. The method involves application of electric or magnetic fields to gas phase ions of an atom or molecule that are sprayed or moved through a vacuum tube. |
| Mass Spectrometry/Mass Spectrometry (MS/MS) |
Also called the tandem mass analysis method. Normally, 2 mass spectrometers are connected and a specific ion (precursor ion), from among the molecular and fragment ions generated at the ion source, is selectively passed through the first instrument. Before entering the second instrument, the precursor ion is excited and dissociated through bombardment by an inert gas or other material. The ions thus generated are separated according to mass/charge in the second instrument then detected as an ion spectrum. (e.g. MS/MS-CID, MS/MS-MID spectrum) |
| Mass Spectroscope |
Instrument for measuring mass spectra. General designation for mass analyzers and mass spectrographs. |
| Mass Spectroscopy |
Expansion of photometric methods to use atoms and molecules in place of electromagnetic waves. With photometric methods the wavelength or intensity of electromagnetic waves are adjusted to study energy levels and transition probabilities of materials. Currently mass spectrometry is used. |
| Mass Spectrum |
Record of ion intensities on a bar graph in m/z sequence. |
| Mass Transfer |
The movement of material between two phases. In chromatography, it refers to the diffusion of sample molecules caused be the movement into and out of the stationary phase. |
| Mass Unit (= Unified Mass Unit) |
Expression of mass converted to energy units (eV) using mc2. The symbol is MU0. When the mass of 12C is M the result is 1MU = mc2/12 = 931.478MeV. |
| Mass-to-Charge Ratio (m/z) |
Value obtained by dividing ion mass m by charge z. |
| Massive-Cluster Impact Ionization (MCI) |
Method for generating ions by bombarding a liquid matrix sample solution spread on a metallic target plate with multiply charged cluster ions of glycerin accelerated to 10 ~ 20kV. The clusters are protonated 20 ~ 300 times, have masses of 107 or greater, and have diameters on the sub-micro level (~0.01µm). The measurement method is the same as FAB. The multiply-charged cluster ions are generated by electrohydrodynamic ionization. |
| Matrix |
Designates the base material holding the sample compound in FAB, LSIMS, MALDI and LI. Organic solvent, viscous liquids, crystals, metallic powders, or some mixture of these materials may be used depending on the purpose. Matrices fill important roles in ionization including; reagent gas proton reception; energy absorption and buffering in electron bombardment and laser illumination; and support to make repetitive and long-term measurement possible. |
| Matrix-Assisted Laser Desorption (MALD) |
One type of ionization or vaporization method. The sample is dissolved and hardened in a matrix (liquid or crystalline material, metallic powder, etc.) with absorption in the wavelength region of the laser being used. The solidified sample is then illuminated with the laser to cause vaporization or ionization. The term is also used interchangeable with MALDI. |
| Matrix-Assisted Laser Desorption Ionization (MALDI) |
Ionization method using matrix-assisted laser desorption. Since desorption and ionization occur almost simultaneously, the term is also used with the same meaning as MALD. |
| Matrix-Assisted Plasma Desorption (MAPD) |
Measurement using plasma desorption with the sample dissolved in a liquid or solid matrix. |
| Mattauch-Herzog Geometry |
Used in double-focusing mass spectrometers when the electric field and magnetic field are arranged at deflection angles of π/(4√2) and π/2 radians respectively. |
| McLafferty Rearrangement |
Designates rearrangement of hydrogen atoms, through a 6-membered ring, to a specific heteroatom. The term is also often used to describe the fragmentation that occurs simultaneously at the γ bond position of the heteroatom. |
| Mean |
The average or expected value of a set of variables. (see the Formula) |
| Membrane Inlet Mass Spectrometry (MIMS) |
Method of using polyethylene, Teflon, silicon or some other membrane when introducing sample to the ionization chamber. Sample can be selectively introduced using the transmission characteristics of the membrane (hydrophilicity, hydrophobicity, etc.) |
| Metastable Ion (MI) |
Designates ions generated in the ionization chamber that dissociate at some location in the analysis tube before reaching the collector. Normally these ions have life spans of 10-5 ~ 10-6 seconds. Dissociation of metastable ions with short life spans may be called fast metastable ion decay. |
| Metastable Ion Decay (MID) |
Designates the dissociation of metastable ions. (e.g. metastable ion decay spectrum) |
| Metastable Peak |
Peaks on the mass spectrum generated by ions created from decay of metastable ions in flight. |
| Milli-Atomic Mass Unit |
Unit equivalent to 1/1000 of the atomic mass unit (u). Also called the millimass unit. |
| Mobile Phase |
The moving liquid phase which carries sample components through a chromatographic column (see also Stationary Phase). |
| Molecular Compound |
Weak bonding between 2 or more molecules by charge transfer force, hydrogen bonds, solvation force or other weak forces. |
| Molecular Ion |
Molecules containing only majority isotopes and having lost or gained electrons without bond breakage. Normally designated as M+• or M-•. The term also denotes a type of molecular-related ion. In order to unify the symbols with multiply charged ions, represented by M2+ and M3+, the symbol is also expressed as M•+. |
| Molecular Secondary Ion Mass Spectrometry (Molecular SIMS) |
A static SIMS method for generating secondary ions of a sample. Solid molecular samples are spread on a metallic target plate. The plate is then bombarded by primary ions (Ar+•, Xe+•, Cs+•) accelerated to 2 ~ 30kV to generate secondary ions. |
| Molecular Weight (Molar Weight) |
The mass of any molecular compound, expressed in grams, when the number of atoms present (Avogadro's number) is equal to the number of atoms in 12g of 12C carbon (1mol). The molecular weight of a molecular compound is an average value and is determined by measuring the mass and proportion of isotopes of the compound using a mass spectrograph. |
| Molecular-Related Ion |
Ion type directly related to elucidation of molecular weight and generated without the breakage of internal molecular bonds except bonds related to hydrogen or proton dissociation. (e.g. [M-H]+, [M-H]-, M+•, M-•, [M+H]+, [M+Na]+, [M+Cl]-, [M+NH4]+) |
| Mono Isotopic Mass |
Mass calculated using the mass number of the most common natural isotope. The mass of molecules expressed in mono isotopic mass terms is generally smaller than the corresponding molecular mass. |
| Multi-Photon Ionization (MPI) |
Method for ejecting electrons using laser or other light. Photons are absorbed by the atom or molecule in multiple steps until the ionization energy is exceeded and the excited particle ejects an electron. |
| Multiple Collision |
This term refers to CID technology where target ions pass through the collision cell while interacting (colliding) with multiple target gases. These collisions occur more readily in the triple quadrupole mass spectrometer with its relatively long collision cell. The level of ionic dissociation (corresponding to the overall internal energy obtained through collisions) is more strongly dependent on the number of collisions than the collision energy. |
| Multiply Charged Ion |
Ion with a multiple charge value. (e.g. M3+, M3-, [M+5H]5+, [M-5H]5-) |
| Multiply De-protonated Molecule |
Designates multiply charged ions [M-nH]n+ generated when molecule M loses multiple protons H+. These are observed in peptide and protein molecules during negative ion measurement with ESI. |
| Multiply-Protonated Molecule |
Designates multiply-charged ions [M+nH]n+ generated when molecule M gains multiple protons H+. Typical multiply charged positive ions are generated during ESI measurement of peptides and proteins with multiple proton receptor positions, such as basic positions. |
| N |
Number of theoretical plates, efficiency (see Efficiency, Theoretical Plate). |
| Nanoelectrospray (nanoES) |
Electrospray technology for generating fine droplets with diameters of 200nm or less by ejecting sample solution from a capillary tube, with an internal diameter of approximately ~1µm, at a flow rate of 20 ~ 40nL/min. Consistent spectra can be obtained by supplying several µL of sample solution with concentrations of several pmol/µ to a capillary tube with 600 ~ 700V applied. |
| Negative Ion (NI) |
Ions with negative charges. Also called anions. (e.g. M-•, [M-H]-, [M+O]-) |
| Negative Ion Chemical Ionization (NICI) |
Ionization featuring electron capture by compounds having functional groups with high electrophilicity, such as halogen and nitro groups, to create M-• or oxygen added ions [M+O]-. The method provides high sensitivity analysis of negatively charged compounds. |
| Neutral Fragment Re-ionization (NfR) |
Designates ionization of neutral fragments, generated when accelerated ions are dissociated in the collision cell or other location, by further high-energy collisions. The method is useful in the detection of neutral fragments. |
| Neutralization Re-ionization Mass Spectrometry (NRMS) |
With this spectrometry method, ions generated and accelerated in the ionization chamber are neutralized in a collision chamber containing target gas. After various ion types are removed by a deflector, collision ionization is done again in another collision chamber, the particles are dissociated by CID and mass analysis is executed. Although ion yield drops to 10-3 ~ 10-5, the method is used in re-search on intermediaries of organic ions. |
| Nier-Johnson Geometry |
Used in double-focusing mass spectrometers when the electric field and magnetic field are arranged at deflection angles of π/2 and π/3 radians respectively. |
| Noise |
Random fluctuation of the chromatographic signal. |
| Nominal Mass |
Same meaning as mass number |
| Normal Phase Chromatography |
Chromatography in environments where the polarity of the stationary phase is greater than the mobile phase. |
| Odd-Electron Ion |
Same meaning as radical ion |
| Organic Mass Spectrometry (OMS) |
This term is used broadly to designate the mass spectrometry field dealing with organic compounds. The term is also used, in a narrow sense, to designate spectrometry used for structural analysis, centered on mass determination and fragmentation structures, of synthetic and natural compounds. Compared to LSIMS, since no liquid matrix is used, the damage from direct collisions is large, so, many fragment ions are generated and few molecular ions are generated. |
| Organic Secondary Ion Mass Spectrometry (Organic SIMS) |
A static SIMS method for generating secondary ions of a sample. Organic sample compounds are spread on a metallic target plate then bombarded by primary ions (Ar+, Xe+, Cs+), accelerated to 2 ~ 30kV, to generate secondary ions. Compared to LSIMS, since no liquid matrix is used, the damage from direct collisions is large and many fragment ions are generated and few molecular ions are generated. The charge-up caused by ion collisions also has a deleterious influence on measurement. |
| Packing Material |
The material which is used as the chromatographic stationary phase in the liquid chromatography column. |
| Parent Ion |
Designates the original molecular ion or fragment ion that dissociated to create further fragment ions. |
| Particle Beam (PB) |
Using a volatile solvent, sample solution is sprayed in fine droplets from the end of an LC capillary tube and solvent is removed while the spray (particle beam) passes through a heating tube. With the jet separator, solvent and other small molecules are purged and the mono-molecular beam is led into the ionization chamber for EI or CI ionization. |
| Pascal (Pa) |
Pressure unit. 1Pa = 10µbar, 133Pa = 1Torr = 1mmHg |
| Peak |
When the flow intensity of ions separated by mass is detected, amplified and recorded on a chart, the results generally take the form of mountains with each rise corresponding to an m/z value. These mountains are called peaks. With GCMS, peaks appear on the chromatogram in addition to the spectrum. (e.g. Peak height, peak intensity) |
| Peak, Chromatographic Peak |
A signal change which is the result of elution and detection of a sample component. |
| Pellicular Support |
A chromatographic solid support whose particles consist of a solid core and a porous surface. |
| Penning Ionization (PI) |
Describes ionization caused by interactions between excited neutral atoms or molecules (A• or M•) and sample molecules. The internal energy of the excited neutral particles must exceed the ionization energy of the sample molecules and the lifespan of the excited state must be longer than the interaction time. M+ A- → M+. + A + e- |
| Photo-Induced Ionization |
Designates ionization of molecules through absorption of electromagnetic wave energy (hv) when light is directed at a sample. |
| Photo-Ionization (PI) |
Same meaning as photo-induced ionization. |
| Photographic Plate Recording |
A glass plate spread with light sensitive material at which a mass separated ion flow is directed. The plate is developed in the same way as film and a picture of the mass spectrum is thus obtained |
| Plasma Desorption (PD) |
This is one method of HIID. The high energy disintegration particles of 106Tc22+ and 142Ba18+ (~100MeV) from the radioactive 252Cf nucleus are directed at the back of a thin metal sheet or cellulose membrane spread with sample. Various ions are then created by desorption. |
| Polarity Index |
A classification of solvents according to their effective polarities (solvent strengths) in adsorption chromatography. |
| Positive Ion (PI) |
Ions with positive charges. Also called cations. (e.g. M+•, [M+H]+, [M+Na]+) |
| Post Source Decay (PSD) |
With MALDI, this term designates the phenomenon occurring when the excessive internal energy of ions themselves or collisions with free gas cause dissociation immediately after the ions generated by laser illumination exit the high speed field region. This term corresponds to metastable dissociation. Ions decay after leaving the ion source but before reaching the collector. |
| Precursor Ion |
Designates the original ion present before other ions or neutral particles were formed. The term is more widely used than parent ion. |
| Predissociation |
Describes a photo dissociation mechanism of molecules. When molecule M, in the ground state, absorbs electron or photon energy to enter the excited state of M- or (M+•)-. Dissociation occurs before the molecule can return to the electronic ground state through energy distribution. The lifespan of the excited state is on the 10-12 ~ 10-13 second level and the oscillation cycle is long at 10-13 ~ 10-14 seconds. These molecular ions, however, cannot be observed with mass spectrometers. |
| Principle Ion |
Molecular or fragment ions containing only principle isotopes. |
| Principle Isotope |
The isotope of any given element with the highest relative abundance. |
| Product Ion |
Ion generated from the fragmentation reaction of some specific ion. The original specific ion is called the precursor ion. (e.g. Product ion spectrum) |
| Proton Acceptor |
When protons move between molecules or molecular ions to create protonated molecules or multiply charged protonated molecules, the particle receiving the proton is called the proton acceptor. Br φ nsted bases are proton acceptors. |
| Proton Affinity (PA) |
Designates the heat of reaction (DH) for a protonation reaction. Expresses the ease with which a proton can be removed from a molecule or ion in energy units. The proton affinity of molecule M would be expressed as PA(M). |
| Proton Bound Dimer |
Dimer ion made by 2 molecules of the same or different type holding a proton in between. If the molecules are M1 and M2 the dimer ion would be M1...H+...M2. |
| Proton Donor |
When protons move between molecules or molecular ions to create protonated molecules or multiply charged protonated molecules, the particle giving the proton is called the proton acceptor. In proton movement between molecules the proton donor is the de-protonated molecule [M-H]-. Br φ nstead acids are proton donors. |
| Protonated Molecule |
Ion [M+H]+ generated when a proton H+ is added to molecule M. |
| Pulse Damper |
A device which is used to minimize or remove pump pulsations from the mobile phase flow. |
| Quadrupole Mass Spectrometer (QMS) |
A type of mass spectrometer for separating ions by mass/charge using a quadrupole magnetic field. The field is created by applying a voltage, combining direct current and high frequency, to quadrupole rods with hyperbolic curves or equivalent cross sections. |
| Quasi-Equilibrium Theory (QET) |
One theory for predicting fragmentation of molecular ions in the excited state. The internal energy of a molecule in the excited state (electronic, vibrational, rotational) is statistically distributed to various oscillators and bond breakage is assumed to occur due to vibration excitation alone. This is also called the statistical theory and is essentially the same as the independently developed RRKM theory. |
| Quasi-Molecular Ion |
Designates protonated [M+H]+ and deprotonated [M-H]- molecules. These are a type of molecule related ion. |
| Radical Ion |
Designates ions having unpaired electrons (radicals). Normally the radical symbol (dot) is placed to the right of the charge as in M+• and M-•. However, in inorganic and organic chemistry literature the dot is sometimes placed before the charge as in M•+ and M•-. |
| Radio Frequency Spark |
Discharge caused by 23 ~ 30 kV with high frequencies of 200 kHz or more. |
| Rayleigh Limit |
Limiting droplet size at which self-fragmentation will occur with static charge droplets generated in ESI or other ionization processes. Self-fragmentation occurs when the Coulombic repulsion force generated by the excess charge in a droplet exceeds the surface tension maintaining the droplet. Vaporization of electrons and ions from the static charge droplet surface occurs even with droplets having large sizes. As the size becomes even smaller, the surface tension begins to squeeze the droplet and promote further vaporization. |
| Reactant Ion |
In chemical ionization, this term designates ions generated from the reagent gas that directly contribute to ionization of the sample molecules. (e.g. CH5+, NH4+, t-C4H9+) |
| Reagent Gas |
In chemical ionization, this term designates the gas used to ionize the sample molecules. (e.g. CH4, NH3, i-C4H10) |
| Reagent Gas Ion |
Same meaning as reactant ion. |
| Rearrangement Ion |
Ions generated by the fragmentation accompanying rearrangement of atoms or atomic groups. |
| Rearrangement Reaction |
Designates fragmentation reactions that create rearrangement ions. (e.g. McLafferty rearrangement reaction) |
| Reciprocating Piston Pump |
The most common HPLC pump design. A single or multiple-piston design forces mobile phase through the column on a forward piston stroke, and refills the cylinder with mobile phase on the recycle stroke. |
| Reconstructed Ion Chromatogram |
Designates a chromatogram drawn after some processing of mass spectra or other data recorded in a computer. |
| Refractive Index Detector |
HPLC detector which monitors the changes of the refractive index of the column effluent. The only universal detector in HPLC, and the least sensitive one. |
| Relative Abundance |
Different expression for relative intensity. |
| Relative Intensity |
In mass spectrometry this term designates the ratio between the intensity of the ion beam for a certain mass and the maximum intensity of the ion beam. Normally this ratio is expressed using the heights of each peak on a spectrum with the highest peak defined as 100. Another method defines the total ion quantity or the ion quantity in a specific region as 100. The peak height method is also called the pattern coefficient while the ion quantity method is called the %Σ method. Ion peak intensity terms for ion quantity (abundance), ion peak strength (intensity), peak height (height) and peak surface area (area) are also used. |
| Relative Molecular Mass |
Same meaning as molecular weight. The symbol Mr is used. |
| Relative Sensitivity Coefficient |
With spark ion source mass spectrometry, this term refers to the relative intensity of spectral lines for each element when the spectral line of a certain element is defined as the standard (1.00). |
| Repeller Voltage |
The voltage applied to an electrode to push generated ions from the ion chamber toward the analyzer. |
| Resolution |
Separation of a chromatographic band (peak) from an adjacent one. |
| Resolving Power |
Same meaning as resolution. |
| Retention Volume |
The volume of mobile phase required to cause a sample component to elute from the column. It is also known as elution volume, and is measured from the point of sample injection to the apex of the chromatographic peak. |
| Retention Volume, Adjusted |
The actual retention volume less the void volume. |
| Reverse Phase Chromatography |
Chromatography in environments where the polarity of the stationary phase is greater than the mobile phase. |
| Rice, Ramsperger, Kassel and Marcus theory (RRKM theory) |
One theory for predicting fragmentation of molecular ions in the excited state. Essentially the same as Quasi-equilibrium theory. |
| Run |
A complete chromatographic separation process, from the point of sample introduction to the point of detection (or, for preparative chromatography, to the point of collection) of all of the sample components. |
| Scanning |
The process of sequentially changing the magnetic or electric field strength in a single direction in order to measure mass spectra or other data. |
| Scrambling |
Free interchange of a specific number of atoms at a location on an ion or molecule. |
| Second Field-Free Region (2nd FFR) |
Normally, in double-focusing mass spectrometers consisting of electric and magnetic fields, this term refers to a position with no field and through which ions pass. The position is located after the electric (or magnetic) field, through which ions generated in the ionization chamber pass for mass separation after acceleration, and before the magnetic (or electric) field. |
| Secondary Electron Multiplier |
Describes a special electron tube for amplifying minute ionic currents using the secondary electron emission phenomenon from metallic surfaces or other specially processed materials. |
| Secondary Ion Mass Spectrometry (SIMS) |
Mass spectrometry method for analyzing secondary ions emitted when Ar+ or other ion beams (primary ions) are directed at a sample. Normally this method is used in surface analysis (element analysis) of solid samples such as semiconductors. |
| Secondary Neutral Mass Spectrometry (SNMS) |
Mass spectrometry method using ionization, by laser or other method, of neutral particles emitted from a sample surface in FAB, SIMS or other process. One surface analysis method used for semiconductor materials and other samples. |
| Selected Ion Detection (SID) |
Continuous detection of ions with a specific mass number. |
| Selected Ion Monitoring (SIM) |
Same meaning as selected ion detection. |
| Selectivity |
Also known as Alpha. A measure of chromatographic selectivity or relative retention; a separation factor between two chromatographic peaks. It is actually the ratio of the capacity factors (k') for the two peaks. |
| Separator |
With GCMS, this part is placed between the column and ion source in order to separate and remove a large portion of the carrier gas, concentrate the sample, and then introduce the sample to the ion source. |
| Sequential Analysis |
The technique whereby a sample is fractionated first by one mode of chromatography, followed by a second, different mode. Sometimes, part of the sample is removed following the first mode, and the remaining components subjected to the second mode. Sequential analysis is used for samples which contain many components with widely diverging chromatographic properties. |
| Simple Cleavage |
Reaction where a single bond is broken to form 2 fragments. |
| Single Collision |
This term refers to CID technology where target ions pass through the collision cell while interacting (colliding) with a single target gas. The collisions occur more readily in the double-focusing mass spectrometer with its relatively short collision cell. |
| Single Filament Method |
One surface ionization method wherein a single filament is used to vaporize and ionize the sample. |
| Single-Focusing Mass Spectrometer |
Mass spectrometer that only does directional focusing of ions. Normally a constant, fan-shaped, magnetic field is used. |
| Size Exclusion Chromatography (SEC) |
Used to separate molecules according to differences in their effective molecular sizes in dilute solutions. SEC is often used to determine molecular weight distributions and molecular weight averages for polymeric substances. Also known as Gel Permeation Chromatography (GPC). |
| Slurry Packing |
Technique for packing a chromatographic column in which the particles of packing material are suspended in a solvent and forced into the column as a slurry. |
| Solvent |
a) The mobile phase. b) The liquid which is used to dissolve the sample. Often, they are the same, i.e., mobile phase is used to prepare the sample solution. |
| Solvent Group |
A classification of solvents according to their effect upon chromatographic selectivity. |
| Sonic Spray Ionization (SSI) |
Method for spraying and ionizing sample solution exiting the end of a capillary tube using only sonic waves. The ionization occurs under atmospheric pressure without heating or high electric fields. |
| Spark Ionization |
Sample ionization done by sparks from capacitor discharges. |
| Spark Source |
Ion source using sparks. |
| Spark Source Mass Spectrometry |
Analyses done using a spectrometer with a spark source. |
| Spike |
Material added to sample in isotope dilution analysis and having a different isotope ratio than the target material in the sample. |
| Spontaneous Desorption Mass Spectrometry (SDMS) |
Mass spectrometry method using the phenomenon of spontaneous desorption of ions from a sample surface installed in an ionization chamber. With this method, there is no special energy or particle bombardment source placed inside or outside the ion source. Field desorption and, as a secondary process, sputtering are said to contribute to the SD ionization mechanism. |
| Spray Ionization |
General name for methods of generating vaporized ions by spraying liquids or sample solutions from the end of a capillary tube using heating, high speed gas flow, high electric fields, or other processes. (e.g. ESI, ISP, TSP, APS) |
| Stable Ion |
Ions generated in the ionization chamber that do not dissociate before reaching the collector. Normally designates ions with life spans of 10-5 seconds or longer. |
| Standard Deviation |
A measure of the uncertainty in a set of random variables; the square root of the average squared deviation from the mean. (see the Formula) |
| Standard Error of Mean |
An estimate of the standard deviation of sample means. |
| Static Secondary Ion Mass Spectrometry (SSIMS) |
SIMS method featuring primary ion current densities (corresponding to SIMS gun flux) of 2 ~ 3 nA/cm2 or less and primarily used in analysis of sample surface components. The method is therefore distinguished from dynamic SIMS, which is used for analysis of components in the depth direction. When the sample is an organic molecule in solid form, the term is changed to organic SIMS or molecular SIMS. |
| Stationary Phase |
The non-mobile chromatographic phase (column packing) with which sample components interact as they are carried through the column by the mobile phase. |
| Step Gradient |
Variation of mobile phase composition in a stepwise manner during a chromatographic run. (see also Gradient Elution and Isocratic Elution). |
| Stepwise Elution |
Variation of mobile phase composition in a stepwise manner during a chromatographic run. (see also Gradient Elution and Isocratic Elution). |
| Surface Ionization (SI) |
Ionization caused by interactions between atoms or molecules and a solid surface. The work function of the surface material, surface temperature, sample ionization energy and other factors contribute to this phenomenon. In a more narrow definition, the term refers to ionization on heated metallic filament surfaces (thermal surfaces). |
| Surface-Induced Dissociation (SID) |
One CID method where dissociation is caused by collisions of the accelerated ions with the surface of a plate, coated with silicon or metal, and not through impacts with a target gas. The dissociation level is strongly dependent on collision energy. |
| Tailing |
Peak distortion where the chromatographic band broadens after the apex. |
| Tandem Mass Spectrometer |
Instrument combining 2 MS instruments, MS1 and MS2, with either the same or different measurement principles. Also called MS/MS spectrometers. |
| Tandem Mass Spectrometry (MS/MS) |
With this method, a single precursor ion is selected from among the ions generated in the ionization chamber of the first MS instrument. Fragment ions generated by dissociation of the precursor ion are then detected at the second MS instrument. In order to promote dissociation, a collision cell or collision tube is installed between MS1 and MS2. CID or SID can be done by then placing a target gas or target plate at this location. |
| Target Gas |
In CID experiments, this term designates the gas with which ions collide in the collision tube. In addition to noble gases (He, Ne, Ar, Kr, Xe), O2 and N2 may also be used. |
| Theoretical Plate |
The plate number, N, is a measure of column efficiency, and is the equivalent of a solute's complete equilibration between mobile and stationary phase. N = 16(x/w)2 where - x is the retention time of a compound and w is the peak width. A high value for N indicates an efficient column |
| Thermal Ionization (TI) |
Ionization caused by contact between atoms or molecules and a heated metallic surface or high temperature gas. |
| Thermal Surface Ionization (TSI) |
A surface ionization method where ions are generated through contact interactions between atoms or molecules and a metal (W or Re) or other surface heated to ~1,000ºC . |
| Thermospray (TS or TSP) |
Spray ionization method where ion-molecule reactions occur between the sample and reagent gas ions. The reagent gas ions are electrolytic ions generated when the sample solution is sprayed by heating from the end of a capillary tube and under a low vacuum of several Torr. This is used as an LCMS interface and can be combined with corona discharge or electron beams. |
| Thermospray Ionization (TSI or TSPI) |
Ionization method using thermospray. Ionization is promoted by corona discharge or other methods after spraying. |
| Time-Of-Flight Mass Spectrometer (TOFMS) |
Mass spectrometry method where ions generated in a pulse state are injected into a region with no electric field then separated according to m/z using differences in flight velocities. |
| Torr |
A unit of pressure. 1Torr = 1mmHg = 133Pa, 1Pa = 10µbar |
| Total Emission Current |
Total electron current emitted from fragments in electron ionization. |
| Total Ion Chromatogram (TIC) |
Chromatogram detected and recorded using the total ion detection method. This is one type of gas chromatogram used in GCMS and other analyses. |
| Total Ion Detection |
Continuous detection of all ions generated by the ion source or all ions within a certain mass number region. |
| Total Ion Monitoring |
Same meaning as total ion detection. |
| Transition State (TS) |
In the reaction coordinates of fragmentation, this term refers to the change state while bonds are breaking and corresponds to the maximum potential energy position. |
| Triple Filament Method |
A surface ionization method wherein 3 filaments are used. Two filaments are used to heat and vaporize the sample and 1 filament, at a very high temperature, is used to ionize the sample. |
| Triple Quadrupole Mass Spectrometer |
An MS/MS device created by connecting 3 quadrupole mass spectrometers in sequence. The first instrument is used for precursor ion selection, the second as a collision tube for CID or SID, and the third for detection of fragment ions created by dissociation of precursor ions. CID spectra of low-energy collisions can be obtained with this instrument. |
| Unified Atomic Mass |
Same meaning as atomic mass unit. |
| Unified Mass Unit |
Same meaning as mass unit. |
| Unstable Ion |
Ion generated in the ionization chamber that dissociates before leaving the chamber. Normally designates ions with short life spans of 10-6 seconds. Since the dissociation of these ions occurs within the ionization chamber, the process is sometimes called in-source fragmentation. |
| UV Detector |
The most popular detector for HPLC, a UV spectrophotometer detects analytes that readily absorb light at the selected wavelength. |
| Vacuum |
Condition where vapor pressure is lower than atmospheric pressure. The pressures are categorized as shown below. Low vacuum - 105 ~ 3.3 x 103 Pa (750~ 25 Torr) Medium vacuum - 3.3 x 103 ~ 10-1 Pa (25 ~ 7.5 x 10-4 Torr) High vacuum - 10-1 ~ 10-4 Pa (7.5 x 10-4 ~ 7.5 x 10-7 Torr) Very high vacuum - 10-4 ~ 10-7 Pa |
| Void |
An empty space within the packed chromatographic column that causes loss of chromatographic efficiency. |
| Void Volume (V0) |
The volume of a chromatographic system between the injector and the detector; V0 is normally assumed to be equivalent to the internal volume of the column alone minus the volume of the column packing material, i.e., the 'empty' space within the column. |
| Wall Effect |
Band spreading which occurs as a result of the mobile phase linear velocity near the walls of the column being different from its linear velocity at the center of the column. It is also caused by frictional forces between the sample molecules and the walls of the column. |
