What is a high performance (HP) spectrophotometer?

High performance spectrophotometers are the premier instruments in both the UV/Vis and UV/Vis/NIR wavelength range. The difference between these two optical designs is the addition of a second diffraction grating and a second detector (PbS or InGaAs) for the NIR spectral range. This, however, is not what makes them high performance. There is a key component of HP instruments that makes them able to measure very low values of %T (or high absorbance). By adding a second diffraction grating (top right) for each wavelength region (UV/Vis and NIR), the stray light of the instrument is reduced by a considerable amount.

This is a total of four gratings in the instrument, two each of the UV/Vis and NIR diffraction grating. All high-performance instruments have two of the same type gratings working in tandem to reduce instrumental stray light. The reduce stray light for dual monochromator spectrophotometers is what defines them as high performance (see optical diagram above). HP spectrophotometers are able to measure between 6 to 10 absorbance units in the UV/Vis and up to 7 to 8 absorbance units in the NIR with an InGaAs detector.