Photodiode array detectors in UV-VIS spectroscopy: part II

Abstract

In Part I, which appeared in last month's issue, the theoretical aspects of diode array UV-VIS spectroscopy were discussed. The second article in this two-part series describes the applications of diode arrays in analytical chemistry.Applications of the linear photodiode array (LPDA) spectrometer in the UV-VIS spectral region can be considered under four headings: (1) molecular spectroscopy, (2) rapidscanning detection for time-dependent phenomena, (3) rapid-scanning detection in HPLC, and (4) other ap-plications, which include low-lightlevel applications and atomic spectroscopy. SpectroelectrochemistryThe combination of electrochemistry and spectroscopy was first reported in 1964 (1). Since that time spectroelectrochemistry has been used to study the redox chemistry of inorganic, organic, and complex biological molecules. The redox reactions in these systems occur on the second to millisecond time scale. Consequently, the ability of the LPDA spectrometer to measure spectra on a millisecond time scale is important. Although Raman, fluorescence, and internaland specular-reflectance spectroscopy have been used in spectroelectroche-

Capillary supercritical fluid chromatography with ultraviolet multichannel detection of some pesticides and herbicides

“…While capillary SFCwas being developed, gains were made in the application of multichannel photodiode array based UV/vis detectors in liquid chromatography [5]. Photodiode array detectors can perform rapid acquisition of complete UV/vis spectra.…”

High performance liquid chromatography

“…Photodiode array technology allows continuous scanning[25] of the absorbance spectrum of the chromatographic eluant, thus eliminating the need to stop the flow of the mobile phase. Photodiode array technology allows continuous scanning[25] of the absorbance spectrum of the chromatographic eluant, thus eliminating the need to stop the flow of the mobile phase.…”

“…With analyte in the sample cell the light beams are refracted to differing extents and different amounts of radiation fall on the photodetector.The disadvantages of this system are (a) two prisms are required to cover the range of RI of solvent encountered (l.31-l.55); (b) small volume cells (5111) help enhance sensitivity; however the limited sensitivity (x 1000 less than ultraviolet) and stability are the principle limits to the universal application of this technique 25. The refractometer shown (Figure 6.25) is based on Fresnel's Law, which states that the fraction of light reflected at a glass-liquid interface varies with the angle of incidence and the RI of the liquid.…”