Photodiode array detectors operating principles

The photodiode-array based UV absorbance detector, usually abbreviated as either the PDA or DAD, but in this chapter as DAD, has been used in a wide range of applications since it was introduced commercially almost two decades ago. It allows collection of the complete UV absorbance spectrum of the HPLC column eluent The general principles and operation of the DAD have been reviewed by Huber and George in a book on DADs and their application [2]. This book is also a good primer on the use of the DAD in fields such as clinical, pharmaceutical, environmental, polymer, and biotechnology analyses. 

Milano et al. [153, 154] and Cook [34] introduced an approach to derivative spectra by substituting electronic wavelength modulation for the mechanical systems used in derivative spectrometers. This effect is achieved by superimposing a low-amplitude, periodic wave form on the horizontal sweep signal. In this way spectra were generated. Warner et al. [155] applied a vidicon detector for fast detection of fluorescence spectra and obtained derivatives of the stored data by digital computation. Cook et al. [156] also made use of a silicon vidicon detector for multichannel operations in rapid UV-VIS spectrophotometers with the possibility of first-order differentiation. For the same purpose Milano et al. [93, 157] used a multichannel linear photodiode array for detection of spectra in polychromator optics and stored data manipulations (d ). Technical explanations of the principles of diode array and vidicon devices cem be found in [158-161]. 

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