Spectrochemical Measurements with Multichannel Integrating Detectors

Abstract

This is the second article in a two-part series describing the operation, performance characteristics, and spectroscopic application of charge transfer devices (CTDs) in analytical chemistry. The first article in the series describes the new generation of integrating multichannel detectors, the charge injection device (CID), and the charge-coupled device (CCD). The first article also discusses the spectroscopically pertinent characteristics of these detectors and presents performance data for representative devices. This article covers three major topics related to the optimum use of integrating detectors in analytical spectroscopy. The advantages of employing integrating multichannel detectors in analytical spectroscopy, rather than a single detector in a wavelength scanning system or an interferometer, are discussed. Included are detector read noise considerations which have not been considered in previous performance comparisons. When one is employing an integrating detector in luminescence, absorption, and emission applications, achievable sensitivity is dependent on differing detector parameters. In the first case, quantum efficiency and read noise are of the greatest importance, whereas in the later two cases, dynamic range is most significant. The calculation of minimum detectable analyte signal for these three techniques illustrates the differences between integrating detectors and detectors which produce a photocurrent. This discussion also illustrates the great sensitivity that can be achieved with a modern CTD detector. Factors pertaining to the optical design of spectrometers which efficiently use CTDs are presented, along with examples of linear and two-dimensional dispersive polychromators employing CTDs. Low-light-level imaging and a nonconventional method of using a CCD for rapid scanning spectrophotometry are also discussed.