Detection systems diode array type

The development of online sample procedures is critically important, for with them sensitivity increases, losses are prevented, and automation is made easy, as is demonstrated by the development of the system for automated measurement of organic micropollutants in surface water (SAMOS) LC and SAMOS GC (45,46,53,54). The SAMOS LC is based on SPE sample preparation, column LC, and diode array detection (53). Moreover, all types of MS detectors for HPLC can be coupled to the SAMOS. 

Schematically, two main systems can be used to collect 3D fluorescence data (time, wavelength, number of photons, see fig. 1). In a first type of system, light is directed into a monochromator connected to a photomultiplier tube and then to a fast oscilloscope (PM detection). The experimentalist thus collects luminescence decays at various wavelengths. This system is known to be very efficient for luminescence decay acquisition but is very time-consuming for the acquisition of emission spectra. In the second type of system, light is directed to a diode array detector (or CCD camera) and a subsequent electronic detection device (diode detection). The experimentalist collects emission spectra at various delay times (time zero for the pulse entering in the sample). This system is very efficient for emission data acquisition but, on the other hand, time-consuming for luminescence decay acquisitions. From this very schematic description, it appears that a system combining the two types of detections would be the optimum.

The most commonly-used detectors are those based on spectrophotometry in the region 184-400nm, visible ultraviolet spectroscopy in the region 185-900nm, post-column derivativisation with fluorescence detection (see below), conductivity and those based on the relatively new technique of multiple wavelength ultraviolet detectors using a diode array system detector (described below). Other types of detectors available are those based on electrochemical principles, refractive index, differential viscosity and mass detection. 

In the past, molecular luminescence spectrometry was always conducted with single channel systems involving a photomultiplier tube (PMT) as the detector. The availability of multichannel detectors with internal gain has provided a new powerful tool for luminescence measurements, and several types of applications have been reported (1-15). This paper is concerned with the application of an intensified diode array dynamic molecular fluorescence and chemiluminescence measurements. In this paper the types of measurements and analytical systems for which multichannel detectors are used in our laboratory are introduced. Next the specific IDA system used is presented along with important hardware and software considerations. Third, the characteristics of the IDA detector are reviewed to give some perspective about its influence on the quality of measurements. Finally, some typical applications to chemical systems are presented to illustrate the advantages of multichannel detection. 

The detector type will vary depending on the application however, the most commonly used systems are diode array UV/Vis. Other detectors are available, such as electrochemical and mass spectrometry detectors. Detectors used will vary depending on the type of chromatography and the type of analyte required to be detected (e.g., when carrying out ion exchange chromatography, an electrochemical detector is required because a UV/Vis detector will not detect the ions). This will be discussed further in Chapter 5. 

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