Fluorescence detectors response characteristics

Methods. Absorption spectra were recorded using an Hitachi model 150-20 spectrophotometer/data processor system. Uncorrected steady-state fluorescence emission spectra were recorded using a Perkin-Elmer MPF-44A spectrofluorimeter. These spectra were collected and stored using a dedicated microcomputer and then transferred to a VAX 11/780 computer for analysis. Fluorescence spectra were corrected subsequently for the response characteristics of the detector (21). Values of the fluorescence quantum yield, <) , were determined relative to either quinine bisulfate in IN H2S04 )>f =... 

The detector converts a change in the column effluent into an electrical signal that is recorded by the data system. Detectors are classified as selective or universal depending on the property measured. Selective (solute property) detectors, such as fluorescence detectors, measure a physical or chemical property that is characteristic of the solute(s) in the mixture only those components which possess that characteristic will be detected. Universal (bulk property) detectors measure a physical property of the eluent. Thus, with refractive index (RI) detectors, for example, all the solutes which possess a refractive index different from that of the eluent will be detected. Selective detectors tend to be more sensitive than universal detectors, and they are much more widely used. Universal detectors are more commonly used in preparative chromatography, where a universal response is desired and sample size is large. 

Well over 90% of all samples examined by FT-Raman spectroscopy with 1064-nm excitation yield an identifiable spectrum. For those samples that still fluoresce, longer-wavelength lines are available. For example, Asselin and Chase [4] have demonstrated that the spectrum of copper phthalocyanine can be measured with the 1339-nm line of Nd YAG (see Figure 18.4), while the spectram of this compound is swamped by fluorescence when the 1064-nm line of this laser is used, as shown in Figure 18.5. Because of the longer wavelength of this laser and the response characteristics of the germanium detector, however, the spectmm could only be measured to a Raman shift of 1800 cm. ... 

The ideal HPLC detector should have the same characteristics as those required for GC detectors, i.e. rapid and reproducible response to solutes, a wide range of linear response, high sensitivity and stability of operation. No truly universal HPLC detector has yet been developed but the two most widely applicable types are those based on the absorption of UV or visible radiation by the solute species and those which monitor refractive index differences between solutes dissolved in the mobile phase and the pure mobile phase. Other detectors which are more selective in their response rely on such solute properties as fluorescence, electrical conductivity, diffusion currents (amperometric) and radioactivity. The characteristics of the various types of detector are summarized in Table 4.14. 

Fig. 1.4. (a) Characteristic (H and D) curve of a mam-mographic screen-film system. Optical density (OD) of the processed film is plotted versus the log of the relative X-ray exposure to the fluorescent intensifying screen, (b) Characteristic response of a detector designed for digital mammography (from Pisano et al. 2004. With permission)... 

Detectors are based on a selective response for the solute, such as UV-absorbance or fluorescence, or on a bulk property of the mobile phase which is modified by the solute, such as refractive index. Ideally, detectors shoiild have the following characteristics ... 

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