Detection, at two different wavelengths

Figure 6.7 LC chromatograms with photodiode array detection at two different wavelengths of the leachate sample (for peak assignment, see Table 6.3). Reprinted from Benfenati, E., Pierucci, P., Fanelli, R., Preiss, A., Godejohann, M., Astratov, M., Levsen, K., and Barcelo, D.,. /. Chromatogr., A, 831, 243-256, copyright (1999), with permission of Elsevier Science...

As noted in the preceding table, elution of PAHs is detected by UV absorbance at two different wavelengths 280 nm and 365 nm. Fluorescence detectors are also applicable to the HPLC analysis of PAHs (9, 19). The UV detector monitors the sample simultaneously at two wavelengths, aiding in compound identification. For a specific compound, the ratio of absorbances at two different wavelengths is an intrinsic physical characteristic. Therefore, it is possible, in principle, to identify a sample analyte by this characteristic ratio. The chromatographic retention time of each of the specific peaks observed in the sample eluate is compared with those of known standard compounds for tentative analyte identification. For quantitation, peak areas of each standard, at each of six... 

Secondary amino acids, imino acids , such as proline and hydroxyproline, do not possess an a-amino group, and react with ninhydrin to form a yellow product which is usually detected at 440 nm. Therefore, amino acid analyzers are equipped with a photometer capable of measuring at two different wavelengths (570 nm and 440 nm). The sensitivity of this detection method is about 200 pmol. 

Figure 29-8 illustrates the separation of polycyclic aromatic hydrocarbons extracted from a carbon black. Detection was by fluorescence excited at two different wavelengths. Note the selectivity provided by this technique. The chromatogram was obtained by using a 40 m X 50 pm inside-diameter capillary coated with a 0.25-pm film of 50% phenylpolysiloxane. The mobile phase was pentane at 210°C, and the following program was used initial mobile-phase density held at... 

Ratio Pyrometers The ratio pyrometer is also called the two-color pyrometer. Two different wavelengths are utilized for detecting the radiated signal. If one uses Wien s law for small values of XT, the detected signals from spectral radiant energy flux emitted at the wavelengths and 2 with emissivities and are... 

Figure 6.7 shows the chromatograms of an extract of a leachate sample at two different detection wavelengths which reveal that the separation efficiency... 

Figure 6.9. LC chromatograms and ratiograms using UV detection at two wavelengths (255 and 280 nm) with four different mobile phases. Reprinted with permission from A. C. J. H. Drouen, H. A. H. Billiet, and L. De Galan, Anal. Chem. 1984, 56, 971. Copyright 1984, American Chemical Society.

Figure 3.18 Chromatograms of a sample containing two compounds A and B, for which the UV spectra are different. According to the choice of detection wavelength, the chromatogram will not have the same aspect. On the right the chromatograms represent a mixture of several pesticides recorded at three different wavelengths which illustrates this phenomenon. In quantitative analysis therefore the response factors of each of the compounds must be determined prior to the analysis (cf Quantitative analysis, Chapter 4).

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