Biological-Physiological Methods of Detection

Even quantitative determinations can be performed using biological-physiological methods. These are discussed by Jork and Weins [114] using the example of enzymatic in situ detection of pollutants. 

Toxicity screening of complex mixtures following separation on a HPTLC plate is a new technique invented by Bayer. Now ChromaDex (see Section 12.5 for the address) has incorporated this technology into a commercial kit (Bioluminex ) utilizing the bioluminescent bacteria. Vibrio fischeri. CAMAG has marketed the BioLumini-zer for the detection and documentation (see Section 8.8). 

The pubhshed work on this subject encourages us to look forward to even more pubhcations on these highly specific and sensitive methods. 

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Just like the physical and microchemical methods of detection, the indirect, biological-physiological detection procedures are very selective when apphed to thin-layer chromatography. Here it is not chemical functional groups or particular physical properties that are selectively detected but effects on highly sensitive biodetectors . The following detection techniques have been employed ... 

Three methods of detection (UV absorbance, fluorescence, and electrochemical activity) are applicable for the analysis of water-soluble vitamins. Currently, UV absorption detection is used in many LC applications for water-soluble vitamins. A simultaneous assay of several vitamins with several wavelengths along with information of peak purity can be accomplished with a diode array absorbance detector. The detection limit of a UV detector is in the order of 1-10 ng (10-100 pmol), which is poorer than that of fluorescence and electrochemical detectors but often sufficient for analysis for many vitamins in foods and physiological samples (Table 4). The lack of selectivity of UV detection may cause problems with interfering and co-eluting contaminants especially in biological samples, thus necessitating sample purification prior to LC. 

These methods of detection do not exploit chemical or physical properties but the biological-physiological activity of substances. They are mostly employed for the detection and determination of antibiotics, alkaloids, insecticides, fungicides, mycotoxins, cytotoxines, vitamins, hot or bitter substances, and saponines. 

Biological-physiological detection The methods involved here take account of the biological activity of the separated components independent of their physical or chemical properties [12]. 

Physical detection methods are based on inclusion of substance-specific properties. The most commonly employed are the absorption or emission of electromagnetic radiation, which is detected by suitable detectors (the eye, photomultiplier). The / -radiation of radioactively labelled substances can also be detected directly. These nondestructive detection methods allow subsequent micropreparative manipulation of the substances concerned. They can also be followed by microchemical and/or biological-physiological detection methods. 

Fig. 54 Fields of application and frequency distribution of biological-physiological detection methods.

Three types of detection methods for TLC may be distinguished, namely physical, microchemical and biological-physiological. The more common detection methods for polymer additives in TLC are given in Figure 4.8. Detection is an off-line process, thus several detection techniques may be used one after the other. 

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