Derivatisation methods

Derivatisation methods have been applied to the determination of low concentrations of carbonyl groups in polyvinyl chloride and vinyl chloride-vinyl acetate copolymers [55]. Carbonyl groups in the polymer are reacted with 2,4-dinitrophenylhydrazine to produce the corresponding phenylhydrazone. Excess reagent is washed away from the polymer, which is then digested with concentrated sulfuric acid to convert the bound hydrazone to ammonium sulfate, which is then estimated using Nessler s reagent. 

By far the most commonly used reagent for detecting and measuring alkylating agents is 4-(4 -nitrobenzyl)pyridine (NBP) [49-53]. This reacts in the following way  

There are some issues with using this reagent. Some authors have commented on problems with this method, principally due to the instability of the product [55]. 

A number of other spectrophotometric reagents and combinations thereof have been used and compared with NBP 4-p3ridinecarboxaldehyde 4-nitrophenylhydra-zone 4-pyridinecarboxaldehyde 2-benzothiazolylhydrazone 4-acetylpyridine 4-nitrophenylhydrazone 4-acetylpyridine 2-benzothiazolylhydrazone [62]. S -Dodecylisothiouronium bromide has been used with primary and secondary alkyl halides [63]. 4-Nitrothiophenol has been claimed to be better than NBP, but only when used in combination with HPLC and not as a stand-alone reagent [64]. 

10 Adapting analytical methods from fields beyond pharmaceuticals imparities analysis 

The breadth of science that is undoubtedly taking place but has not yet been published does not aid a review of the field. Instead, one must look more widely. The analytical problems faced in doing such trace analysis are not unique to pharmaceutical analysis. The same analytes are often found in other areas, such 

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The most frequently used methods for elemental analysis in plastics (certainly in the past) deal with digestions of some kind. Also, some derivatisation methods (e.g. hydride generation for element analysis, or the equivalent TMAH treatment for molecular analysis) may be used to generate volatile species which are more easily separated from each other by chromatography. Derivatisation reactions are often far from being well controlled. 

Other less volatile monomers such as those found in acrylic materials are detected and quantified in solution by GC. Derivatisation methods are employed for a wide variety of amine and hydroxyl monomers. CEN (Comite Europeen de Normalisation) has published standard methods for the determination of extractable monomers from food-contact materials. These methods are detailed in Table 10. 

Table 9.2 Derivatisation methods for the GC analysis of protein hydrolysates from paint samples...

Table 9.2 summarises the derivatisation methods most used for the analysis of amino acids in paint hydrolysate. In particular ... 

Figure 2.1.1 shows the most common derivatisation methods for anionic surfactants reported in the literature [1]. The first method of LAS determination by GC consisted of a microdesulfonation procedure in which LASs were desulfonated in boiling phosphoric acid at high temperature [2-4] and the corresponding alkylbenzenes analysed. The microdesulfonation method was further improved by introducing additional concentration and clean-up steps [5—11], which allowed the determination of LAS in influent, effluent and river water samples at low qg L-1 levels [7,8] and sediment and sludge samples [8] at pg g-1. In addition to the desulfonation procedure, several derivatisation techniques have been used to make LAS analysis amenable to GC. 

However, most molecules and ions show no fluorescence and so it is necessary to resort to other methods in these cases. Derivatisation methods can be used where the substance of interest is not fluorescent but may be converted into a fluorescent derivative by reaction with a suitable (nonfluorescent) reagent. 

Sometimes it is not necessary to use the selectivity of a chromatographic technique. Sensitive analysis can sometimes be achieved with selective detection in flow injection analysis (FIA). Whilst some of the detectors described below may be appropriate in themselves in favourable cases, in most cases more sophisticated detection regimes are necessary, such as post-injection derivatisation of the analyte. Strategies involving some of the derivatisation methods outlined in Section 4.9.2 may be considered. 

Derivatisation method modihed to produce a stable product... 

Cohean S. (1984) A pre-column derivatisation method for amino acid analysis. Waters Lab highlights No. 220. Available as a downloadable file from the Waters website (http //www. waters.com). 

The N-phenylthiocarbamoylation (PTC) protocol is the basis of a commercial system (the Waters Pico-Tag system) that embodies a thoroughly worked-out procedure using semi-automatic equipment with the aim of ensuring that every mixture analysed is treated in an identical fashion. However, many more examples of systems, custom-built around a favoured HPLC or GLC, are featured in the current literature, particularly using the OPA/fluorescence (Section 4.5.1) and. V-I moc derivatisation methods, rather than the PTC-derivatisation method. 

Analytical characterization of the aroma of Tinta Negra Mole red wine Identification of the main odorants compounds. Analytica Chimica Acta 563,154-164 Pizarro, C. Perez-del-Notario, N. Gonzalez-Saiz, J.M. (2007). Optimisation of a headspace solid-phase microextraction with on-fiber derivatisation method for the direct determination of haloanisoles and halophenols in wine. Journal of Chromatography A 1143,26-35... 

Piccirillo, A., Scalarone, D., Chiantore, O. Comparison between off-hne and on-line derivatisation methods in the characterisation of siccative oils in paint media. Journal of Analytical and Applied Pyrolysis, 74, 2005, 33-38. 

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