Methylcarbamates derivatization

Naphthyl)ethyl isocyanate, chiral derivatizing reagent, 6 76t 1-Naphthyl-Al-methylcarbamate, 17 84 Napierian absorbance, 23 126 Naples yellow, 14 792 Napping, of staple-fiber non woven fabrics, 17 515... 

The methylcarbamate insecticides are particularly suitable to derivatization owing to the availability of the replaceable proton on the methylcarbamyl nitrogen atom. The proton may be replaced by a wide variety of groups to give reasonably stable products, as indicated by the general scheme below... 

Attempts to react methamidophos with the corresponding chlorosulfinylcarbamate intermediate, however, resulted in products which were unstable and of no value as proinsecticides. In general, phosphoramidothioates such as methamidophos are more difficult to derivatize than the methylcarbamate esters and therefore are less useful as precursors to proinsecticides. 

The CUSAL-HPLC couple has been combined additionally with pre- or post-column derivatization. Thus, pre-column derivatization was used for the determination of colistin A and B in feeds following USAL, the analytes were derivatized with o-phthaldialdehyde/2-mercaptoethanol and separated by HPLC for fluorimetric detection [48]. The experimental set-up used is depicted in Fig. 4.1 OA. Another application of CUSAL-HPLC is the determination of A/-methylcarbamates in soils and food [49] (see Fig. 4.10B), where the analytes were also derivatized with o-phthaldialdehyde after separation for fluorescence-based monitoring. A number of steps of the process including leaching, filtration, solid-phase extraction, liquid chromatographic separation, post-column derivatization and fluorescence detection were performed on-line, all in an automated manner. 

PHWE-LC systems have been utilized, for example, to determine N-methylcarbamates in food. PHWE was done at 75 °C and a combination of static and dynamic extraction was used. In this system, the effluent from the chromatograph was coupled with a flow injection manifold where the N-methylcarbamates were hydrolyzed and then derivatizatized by reaction with a fluorogenic reagent (o-phthalaldehyde). The derivatized analytes were driven to a fluorimeter equipped with a flow-cell allowing monitoring (31). 

The reasons for derivatizing carbamates, apart from their thermolability during the gas chromatographic analysis, include increased detector sensitivity (particularly with electron capture detection), increased volatility, better chromatography separation, apphcability to multiresidue and confirmatory analysis, and enhanced compound stability. There are two general approaches to the analysis of Af-methylcarbamates by derivatization, namely derivatization of the intact pesticides and derivatization of a hydrolysis product (one of which will always be the volatile methylamine). The reactions typically used to obtain derivatives of both intact and hydrolysis products of A-methylcarbamates are methylation, silylation, halogenation, acylation, and esterification. 

A continuous SPE system coupled to a gas chromatograph was used for the preconcentration and determination of A-methylcarbamates in water samples. The continuous system (Figure 24.4) comprised a peristaltic pump furnished with pumping tubes, an injection valve, and a laboratory-made adsorption column placed in the loop of the injection valve. Also, a LLE derivatization module coupled online to a gas chromatograph was used for the determination of carbamate pesticides in aqueous samples. The manifold consisted of a peristaltic pump, pumping... 

Ballesteros, E., Gallego, M., and Valcarcel, M., Automatic determination of A-methylcarbamate pesticides by using a liquid-liquid extractor derivatization module coupled online to a gas chromatograph equipped with a flame ionization detector, J. Chromatogr., 633, 169-176, 1993. 

The pesticide benzo[/7]thienyl methylcarbamate has been derivatized with methanesulphonyl chloride for g.l.c. analysis. Octapeptides into which benzo[ ]thienylalanine has been introduced as a tryptophan congener have been synthesized. ... 

Y.S. Wu, H.K. Lee and S.F.Y. Li, A fluorescence detection scheme for capillary electrophoresis of V-methylcarbamates with on-column thermal decomposition and derivatization. Anal. Chem., 72, 1441-1447, 2000. 

On-capillary derivatization Quaternary ammonium surfactants (CTAB) catalyzing the thermal decomposition of W-methyl carbamates to liberate methylamine Separation buffer contains the derivatizing components o-phthaldialdehyde/ 2-mercaptoethanol W-methylcarbamates o-Phthaldialdehyde is the most popular fluorescence reactant An Intact capillary can serve consecutively as chamber for separation, decomposition, derivatization, and detection... 

Loading test experiment was performed on a methylcarbamate CF6 CSP with truns-l-amino-2-indanol in the polar organic mode. As shown in Fig. 15, 3.37 mg of the primary amine can be baseline separated in 20 min on an analytical column (250x4.6 mm). Furthermore, cyclofructan-type CSPs operates best in organic solvents and supercritical fluid solvents as well, which makes the sample recovery much easier than with aqueous mobile phases. These characteristics make the cyclofructan-type CSPs viable candidates for the preparative separations of primary amines. In addition, high loading of N-blocked amino acids were also reported on aromatic-derivatized CF6 CSPs [39]. 

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