Methylcarbamates fluorescence

N-methylcarbamate and N,N -dimethylcarbamates have been determined in soil samples by hydrolyses with sodium bicarbonate and the resulting amines reacted with 4-chloro-7-nitrobenzo-2,l,3-Oxadiazole in isobutyl methyl ketone solution to produce fluorescent derivatives [81]. These derivatives were separated by thin layer chromatography on silica gel G or alumina with tetrahydrofuran-chloroform (1 49) as solvent. The fluorescence is then measured in situ (excitation at 436 nm, emission at 528 and 537nm for the derivatives of methylamine and dimethylamine respectively). The... 

KMS Sundaram, J Curry. High-performance liquid chromatographic method for the analysis of aminocarb, mexacarbate and some of their N-methylcarbamate metabolites by postcolumn derivatiza-tion with fluorescence detection. J Chromatogr A 672 117-124, 1994. 

The sulfones of 4-benzo[6]thienyl-ZV-methylcarbamate and its 2,3-dihydro derivative possess insecticidal activity.610 Several mero-cyanine dyes have been prepared from thioindoxyl-1,1-dioxide,735 736 and a number of 2-arylbenzo[6]thiophene-l, 1-dioxides are fluorescent and are useful commercially (e.g., as dyes 737 and in photographic films738). 2-(p-Isocyanatophenyl)benzo[6]thiophene-l, 1-dioxide has been incorporated in copolymers of use in the printing industry-302... 

Most of the older methods of fluorimetric analysis of pesticides involved hydrolysis to form fluorescent anions. Co-ral (coumaphos) [147] was hydrolyzed in alkali to the hydroxybenzopyran, which was subsequently determined by means of its fluorescence. Guthion (azinphosmethyl) was hydrolyzed to anthranilic acid for fluorimetric analysis [148,149]. A method was developed [150] for Maretin (N-hydroxynaphthalimide diethyl phosphate) in fat and meat which involved hydrolysis in 0.5 M methanolic sodium hydroxide followed by determination of the fluorescence of the liberated naphthalimide moiety. Carbaryl (1-naphthyl N-methylcarbamate) and its metabolites have been determined by a number of workers using base hydrolysis and the fluorescence of the resulting naphtholate anion [151-153]. Nanogram quantities of the naphtholate anion could be detected. Zectran (4-dimethylamino-3,5-xylyl N-methylcarbamate) has been determined by the fluorescence of its hydrolysis product [154]. The fluorescence behaviour of other carbamate insecticides in neutral and basic media has been reported [155]. Gibberellin spray used on cherries has been determined fluorimetrically after treatment with strong acid [156]. Benomyl (methyl N-[l-(butylcarbamoyl)-2-benzimidazolyl]carbamate) has been analyzed by fluorimetry after hydrolysis to 2-aminobenzimidazole [157]. 

Methylcarbamate insecticides have been recently labeled with DNS-C1 [145]. The procedure involves the hydrolysis of the carbamates with 0.1 M sodium carbonate to form a phenol and methylamine [166]. The two hydrolysis products are labeled with DNS-C1 and subsequently detected and determined quantitatively by TLC on silica gel layers by scanning spectrofluorimetry in situ. The reaction conditions were examined, and optimum conditions for hydrolysis and labeling were established [167]. The overall reaction scheme is shown in Fig. 4.62. The phenol derivatives of a number of N-methylcarbamates have been separated by one- and two-dimensional TLC [168], and the fluorescence behaviour and stability of the derivatives have been examined [169]. Most of the DNS derivatives fluoresce at similar wavelengths (excitation, ca. 365 nm emission, ca. 520 nm). The fluorescence spectrum of a typical DNS derivative is shown in Fig. 4.63. The method has been applied successfully to the analysis of low concentrations of carbamates in water and in soil samples with little or no clean-up being required [170,171]. Amounts as low as 1 ng of insecticide can be detected instrumentally. Visual limits of detection are ca. 5-10 ng per spot. 

NBD-C1 reacts with the liberated amines of dithio- and thio-carbamates to produce fluorescent derivatives. The products are separated by TLC [177]. The method is similar to that described earlier for methylcarbamate insecticides (see Section 4.2.4.2.2). The carbamates are hydrolyzed in base and the liberated amines are treated as described for methylcarbamates or by the technique described for biogenic amines (Section 4.2.1.2.2). 

Miles and Moye [171] have shown that several classes of nitrogen containing pesticides responded to a high performance liquid chromatography post-column reaction detector that employed ultraviolet photolysis with optional reaction with o-phthalicdicarboxaldehyde-2-mercaptoethanol followed by fluorescence detection. It was applied to the determination of jV-methylcarbamates, carbamoyl oximes, carbamethoic acids, dithiocarbamates and phenyl ureas, phenyl amides and phenyl carbamates in groundwater. See also Table 4.3. 

N-Methylcarbamate insecticides have been labelled with dansyl chloride (28). The procedure involves hydrolysis with aqueous base to form a phenol and methylamine. The reagent reacts rapidly with both compounds and the newly formed fluorescent derivatives can then be applied and separated by tic (29, 30). A typical reaction scheme is shown in Figure 7. Detection limits are good ( 1 ng per spot) and dansylation of pesticides can be accomplished with extracts from water and soil samples (31J. ... 

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. 

A. Caballo-Lopez, M.D. Luque de Castro, Continuous ultrasound-assisted extraction coupled to on line filtration—solid-phase extraction—column liquid chromatography—post column derivatisation—fluorescence detection for the determination of N-methylcarbamates in soil and food, J. Chromatogr. A 998 (2003) 51. 

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... 

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