Carbamates sample preparation

The applicability of cinchonan carbamate CSPs for bioanalytical investigations using HPLC-ESI-MS/MS has been demonstrated by Fakt et al. [120]. The goal was the stereoselective bioanalysis of (R)-3-amino-2-fluoropropylphosphinic acid, a y-aminobutyric acid (GABA) receptor agonist, in blood plasma in order to determine whether this active enantiomer is in vivo converted to the 5-enantiomer. In this enantioselective HPLC-MS/MS bioassay, sample preparation consisted of... 

In an assay that offers acceptable HOPi/ri ratios for the carbamates, potential HOP can be estimated by preparing the sample under conditions that insure hydrolysis of the sulfamates. Unfortunately, the conditions specified for sample preparation in the standard mouse bioassay are not sufficiently acidic to insure complete hydrolysis ( ). As currently employed in state monitoring laboratories, the mouse assay may substantially underestimate the potential HOP of samples containing the sulfamate toxins. 

This chapter deals with the properties of carbamate pesticides, many of which influence the design and choice of analytical methods for their determination. It reviews the chromatographic techniques used to quantify carbamate pesticides in environmental samples, with special emphasis on GC and LC. Other chromatographic techniques, viz., capillary electrophoresis (CE), thin-layer chromatography (TLC), supercritical fluid chromatography (SFC), and sample preparation procedures, are also discussed. 

Automatic sample preparation methods for the determination of oarbon-14 and/or tritium, and carbon-14 and/or sulfur-36 in dual labelled samples by liquid scintillation counting are presented. The sample is burnt in a stream of oxygen, and the combustion products carrying radioisotopes are subsequently separated and collected for radioactivity determination. Tritium is measured as water, carbon-14 as "carbamate" and sulfur-35 as sulfuric acid. The procedures run automatically, they are free of memory effect and cross contamination, and provide quantitative recovery. 

Methyl 5-hydroxy-2-benzimidazole carbamate (MHBC, Figure 7.4), a urinary metabolite of the pesticides carbendazium, benomyl and thiophanate-methyl, has been measured using an ODS-modihed silica analytical column with methanol-aq. ammonium acetate (approximately 60 mmol L , pH 8) (27 + 73) as eluent and ED (PGE, +0.22 V vs Pd). Sample preparation was by a complex procedure involving SPE (SCX-modified silica) of hydrolysed specimens. No internal standard... 

Lawrence [475] and Ryan and Lawrence [476] chromatographed insecticidal carbamates and other agricultural chemicals in the form of perfluorinated acyl derivatives. Of these they recommended HFB derivatives as most suitable. They prepared them by treatment with HFB anhydride in benzene in the presence of trimethylamine, as follows. A 15-jul volume of HFB anhydride and 0.4 ml of 0.1 M trimethylamine in benzene were added to 1—10 /rg of insecticide (dried extract of a food sample) in a 20-ml test-tube. 

A stirred solution of the nitroaniline (20 mmol) and ethyl chloroformate (60 mmol) in xylene (30 ml) is heated under reflux (14-18h). The solvent is removed in vacuo to give the pure carbamates as oils in quantitative yields. They can be used without further purification, but analytical samples can be obtained by preparative thin layer chromatography using petroleum ether-ethyl acetate as the eluent. The products have Vniax 1710 cm. ... 

For colorimetric analysis, plasma and urine samples are prepared by alkalinization and chloroform extraction. Methocarbamol couples with diazotized dinitroaniline to give an orange-red compound33. Alternatively, colorimetric determination with chromotropic acid is possible after alkaline hydrolysis (10 mins, in boiling water) of the carbamate and periodate oxidation to formaldehyde34. 

Some applications of FTIR are shown in Figure 7.7. The classic example of using in-line FTIR is the Merck investigation of [5-lactam formation [13]. The reaction was shown to proceed through the ketene intermediate 21. FTIR was also used to determine optimal conditions for the low-temperature alkynylation of the ketone 22 [14] and for the methylation of indole 23 [15]. The conversion of phenol 24 to carbamate 25 and isothiocyanate 26 was conveniendy monitored by FTIR [16] due to the hot temperature and reactive nature of the reaction components, special handling would have been required to withdraw reaction aliquots and prepare samples. 

ZSM-22 (TON) can be produced from potassium based 1,6 hexamethylenediamine synthesis mixture, while, ZSM-34 (an OFF/ERI intergrowth) is synthesized from the same synthesis mixture with the addition of sodium. NMR analyses of the as-synthesized zeolite samples indicated the presence of a carbonyl species in all of the ZSM-34 samples, but not in any of the preparations that produced ZSM-22. The carbonyl species was present only after the synthesis mixture was heated above ambient temperature. Molecular modeling studies calculated a favorable fit of the carbamic species within the pore system of the Erionite suggesting a reason for the formation of the OFF/ERI intergrowth. 

The analysis of pesticide residues and metabolites in foods can be a difficult problem because of the complexity of the matrix and the trace levels at which the analytes must be detected. Capillary SFC has been shown to be a very effective technique for the analysis of trace levels of pesticides, especially when a selective detector such as the NPD is used (18). Figure 7 shows an example of the determination of selective carbamate pesticides in parsley. The sample was prepared by extraction of 1 gram of... 

Anticipating a B-alkyl Suzuki-Miyaura cross-coupling reaction between the Cl-Cl 4 and C15-C24 subunits, alcohol 57 was smoothly converted to vinyl iodide 60 in seven steps, including a Pt02 reduction of the crowded triple bond of intermediate 59, without overreduction. The coupling of the vinyl iodide 60 and C15-C24 subunit was performed by using trialkyl boronate species 61, prepared from alkyl iodide 46, under [Pd(dppf)Cl2] and AsPhs conditions to afford the DDM backbone 62 in 60% yield (Scheme 14). Finally, after carbamate formation and total deprotection, DDM 1 was obtained in 70% yield. The spectroscopic and analytical data of the synthetic samples of as well as their in vitro cytotoxicity levels were in full accord with those of the natural product reported in the literature. 

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