Determination Of N-methylcarbamates Research Articles

Determination of N-methyl carbamate pesticides in diet samples by high performance liquid chromatography-linear ion trap mass spectrometry with gel permeation chromatography cleanup

A method for the determination of N-methyl carbamate (NMC) pesticides in diet samples was developed by high performance liquid chromatography-linear ion trap mass spectrometry (HPLC-LIT-MS). The samples with the isotope internal standard were ultrasonically extracted with acetonitrile saturated with cyclohexane, and then cleaned-up by passing through gel permeation chromatographic (GPC) column. The LC separation was performed on a CAPCELL PAK CR column (100 mm x 2.1 mm, 5 microm; SCX-C18 (1 : 4)) using acetonitrile and 5 mmol/L ammonium formate/0.1% (v/v) formic acid aqueous solution as mobile phases (gradient elution) at a flow rate of 0.2 mL/min. The ionization of the analytes was performed by positive electrospray mode. Selective reaction monitoring (SRM) was used for the monitoring of MS3 transitions for each compound. The internal standard was used for quantitation. The average recoveries were in the range of 60.4% - 114%, and the relative standard deviations (RSDs) were all not more than 16.2%. The limits of detection (LODs) were 0.001-0.010 mg/kg. The method was successfully applied to the determination of 15 compounds of interest in nine foodstuffs from the fourth Chinese Total Diet Study (TDS) performed in 2007, and aldicarb and carbofuran were found in several samples.

Coupled column liquid chromatography for the rapid determination of N-methylcarbamates and some of their main metabolites in water

A sensitive and selective coupled-column liquid chromatography (LC-LC) method was developed for the trace level determination of some N-methylcarbamates and some of their main metabolites as aldicarb, aldicarb-sulphoxide, aldicarb-sulphone, carbofuran and 3-hydroxicarbofuran in drinking and ground waters. The limit of determination can be reduced to 0.1 μg.L−1 by solid phase extraction with a subsequent evaporation step. Environmental samples spiked at 0.1 μg.L−1 were preconcentrated off-line with graphite carbon and then analyzed by LC-LC with UV detection yielding average recoveries between 81–109% (n=5) with RSD between 5–9%. The overall procedure allowed a sample throughput of up to 30 samples per day.

Separation and determination of pesticides by capillary electrophoresis. II. Determination ofN-methylcarbamates in drinking water by micellar electrokinetic chromatography with SPE and on-column enrichment

This article describes a new method for the determination of ultra trace levels of 12 N-methylcarbamates in drinking water via micellar electrokinetic chromatography (MEKC). Two steps were employed to enhance the detection sensitivity. The sample was first preconcentrated by C18 bonded SPE cartridge and then further enriched through on-column stacking. With this two-step enrichment procedure, the method permits separation and UV detection of N-methylcarbamates at the 0.1-ppb level. This new alternative for the determination of carbamates in drinking water is convenient and fast and consumes practically no organic solvent. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 529–535, 1998

On-Line Preconcentration and Gas Chromatographic Determination of N-Methylcarbamates and Their Degradation Products in Aqueous Samples

A continuous liquid−solid extraction system coupled to a gas chromatograph for the preconcentration and determination of N-methylcarbamates and their corresponding phenols in water is reported. Various sorbent materials were assessed, of which XAD-2 provided the best results in the preconcentration of propoxur, carbofuran, carbaryl, 2-isopropoxyphenol, 3-hydroxycarbofuran, and 1-naphthol. The proposed method is highly sensitive to trace levels of the analytes; it features detection limits between 0.7 and 1 μg/L, which are substantially lower than those afforded by flame ionization detection. Changes in three river water samples containing only carbamate pesticides or phenols and pesticides plus their hydrolysis products (phenols) at the microgram per liter level were studied under natural conditions over a 6-week period; the rate of degradation was lower for the N-methylcarbamates than for their respective phenols. The proposed continuous system was evaluated for environmental samples without detectable residues of pesticides.

On-line sample handling strategies for the trace-level determination of pesticides and their degradation products in environmental waters

An overview of the use of on-line techniques is presented. First, it includes the on-line coupling of solid-phase extraction and liquid chromatography, which is certainly the most commonly used automated technique really well adapted to the multiresidue analysis of pesticides in aqueous samples. The different parameters which govern the method (dimension of the pre-columns, type of sorbents, pre-columns in series, quantitative analysis) are discussed and applications to various waters are presented. Emphasis is given to the limits of detection obtained using UV diode array, fluorescence or electrochemical detection modes. The on-line post-column reaction detection coupled to liquid chromatography are also reviewed with emphasis on the determination of N-methylcarbamates. The performances of the on-line mass spectrometric detection coupled to solid-phase extraction and liquid chromatography are presented using thermospray, particle beam or electrospray. The main characteristics of the on-line coupling of solid-phase extraction and gas chromatography are also given, with various applications and corresponding detection limits. The recent results obtained with the on-line coupling of gas chromatography with solid-phase micro-extraction are outlined. Supercritical fluid extraction is also mentioned as a new sample handling technique which can be easily on-line coupled to the Chromatographic separation.

Determination of N-methylcarbamates and N-methylcarbamoyloximes in water by high-performance liquid chromatography with the use of fluorescence detection and a single o-phthalaldehyde post-column reaction

A single-stage post-column fluorescence HPLC method for the analysis of N-methylcarbamates and N-methylcarbamoyloximes is presented as an alternative to the traditional two-stage method. The two-stage technique involves post-column hydrolysis with sodium hydroxide followed by derivatization with o-phthalaldehyde and β-mercaptoethanol in a borate buffer. In the proposed method only one reagent, consisting of sodium hydroxide, o-phthalaldehyde, and N,N-dimethyl-2-mercaptoethylamine hydrochloride (Thiofluor), is used. The stability of the reagent is compared to single-stage alternatives involving β-mercaptoethanol or 3-mercaptopropionic acid, which have been previously reported. It is reported that Thiofluor provides the best stability and is satisfactory for overnight chromatographic runs. The sensitivity of the method is reported to be equal to that of the two-stage method. This innovation simplifies reagent preparation and equipment maintenance, while shortening start-up time without any loss in sensitivity.