Carbamates methiocarb

APCI can help to reduce matrix effects when analyzing for carbamate insecticides. Eor example, when analyzing for methiocarb in citrus products, the apparent recoveries were in the region of 50% with ESI. However, on changing to APCI, the apparent recoveries were increased to 110%. This is an example where APCI can be an alternative API method if matrix effects are a problem with ESI. It is important to note that the analyte must show sufficient sensitivity to both API techniques. 

Phenylcarbamates, or carbanilates, generally exhibit low water solubilities, and thus they are almost immobile in soil systems. Chlorpropham and Propham are readily volatilized from soil systems, but Terbutol and Carbaryl (Fig. 10, Table 3) are not. Ester- and amide-hydrolysis, N-dealkylation and hydroxylation are among the chemical reactions that carbamates undergo. The N-methylcar-bamate insecticides (Fig. 10, Table 3) commonly used in soils are Carbaryl, Methiocarb,Aldicarb,and Carbofuran [74,173]. 

The general chemical structure of N-methyl carbamate is shown in Fig. 4.4. Common N-methyl carbamates in use today include aldicarb, carbofuran, methiocarb, oxamyl, and carbaryl. N-methyl carbamates share with organophosphates the capacity to inhibit cholinesterase enzymes and, therefore, share similar symptomology during acute and chronic exposure. 

SYNS BAY 9026 BAYER 37344 3,5-DIMETHYL-4-(METHYLTHIO)PHENOL METHYLCARBAMATE 3,5-DIMETHYL-4-METHYL-THIOPHENYL-N-CARBAMAT (GERMAiN) DRAZA ENT 25,726 H 321 MERCAPTODIMETHUR (DOT) MESUROL METHIOCARB METHYL CARBAMIC ACID-4-... 

A method for analysis of polar pesticides in wine by the use of automated in-tube SPME coupled with LC/ESI-MS was proposed (Wu et al., 2002). In-tube SPME is a microextraction and preconcentration technique that can be coupled on-line with high-performance liquid chromatography (HPLC), suitable for the analysis of less volatile and/ or thermally labile compounds. This technique uses a coated open tubular capillary as an SPME device and automated extraction. Using a polypyrrole coating, six phenylurea pesticides (diuron, fluometuron, linuron, monuron, neburon, siduron) and six carbamates (barban, car-baryl, chlorpropham, methiocarb, promecarb, propham) were analyzed in wine. Structures of compounds are reported in Fig. 9.4. Due to the high extraction efficiency of the fiber toward polar compounds, benzene compounds, and anionic species, LODs ranging between 0.01 and 1.2pg/L were achieved, even if the sample ethanol content affects the recoveries of analytes. 

Figure 9.4. Phenylurea pesticides and carbamates detected in wine by automated intube SPME and LC/ESI-MS analysis (Wu et al., 2002). (14) monuron, (15) fluome-turon, (16) siduron, (17) diuron, (18) linuron, (19) neburon, (20) propham, (21) chlorpropham, (22) barban, (23) promecarb (structures of carbaryl and methiocarb are reported in Figs. 9.1 and 9.11, respectively).

The LC/MS positive-ion mode analysis of grape carbamates reported in Fig. 9.11 (carbaryl, carbofuran, diethofencarb, ethiofencarb, fenobu-carb, fenoxycarb, isoprocarb, methiocarb, metholcarb, oxamyl, pirimi-carb, propoxur, and thiobencarb) was performed by matrix solid-phase dispersion (MSPD) extraction using either atmospheric pressure-chemical ionization (APCI) or electrospray ionization (ESI) (Fernandez et al., 2000). 

Figure 9.11. Carbamates determined by LC-atmospheric pressure chemical ionization (APCI) or electrospray (ES) in positive-ion mode (Fern ndez et al., 2000). (24) car-bofuran, (25) ethiofencarb, (26) methiocarb, (27) fenobucarb, (28) isoprocarb, (29) fenoxycarb, (30) diethofencarb, (31) metholcarb, (32) propoxur, (33) pirimicarb, (34) oxamyl, (35) thiobencarb. Structure of carbaryl is reported in Fig. 9.1.

Determination. HPLC comparative tables with recoveries for the different solvents and matrixes are given. MAE was applied to study the thermal degradation of five carbamates some nonpolar and polar pollutants spiked in soil, such as PAHs, PCBs, triazines (atrazine, simazine), and carbamates (propoxur, methiocarb, chlorpropham) subjected to MAE were also studied the recoveries ranged between 70 and 99% with excellent reproducibility, except for carbamates Determination. LC—MS-MS recoveries... 

The U.S.A., through the National Pesticide Survey, " which was organized by the Environmental Protection Agency (US-EPA), established a fist of compounds based on the amount used (>7000 Tons), water solubility (>30 mg/1), and hydrolysis half-life (>25 weeks). The list includes some carbamate pesticides (e.g., aldicarb, propoxur, carbaryl, carbofuran, methiocarb, methomyl, oxamyl, cycloate, butylate, propham, and swep) and various derivatives (e.g., aldicarb sulphone, aldicarb sulphoxide, and 3-hidroxycarbofiiran). In Europe, a list of priority pollutants including pesticides was established in order to protect the environment from the adverse ecological impact of these compounds. ... 

The use of different eluents in LC-RP separations was examined to optimize LC separation and determination of carbamates besides other pesticides by TSP-LC-MS [244]. The effects of additives on LC separation and of the vaporizer temperature on ion formation in TSP-FIA-MS analysis were studied for N-methylcarba-mate [252], carbamates [242] and (thio)carbamates [242] pesticides. A strong reduction in abundance of the characteristic ions [M-tH-CHjNCOj and [M-H-CH3NC0] for methiocarb and its sulone were found because of thermal degradation at 90 °C which made quantitation difficult [252]. The addition of trialkylammo-nium formates increased selectivity and sensitivity, detection limits being < 20 ng in full scan mode [242]. 

The degradation of the carbamates carbofuran and methiocarb in estuarine waters was compared with that of aqueous samples exposed to UV fight in the laboratory. TSP- and ESI-LC-MS were used for product monitoring and identification of degradation products. The predominant degradation pathways observed here. 

Methyl carbamic acid-o-cumenyl ester. See 2-Isopropylphenyl N-methylcarbamate Methyl carbamic acid 2,3-dihydro-2,2-dimethyl-7-benzofuranyl ester. See Carbofuran Methylcarbamic acid-4-(methylthio)-3,5-xylyl ester. See Methiocarb Methyl carbamic acid, 1-naphthyl ester. See Carbaryl... 

Twenty-six methyl carbamate residues and metabolites (e.g., aldicarb-sulfoxide and -sulfone, aldicarb, caibaryl, methiocarb and its sulfoxide and sulfone, etrofolan, baycarb, butocarboxim, thiofanox) were extracted from plant and soil matrices and analyzed as their o-phthalaldehyde derivatives using a C,g column (A = 340 nm, ex 455 nm, em). A 15-min 20/80 80/20 acetonitrile/water gradient was used [972]. 

Carbamates include aldicarb, methiocarb, methomyl, carbofuran, ben-diocarb and oxamyl. Although they are broad-spectrum insecticides, with moderate toxicity and persistence, they rarely bioaccumulate or cause major environmental impacts [25],... 

Methiocarb. This is applied as a rrrirri-pellet for the control of slugs and snails. It is a stomach-acting carbamate. 

Carbamates Phenoxycarb, formethanate, carbaryl, methiocarb, methomyl, propoxur... 

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