Carbamate pesticide detection

Absorbance- and reflectance-based measurements are widespread, as there are many enzymatic reaction products or intermediates that are colored or if not, can react with the appropriate indicator. Sensors using acetylcholinesterase for carbamate pesticides detection are an example of indirect optical fiber biosensors. This enzyme catalyses the hydrolysis of acetylcholine with concomitant decrease in pH41 ... 

A set of qualitative results gained by a prediagnostic (qualitative) biosensor kit (OP-Prot sensor) developed for organophosphate and/or carbamate pesticide detection also arrived for RM08 and RM10. In case of the presence of pesticide mixtures, e.g. as it is the case in most natural samples, the kit detects unselectively the traces of all the present organophosphate and carbamate pesticides. The LOD of the applied kit is 0.1 — 10 pig L-1 depending on the pesticide. 

The anticholinesterase inhibitors (organophosphorous and carbamate), have come into widespread use in the last decades, because they are less persistent in the environment than other pesticides, such as organochlorine. However their presence in water and food is a potential hazard to human health and there is a growing interest in their rapid and accurate determination. Standard methods, based on gas chromatography (GC), are very reliable but there is the need for fast and innovative methods. The use of enzymatic biosensors, and especially electrochemical biosensors, for organophosphorus and carbamate pesticides detection has been reported by many authors [22-26]. 

High performance Hquid chromatography with electrochemical detection has been used to determine 2—7 ppb of carbamate pesticides in water (40). The investigated pesticides were aminocarb, asulam, j -butylphenyknethylcarbamate (BPMC), carbaryl, carbenda2im, chlorpropham, desmedipham, and phenmedipham. 

Detection limits of 250 ng per chromatogram zone have been reported for THC-11-carboxylic acid [15] and of 500 ng per chromatogram zone for carbamate pesticides [19]. 

Chohnesterase-inhibiting pesticides (e g., organophosphate and carbamate pesticides) are detected by dipping the developed chromatogram in a solution of the enzyme chohnesterase followed by incubation for a short period. Then the plate is dipped in a substrate solution, e.g., 1-naphthyl acetate/fast blue salt B. In the presence of the active enzyme, 1-naphthyl acetate is hydrolyzed to 1-naphthol and acetic acid, and the 1-naphthol is coupled with fast blue salt B to form a violet-blue azo dye. The enzyme is inhibited by the pesticide zones, so the enzyme-substrate reaction does not occur pesticides are, therefore, detected as colorless zones on a violet-blue background [36]. 

Mayer, W. J. and Greenberg, M. S., Determination of some carbamate pesticides by high-performance liquid chromatography with electrochemical detection, ]. Chromatogr., 208, 295, 1981. 

J. Besombes, S. Cosnier, P. Labbe, and G. Reverdy, A biosensor as warning device for the detection of cyanide, chlorophenols, atrazine and carbamate pesticides. Anal. Chim. Acta 311, 255—263 (1995). 

A. Ivanov, G. Evtugyn, H. Budnikov, F. Ricci, D. Moscone, and G. Palleschi, Cholinesterase sensors based on screen-printed electrodes for detection of organophosphorus and carbamic pesticides. Anal. Bioanal. Chem. 377, 624-631 (2003). 

L. Pogacnik and M. Franko, Optimisation of FIA system for detection of organophosphorus and carbamate pesticides based on cholinesterase inhibition. Talanta 54, 631-641 (2001). 

A study has been carried out on the determination of triazine and carbamate pesticides and metabolities in seawater by HPLC with photodiode-array detection [393]. 

The pesticides methyl and ethyl parathion were determined in run-off water er preconcentration on XAD-2. This allowed analyses of these compounds at the parts per billion level (497). Parathion and paraoxon obtained from leaf extracts and orchard soil have also been determined (492). The separation of 30 carbamate pesticides by RPC has been described (493). Various modes of postcolumn fluorometric detection of carbamate insecticides have been reported including post-colun)n reaction between o-phthalaldehyde and methylamine, a carbamate hydrolysis... 

Ultraviolet (UV) absorbance has been the most commonly used detection method in HPLC determination of carbamate pesticides (18,61-64). Normally, the absorption maxima occurred at... 

Carbamate pesticides can be determined using different detectors in GC or HPLC analysis. A characteristic feature of a carbamate molecule is the nitrogen atom, which can form the bases for quantitation and some carbamates also contain chlorine, sulfur, or other heteroatoms in the molecule. This allows the use of various detection techniques for their determination (139,140), such as electrical conductivity (165), alkali flame (141) photometry, and mass spectrometry (44,166). 

OP compounds and carbamate are widely used as insecticides, pesticides, and warfare agents [20,21], Detection of pesticides is usually carried out by multiresidue methods (MRMs) of analysis, which are able to detect simultaneously more than one residue and have been developed mainly based on chromatographic techniques. Two groups of MRMs are used (i) multiclass MRMs that involve coverage of residues of various classes of pesticides, and (ii) selective MRMs, which concern multiple residues of chemically related pesticides (e.g., IV-methyl carbamate pesticides (NMCs), carboxylic acids, phenols, etc.). As foods are usually complex matrices all of the pre-analytical steps (matrix modification, extraction, and clean-up) are often necessary. 

Most of the inhibition bioassays or biosensors for organophosphate and carbamate pesticides are based on the amperometric detection of the enzymatic product of the reaction. 

Carbamate pesticides are best analyzed by HPLC using postcolumn deriva-tization technique. Some common carbamate pesticides are listed in Table 2.19.1. Compounds are separated on a C-18 analytical column and then hydrolyzed with 0.05 N sodium hydroxide. Hydrolysis converts the carbamates to their methyl amines which are then reacted with o-phthalaldehyde and 2-mercaptoethanol to form highly fluorescent derivatives. The derivatives are detected by a fluorescence detector. o-Phthaladehyde reaction solution is prepared by mixing a 10-mL aliquot of 1% o-phalaldehyde solution in methanol to 10 mL of acetonitrile containing 100 pL of 2-mercaptoethanol and then diluting to 1 L with 0.05 N sodium borate solution. 

While the depression of plasma and/or RBC cholinesterase may be detected after exposure to very large amounts of carbamates, enzyme activity usually recovers rapidly--within minutes to hours. Hence these tests can be misleading unless one of the rapid methods for testing cholinesterase activity has been employed. A more sensitive and specific absorption test for several of the carbamate pesticides is the measurement of their metabolites in the urine within 48 hours of exposure. Carbamate pesticides are sufficiently acutely toxic that those attending the victim must avoid contact with contaminated apparel or vomitus, and should wear rubber gloves during decontamination of hair and skin of the victim. 

Although an excellent detector for PAEis, the fluorometer is not widely used in environmental analysis, as the number of environmental pollutants with fluorescent spectra is limited. The sensitivity and selectivity of the fluorometer are also used in the A-methyl carbamate pesticide analysis (EPA Method 8318). These compounds do not have the capacity to fluoresce however, when appropriately derivatized (chemically altered), they can be detected fluorome-trically. The process of derivatization takes place after analytes have been separated in the column and before they enter the detector. This technique, called post column derivatization, expands the range of applications for the otherwise limited use of the fluorometer. 

Examination of tissues and excreta from humans or animals for exposure to carbamate pesticides, will almost never result in detection of the parent compound. Exposure assessment of this nature requires determination of metabolitic products, except in extreme situations such as acute poisoning. The most widely used indicator of exposure is probably the determination of urinary phenols (9). 

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