Malathion detection limits

Azinphos ethyl (h/ f 20-25), malathion (h/ f 40-45) and diazinone (h/ f 47-52) yielded white chromatogram zones on a blue background immediately. Before in situ quantitation the chromatogram was dried in the air until no film of moisture could be seen on the layer surface. It was then dried completely in a stream of warm air whereby the blue coloration of the background changed to brown (Fig. 1). The visual detection limits were 200 ng substance per chromatogram zone. 

O ring. At 20 min inhibition time the detection limits for malathion, parathion methyl and paraoxon were 3, 0.5 and 5pg I respectively. Although these bienzymatic systems look simple, it is difficult to provide optimal conditions for both enzymes. In general the optimum pH, temperature and buffer molarity for different enzymes are different. The experimental conditions are at the levels below the optimum capacity of both enzymes [14], This disadvantage can be minimized by use of a single enzyme system, which is readily inhibited by the pesticide. 

The use of proteins as coatings for the detection of organo-phosphorus compounds was first reported by Van Sant (63). A crystal coated with acetylcholinesterase was used for the detection of DIMP and Malathion, with reported detection limits of 0.4 ppm DIMP and 5 ppb malathion. 

The residues of four pesticides (diazinon, caibaryl, malathion, fenitrothion) were recovered from sesame seeds and baseline resolved on a Cjg column (2 = 225 nm) using a 50/50 acetonitrile/water (0.1% acetic acid) mobile phase [969]. Excellent separation and elution were achieved in 21 min. Linearity was obtained over the range 2-4500 ng/mL with detection limits of 5-50 ng/mL (analyte dependent). 

The phosphorus content offers a sensitive detection mode for fensulfothion, metasystox, disul-foton, methylparathion, folithion, hinosan, malathion, dimethoate, formothion, phosphamidon, phosalone, thiometon, and quinalphos. After development, the plates were heated at 110 C for 2 h, yielding inorganic phosphates. These reacted with anunonium molybdate to give phosphomolybdate. The reduction with ascorbic acid leads to a blue complex with a detection limit of 0.1-0.2 ftg (160). 

Cathodic stripping voltammetry methods have been used in the determination of the OP insecticides Fenitrothion, Malathion " and Methyl Parathion. The influence of selected surfactants on the voltammetric determination of Fenitrothion and Malathion has been studied in detail, " and a new method described for the cathodic electrochemical determination of Methyl Parathion and other OPs using a bismuth film-modified glassy carbon electrode. The electrode behaviour was similar and favourable compared to that of mercury and a bare electrode, and its voltammetric response proportional to the concentration of Methyl Parathion in the 3.0 to lOOng/mL range with a detection limit of 1.2ng/mL. 

Similar other sensors were also reported. In this case one or two enzymes were immobilized on a cellulose triacetate membrane. It was shown that better results were obtained for the determination of pesticides when BChE was used instead of AChE, and a better detection limit was achieved with the esterase present in solution rather than immobilized together with ChOx on the membrane. The fabricated sensor was sensitive to malathion. 

Chitosan-Pmssian blue-multiwall carbon nanotube-hollow gold nanosphere (Chit-PB-MWNT-HGN) films were fabricated to be employed in AChE biosensorsIncorporating MWNTs and HGNs into a Chit-PB hybrid film promoted the electron transfer reaction, enhanced the electrochemical response, and improved the microarchitecture of the electrode surface. Based on the inhibition of the AChE activity by the pesticides malathion, chlorpyrifos, monocrotophos, and carbofuran as model compounds, the biosensor showed a wide dynamic range, low detection limit, good reproducibility, and high stability. Moreover, the AChE/Chit-PB-MWNT-HGN/Au biosensor could also be used for the direct analysis of a practical samples, which would be a new promising tool for pesticide analysis. 

The first field test was successful. Both dimethoate and malathion declined exponentially (Figure 9) and exhibited efficiency factors comparable to the efficiency factors found in the pilot tests. An efficiency factor could be calculated for baygon, but not for diazinon. Some sediment was present into the bottom of the holding tank which could have been slowly releasing baygon and diazinon in the bulk liquid. Nevertheless, after 24 hours of treatment, all pesticides were below the limit of detection. 

The spectrophotometric characteristics of the OPH-CnTPPCi complex are more sensitive to exposure to OPH substrates than those of the OPH-CnTPPSi complex resulting in a lower limit of detection. The characteristic peak for the interaction of CuTPPCi with immobilized OPH is at 412 nm. The absorbance intensity of this peak decreases upon exposure of the surface to diazinon, malathion, conmaphos, and... 

Organophosphate pesticides studied in this work were the model low-toxic OPC trichlorfon, and some common organophosphate pesticides malathion, parathion, dichlorvos, and diazinon (Table I). Calibration curves for these pesticides (dependences of the sensor inhibition response on the analyte concentration) were obtained for all of these OPCs. These calibration curves were obtained under conditions (time of inhibition, pH and temperature) optimize with the model analyte trichlorfon. All of the pesticide calibration curves are similar and Fig. 4 illustrate the method by the example of malathion. The lowest concentration of pesticide samples assayed with 10 min. of incubation of the electrode in inhibitor containing solution was 5 ppb. This resulted in approximately 10 % of the relative inhibition signal. Fig. 4 predicts much better performance of our system compared with the literature data. For example, trichlorfon detection by means of ISFET had a reported limit of detection of ca 250 ppb (5), while conductometric sensor assay registered trichlorfon at ca. 25 ppb (5), still an order of magnitude higher than the described sensor. An amperometric sensor was used to detect dichlorvos with a limit of detection of 350 ppb (2J) and a potentiometric (pH-sensitive) sensor was shown to detect parathion at 39 ppm and diazinon at 35 ppb (9). 

More recently, PONl knockout PONl and PONl transgenic mice have provided important new tools to investigate the role of PONl in modulating OP toxicity. Plasma and liver from PONl mice have no detectable hydrolytic activity toward paraoxon and diazoxon, and have very limited chlorpyrifos-oxonase activity (Shih et al., 1998 Li et al., 2000). PONl mice do not differ from wild-type animals in their sensitivity to demeton-S-methyl, an OP insecticide with a structure similar to malathion and that is not a substrate for PONl (Li et al., 2000). In contrast, PON mice have a dramatically increased sensitivity to chlorpyrifos oxon and diazoxon, and a slightly increased sensitivity to the toxicity of the parent compounds chlorpyrifos and diazinon (Shih et al., 1998 Li et al., 2000). A surprising finding is that the lack of PONl did not affect sensitivity of mice to paraoxon, the substrate for which the enz5une was named, despite the absence of any paraoxonase activity in plasma and liver (Li et al., 2000). 

Tran-Minh et al. have used glass pH electrodes coated with an AChE, acryl-amide/methacrylamide polymer membrane as the internal detector for the pH change. After incubating the electrodes for 1 h in the presence of paraoxon or malathion, the reduced steady-state potentials in buffered aqueous solutions containing ACh could be measured within 8-10 min with low limits of detection... 

Acid phosphatases (Aps) are enzymes with a low pH that catalyze the hydrolysis of orthophosphoric monoester to alcohol and H3PO4. This enzyme has been utilized to a limited extent for the detection of pesticides through inhibition of the enzyme. AP was used with another enzyme, glucose oxidase (GOD), in abi-enzymatic biosensor for the determination of malathion, methyl parathion, and paraoxon. Biocatalytic hydrolysis of glucose-6-phosphate in the presence of acid phosphatase was reversibly... 

An acid phosphatase (AP) hybrid biosensor was developed using a thin layer of potato tissue coupled to an amperometric GOD-based biosensor based on internal sensing of H202. The reversible inhibition of AP was utilized for the determination of malathion, paraoxon methyl, paraoxon, and aldicarb with limits of detection of 0.5 ppb for paraoxon methyl, and 40 ppb for aldicarb. The tissue-based biosensor exhibited a longer shelf life and abetter reliability on the amperometric results than a bi-enzymatic sensor with purified AP and GOD. A similar biosensor was also developed using a potato layer with a Clark-type dissolved oxygen electrode. ... 

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