Abstract: The insecticides are extracted from waters into hexane - CH2Cl2 (17:3) at pH <7 followed by measurement of the HPO emission at 528 nm vs. time in the system previously described (Ibid., 1985, 170, 331). Dicrotophos and dimethoate are measured in the range of 5 to 100 ng of P and malathion and parathion from 10 to 120 ng with detection limits between 0.8 and 2.5 ng. Recoveries are between 73.4 and 98.1% for 50 ng of P with coefficient of variation between 2.5 and 3.4% for 20 ng (n = 8).

Abstract: Acetylcholinesterase was immobilized on amino-terminated magnetic particles and a suspension was pumped into a magnetic reactor of a flow injection manifold. The system was used for enzyme inhibition tests, with a carrier stream of 0.01 M phosphate buffer of pH 8 flowing at 1 ml/min and acetylthiocholine chloride as enzyme substrate. Inhibition constants were obtained for the insecticides carbofuran, paraoxon-ethyl and -methyl and malaoxon and the enzyme activity was determined amperometrically by the oxidation of thiocholine at screen-printed Pt electrodes at a potential of 600 mV. The experimental detection limits were 3-7 µg/l, which agreed with those calculated from the inhibition constants. The results were comparable with those obtained photometrically by the reaction of thiocholine with Ellman's reagent (5,5'-dithiobis-2-nitrobenzoic acid) in the same FIA system. The method was applied to the analysis of insecticides in natural and drinking waters.

Abstract: For determination of the cited groups of insecticides, substrate solution (0.5 mM acetylcholine in 2.5 mM HEPES buffer solution of pH 8.0 containing 20 mM MgCl2, 100 mM NaCl and 0.01% of gelatin; 250 µL) was injected into a carrier stream (0.45 mL min-1) of HEPES buffer solution and the mixture was passed through a 10 cm single bead string reactor containing acetylcholinesterase (I) immobilized on glass beads (0.5 to 0.75 mm). The H+ produced was detected by a pH electrode with a wall-jet entry to assay I activity. Insecticide sample solution was passed through the reactor for 15 min instead of the working buffer. The working buffer was then reintroduced into the carrier line and the substrate solution was injected again to determine I activity. The concentration. of insecticide was determined by the inhibition of enzyme activity. I was reactivated by passing 20 µM 2-pyridine aldoxime methiodide solution through the reactor for 15 to 20 min. The method was applied in the analysis of simulated seawater. Calibration graphs are presented for paraoxon and malathion. Detection limits ranged from 0.5 ppb for malathion to 275 ppb for bromophos-methyl. A flow injection system, incorporating an acetylcholinesterase (AChE) single bead string reactor (SBSR), for the determination of some organophosphorus (azinphos-Et, azinphos-Me, bromophos-Me, dichlorovos, fenitrothion, malathion, paraoxon, parathion-Et, and parathion-Me) and carbamate insecticides (carbofuran and carbaryl) is presented. The detector is a simple pH electrode with a wall-jet entry. Variations in enzyme activity due to inhibition are measured from pH changes when the substrate (acetylcholine) is injected before and after the passage of the solution containing the insecticide. The percentage inhibition of enzyme activity is correlated to the insecticide concentration. Several parameters influencing the performance of the system are studied and discussed. The detection limits of the insecticides ranged from 0.5 to 275 ppb. The determination of these compounds was conducted in Hepes buffer and a synthetic seawater preparation The enzyme reactor can be regenerated after inhibition with a dilute solution of 2-PAM and be reused for analysis. The immobilized enzyme did not lose any activity up to 12 weeks when stored at 4°C.

Abstract: The chopped sample (100 g) was homogenized with methanol, and after filtration and the addition of aqueous 4% Na2SO4, the extract was partitioned with CH2Cl2. The separated CH2Cl2 phase was concentrated to 1 ml, made up to 10 mL with cyclohexane - CH2Cl2 (1:1), and subjected to gel-permeation chromatography on a column (60 cm x 2.5 cm) of Bio-Beads SX-3 resin (200 to 400 mesh). The fraction eluting after 24 min was collected at 5 mL min-1 for 12 min. Crops with high chlorophyll and carotene content were further cleaned up (online) on Nuchar-Celite. The N-methylcarbamates (aldicarb, carbaryl, carbofuran, methiocarb, methomyl, oxamyl and propoxur) and three related metabolites, in methanol, were separated on a column (25 cm x 4.6 mm) of ODS (5 µm), with gradient elution at 1.0 mL min-1 with methanol - water (program given) followed by post-column hydrolysis with NaOH at 95°C to yield methylamine, and derivatization with phthalaldehyde and 2-mercaptoethanol before fluorimetric detection at 455 nm (excitation at 340 nm). Recoveries from 5 different crops fortified at the 0.05- and 0.5 ppm levels averaged 93%. The coefficient of variation were 5% (n = 40) and the detection limits ranged from 5 to 10 ppb.