PhD: HPLC methods development for quantitative determination of some herbicides and organophosphate insecticides in various matrices

Lenče Velkoska-Markovska
Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, Skopje, Macedonia
October, 2013
 

Abstract

The research presented in this work is contribution in the field of new analytical methods for identification and quantification of some herbicides (2,4-D and atrazine) and organophosphorus insecticides (malathion, parathion and fenitrothion) and their residues in various matrices. The development of relatively fast, simple, precise and accurate HPLC methods using ultraviolet diode array detector (UV-DAD) for the determination of pesticide residues in apple juice and water samples are explored. Furthermore, the new HPLC methods for quantitative determination of the active ingredients 2,4-D and malathion in the pesticide formulations Monosan Herbi, DMA-6 and Etiol tečni are developed.

For development of reversed-phase liquid chromatographic methods five analytical columns with different dimensions and particle size are used (LiChrospher 60 RP-select B (125 mm x 4 mm; 5 μm), LiChrospher 60 RP-select B (250 mm x 4 mm; 5 μm), Purospher STAR RP-8e (30 mm x 4 mm; 3 μm), Purospher STAR RP-18e (30 mm x 4 mm; 3 μm) and Poroshell 120 EC-C18 (50 mm x 3 mm; 2,7 μm)), while the developing of the normal-phase chromatographic methods is carried out using the intermediate column LiChrosorb CN (250 mm x 4 mm; 5 μm).

For quantitative determination of the active ingredient 2,4-D in the pesticide formulations Monosan Herbi and DMA-6, four reversed-phase (RP) liquid chromatographic methods are developed. Four RP-HPLC methods and one NP-HPLC method are proposed for determination of the active ingredient malathion in the pesticide formulation Etiol tečni. Five RP-HPLC methods for determination of residues of atrazine, malathion, parathion and fenitrothion in apple juice samples, and for determination of residues of 2,4-D, atrazine, malathion, parathion and fenitrothion in water samples, and one NP-HPLC method for determination of residues of parathion, malathion and fenitrothion in apple juice samples are developed. For enrichment and clean-up of compounds of interest Supelclean ENVI-18 SPE tubes were used.

The optimal conditions for separation and quantitative determination of the analytes with isocratic elution are obtained using mobile phases consisting of different ratios of acetonitrile/water in reversed-phase mode and n-hexane/dichloromethane in normal-phase mode, flow rate of 1 mL/min, constant column temperature of 25 °C and UV detection at 220 nm and 270 nm.

To determine the most effective procedure for the extraction of the investigated pesticides from water samples several organic solvents are tested: dichloromethane, a mixture of n-hexane-acetone (4:1, V/V), diethyl ether and petrolbenzene.

The validation of the developed methods is performed by testing the following parameters: specificity, selectivity, linearity, precision, accuracy, limit of detection and limit of quantification. Retention and separation factor, resolution, coefficients of determination, relative standard deviation of the results for retention time, the peak area and peak height, recovery of analytes and active ingredients quantity in the pesticide formulations, apple juice and water samples for each method are determined.