Organophosphorus pesticides sample preparation

Chau and Terry [146] reported the formation of penta-fluorobenzyl derivatives of ten herbicidal acids including 4-chloro-2-methyl-phenoxy acetic acid [145]. They found that 5h was an optimum reaction time at room temperature with pentafluorobenzyl bromide in the presence of potassium carbonate solution. Agemian and Chau [147] studied the residue analysis of 4-chloro-2-methyl phenoxy acetic acid and 4-chloro-2-methyl phenoxy butyric acid from water samples by making the pentafluorobenzyl derivatives. Bromination [148], nitrification [149] and esterification with halogenated alcohol [145] have also been used to study the residue analysis of 4-chloro-2-methyl phenoxy acetic acid and 4-chloro-2-methyl phenoxybutyric acid. Recently pentafluorobenzyl derivatives of phenols and carboxylic acids were prepared for detection by electron capture at very low levels [150, 151]. Pentafluorobenzyl bromide has also been used for the analytical determination of organophosphorus pesticides [152],... 

The mode of injection in GC-based methods can affect the recoveries of diazinon. In a study of the determination of organophosphorus pesticides in milk and butterfat, it was found that the recoveries of diazinon from butterfat, calculated relative to organic solutions of standard compounds, were 125% and 84% for splitless and hot on-column injections, respectively (Emey et al. 1993). Recoveries from milk were not dependent on the mode of injection. It was concluded that the sample matrix served to increase diazinon transfer to the GC column by reducing thermal stress imposed on the analytes and by blocking active sites within the injector. Therefore, on-column injection should be used in order to prevent bias when organic solutions of standard compounds are used for quantitation if this is not possible, the matrix must be present at low concentrations or the calibration standards must be prepared in residue-free samples to avoid unknown bias. 

SFE also would appear to have utility in sample preparation methods. Lopez-Avila et al. (1992) applied SFE to the recovery of a variety of analytes, including organophosphorus pesticides, from solid matrices. The unoptimized extraction from sand gave a recovery of 54% for diazinon. Supercritical trifluoromethane has been shown to extract diazinon from glass beads with a recovery of 86% (Hillmann and Bachmann 1995). Organophosphorus pesticides have also been recovered from Tenax-GC, an adsorbent used to collect diazinon during air sampling, and analyzed directly by GC (Raymer and Velez... 

C Molina, P Grasso, E Benfenati, D Barcelo. Automated sample preparation with extraction columns followed by liquid chromatography-ionspray mass spectrometry. Interferences, determination and degradation of polar organophosphorus pesticides in water samples. J Chromatogr A 737 47-58, 1996. 

Shamsul Hairi, S., Yoshihiro, S., Yoshiaki, K., and Kiyokatsu, J., Solventless sample preparation procedure for organophosphorus pesticides analysis using solid-phase microextraction and online supercritical fluid extraction/high performance liquid chromatography technique. Anal. Chim. Acta, 433, 207-215, 2001. 

The following SPE sorbents have been reported for sample preparation prior to TLC analyses Cg chemically bonded silica gel in the TLC profiling of impurities in MDMA synthesis from piperonal " amino-bonded silica for fractionation of lipid classes" and recovery of lipids from Gaucher and Krabbe s disease patient tissue Cig silica gel for drugs in river water, resveratrol and piceid in wine, " and evolved alachlor collected in ethylene glycol " AgNOg-modified silica gel for determination of docosahexaenoic acid in bovine milk SBD-1 (styrene divinyl benzene) for organophosphorus pesticides in water " and Horisil for two oxycholesterols in raw and cooked meat. ... 

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