Supercritical-fluid extraction of synthetic pyrethroids from wool

A stepwise approach was used to develop a supercritical fluid extraction (SFE) method for analysis of synthetic pyrethroids (SPs) on a wool matrix, commencing with a simple inert matrix to examine the solubility of the pyrethroids in the extraction fluid CO(2) and then extended to the real wool matrix. Chemometric approaches were used to determine the SFE optimum conditions. It was found that pyrethroids were readily extractable from an inert matrix over a wide range of pressure (170-350 atm) and at low temperature (<90 degrees C). Subambient hexane efficiently trapped the compounds from the depressurised fluid. Excessively high pressure and temperature resulted in poor trapping, isomerisation and possibly degradation of some components. With spiked wool samples method modifications focused on reducing the coextraction of grease, a bulk matrix component of raw wool. By using alumina (containing 8% moisture) and operating the extraction at 50 degrees C, 200 atm for 60 min, sufficiently clean extracts of pyrethroids suitable for gas chromatography-electron-capture detection analysis were obtained. The recoveries of all SPs were satisfactory (78-101%) over the range of 0.5-5 microg/g levels of these compounds. The precision of the entire analysis procedure was comparable to the conventional Soxhlet extraction method. Detection limits of some commonly used SPs for sheep treatment were also evaluated. Comparable results relative to those achieved by solvent extraction for incurred wool samples were obtained with a recovery of 81-85%. The results, however, suffered high uncertainties (R.S.D. approximately 19-24%) due to the small amount of wool sample taken in each extraction and the suspected inhomogeneity of the wool. Different persistences of cypermethrin isomers in wool were observed.

Automated one-step supercritical fluid extraction and clean-up system for the analysis of pesticide residues in fatty matrices

An automated supercritical fluid extraction and in-line clean-up system has been developed for organochlorine and organophosphate pesticide residues contained in fats. This procedure utilizes supercritical carbon dioxide modified with 3% acetonitrile at 27.58 MPa and 60 degrees C to extract and separate the pesticide residues from the fat on a C1 bonded phase preparative column at 95 degrees C. The automated C1 system recovers 86 of 117 nonpolar to moderately polar organochlorine and organophosphate pesticides from fats. Ten of the 31 pesticides not recovered through the system are not recovered through the conventional clean-up sorbent, Florisil. Pesticide residues can be separated from 0.68 g of butter fat and 0.67 g corn oil, resulting in 2.9 mg of butterfat and 2.1 mg corn oil residue co-eluting into the pesticide fraction. Also, this integrated method can extract and clean-up a 5 g sample of fatty foods containing < 18% fat and 70% moisture. The automated C1 system is reproducible and the amount of co-extracted sample residue in the pesticide fraction yields results comparable to the current methodology, which uses organic solvent extraction and gel permeation chromatography, along with a final Florisil column clean-up step. This automated C1 system simplifies the extraction and clean-up step while reducing solvent usage and hazardous waste.

Determination of organophosphorus pesticides in wheat flour by supercritical fluid extraction and gas chromatography with nitrogen-phosphorus detection

Application of supercritical fluid extraction (SFE) for selective isolation of organophosphorus pesticides from a real-world matrix (wheat flour) has been described. The method uses extraction with supercritical carbon dioxide at 206.8 bar and 60 degrees C, followed by quantitation by gas chromatography with nitrogen-phosphorous detection without clean-up of the extracts. Comparison of SFE with a method currently employed for sample preparation (i.e., organic solvent extraction followed by liquid-liquid extraction and gel permeation chromatography clean-up) shows that the SFE technique simplifies the sample preparation step and speeds up the determination of organophosphorus pesticides in flour. Extraction times were 60 min for a 7 g sample size. This technique was able to determine organophosphorus pesticides (ethoprophos, diazinon, chlorpyrifos methyl, fenitrothion, parathion, phenthoate, EPN) in samples at the 10 ng/g level.

Experimental design approach for the optimization of supercritical fluid extraction of chlorophenols from polluted soils

Supercritical fluid extraction and liquid chromatography-electrochemical detection (LC-ECD) were used to the determination of chlorophenols in contaminated soil samples. Full factorial design experiments were used in order to optimize the extraction parameters: pressure, extraction cell temperature and percentage of modifier. Pressure and percentage of modifier (methanol) had statistically significant effects on the recovery of the chlorophenols. Good repeatability (4.9-11.8%) and reproducibility (4.9-12.5%) were achieved and low detection limits (3-150 ng g-1) were obtained. The method was validated by comparing the results with those obtained in a European intercomparison exercise.

Official multiresidue methods of pesticide analysis in vegetables, fruits and soil

Many different types of pesticides are used extensively on fruits and vegetables. The present contribution represents an overview of the multiresidue methods of analysis of the most widely used pesticides.