Solid phase techniques in the extraction of pesticides and related compounds from foods and soils

Trace Level Analysis of Sarin and VX in Food Using Normal Phase Silica Gel and Ultra-Performance Liquid Chromatography-Time-of-Flight Mass Spectrometry (UPLC-TOF-MS)

Ultra-Performance Liquid Chromatography/electrospray ionization mass spectrometry was used for the trace level determination of isopropyl methylphosphonofluoridate (Sarin, GB) and ( O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) after extraction from various foods. A method utilizing normal phase silica gel was developed for the sample preparation and extraction of VX and GB from food. The extraction efficiencies of the normal phase silica gel method for VX was compared to those of other commercial solid phase extraction media and was found to be comparable. Sarin was found to be incompatible with both the mixed mode cation exchange (MCX) sorbents and QuEChERS methods that are commercially available but was successful with the normal phase silica gel method. The linear range of quantitation for VX was 0.1-330 ng/mL and for GB was 20-1200 ng/mL. The average recoveries of VX and GB from the various food matrices along with the corresponding relative standard deviations (RSDs) are reported.

Rapid determination of residual pesticides in tobacco by the quick, easy, cheap, effective, rugged, and safe sample pretreatment method coupled with LC-MS

A quick, easy, cheap, effective, rugged, and safe (QuEChERS) sample pretreatment method coupled with LC-MS was developed for the determination of 11 pesticides in tobacco. Sample pretreatment parameters and instrumental parameters of LC-MS were investigated, and the optimal conditions were selected. Under the optimized conditions, the 11 pesticides were detected simultaneously with a good linear relationship (r(2) = 0.9993-0.9999) and high precisions (less than 5% of the RSD of peak areas). The LODs were in the range of 0.1-5.0 μg/L. Compared with SPE clean-up, QuEChERS greatly simplified the sample pretreatment with simple solvent extraction system. After QuEChERS pretreatment, no serious matrix effects were observed. Used for the analysis of real samples, metalaxyl was found in cigarette and tobacco samples at 63.47 and 132.27 ng/g, respectively. The recoveries for 11 pesticides were in the range of 70.03-118.69%, and RSDs were less than 10%. The proposed method is simple, low cost, and has good reproducibility.

Current trends in solid-phase-based extraction techniques for the determination of pesticides in food and environment

Solid-phase extraction (SPE) procedures for pesticide residues in food and environment are reviewed and discussed. The use of these procedures, which include several approaches such as: matrix solid-phase dispersion (MSPD), solid-phase micro-extraction (SPME) and stir-bar sorptive extraction (SBSE), represents an opportunity to reduce analysis time, solvent consumption, and overall cost. SPE techniques differ from solvent extraction depending on the interactions between a sorbent and the pesticide. This interaction may be specific for a particular pesticide, as in the interaction with an immunosorbent, or non-specific, as in the way a number of different pesticides are adsorbed on apolar or polar materials. A variety of applications were classified according to the method applied: conventional SPE, SPME, hollow-fiber micro-extraction (HFME), MSPD and SBSE. Emphasis is placed on the multiresidue analysis of liquid and solid samples.

Matrix solid phase dispersion-Soxhlet simultaneous extraction clean-up for determination of organochlorine pesticide residues in tobacco

A novel method combining matrix solid phase dispersion (MSPD) with Soxhlet simultaneous extraction clean-up (SSEC) was developed. Being a single-step extraction and clean-up procedure, it could be used instead of multistep solvent extraction and Florisol column clean-up. It not only reduces sample contamination during the procedure, but it also decreases the amount of organic solvent needed. The retention times of standards were used to qualitatively assess the method, and the external standard method was used to quantitatively assess it. Residues of organochlorine pesticides (OCP) in tobaccos were determined by gas chromatography-electron capture detection (GC-ECD), and their identities were confirmed by the standard addition method (SAM). The performance of the method was evaluated and validated: the detection limit was 0.01-0.02 microg g(-1), relative standard deviations were 5-26%, and recoveries were 72-99% at fortification levels of 0.10, 1.00 and 10.0 microg g(-1). The analytical characteristics of MSPD-SSEC compared very favorably with the results from the classical multistep solvent extraction and Florisol column clean-up method.

Optimization of a matrix solid-phase dispersion method for the determination analysis of carbendazim residue in plant material

The objective of this paper was to prove that matrix solid-phase dispersion (MSPD) coupled with high performance liquid chromatography (HPLC) and column switching could be used for the determination and quantification of carbendazim residue in plant samples. By comparing results obtained after optimization of the extraction conditions on an acidic silica gel column, it was determined that sorption and retention of carbendazim were achieved via specific interactions. The method of standard additions was used for quantitative analysis. Its performance was evaluated and validated: the detection limit (UV-Vis detection at lambda=279 nm) was 0.02 microg/g, the relative standard deviations (R.S.D.) were between 2.7 and 4.1% and the recoveries were ranging from 84.3 to 90.7% at the 0.04, 0.08 and 0.1 microg/g fortification levels. The method was successfully tested on cereal samples, and the results obtained with the present off-line MSPD-HPLC procedure were found to compare well with those obtained with procedure involving LLE.

[Residual concentration of hexachlorocyclohexane in a contaminated site in Cidade dos Meninos, Duque de Caxias, Rio de Janeiro, Brazil, after calcium oxide treatment]

Hexachlorocyclohexanes (HCHs) are currently considered potentially carcinogenic to humans. In Brasil, severe soil contamination by HCHs has been identified at Cidade dos Meninos, Duque de Caxias, Rio de Janeiro, where an old HCH factory was abandoned 40 years ago, leaving 1,700 local residents at risk. Calcium oxide treatment was performed on the most heavily contaminated (focus) area. Analysis of superficial soil samples collected years after treatment still showed high residual HCH. Contamination levels as high as 6,200mg/Kg and 7,320mg/Kg were found for alpha- and beta-HCH isomers. For the gamma- and delta-HCH isomers, concentrations reached up to 140mg/Kg and 530mg/Kg, respectively. The results showed that calcium oxide treatment was not efficient to decontaminate the soil in this area.

Solid-phase extraction of quaternary ammonium herbicides

This paper highlights recent advances in the solid-phase extraction (SPE) of quaternary ammonium herbicides in water, soil, plant and biological samples. After a brief introduction summarizing the properties of quaternary ammonium herbicides and the difficulties involved in measuring them, attention is paid primarily to solid supports used for isolation and concentration, pre-treatments required for the different matrices, and eluents applied for quantitative desorption of these analytes. The determination techniques used after SPE and applications of the proposed SPE methodology are also briefly discussed.

Matrix solid-phase dispersion

Matrix solid-phase dispersion (MSPD) is a patented process, first reported in 1989, for conducting simultaneous disruption and extraction of solid and semi-solid samples. MSPD permits complete fractionation of the sample matrix components as well as the ability to selectively elute a single compound or several classes of compounds from the same sample. The method has been applied to the isolation of drugs in food animal tissues but has also found wide application in the analysis of herbicides, pesticides and pollutants from animal tissues, fruits, vegetables and other matrices. The present article provides a review of MSPD applications in these and related fields and discusses the factors known to affect MSPD methods. Both the practical and theoretical aspects of MSPD are also presented.

Determination of abamectin in citrus fruits by liquid chromatography-electrospray ionization mass spectrometry

Liquid chromatography coupled to electrospray mass spectrometry (LC-ES-MS) with positive ion detection was used to determine abamectin in oranges. MS conditions were optimized to achieve maximum sensitivity. The main ion for abamectin was [M+Na]+ at a fragmentor voltage of 180 V. Abundant structural information can be obtained at different fragmentor voltages. The detection limit for the standard solution was 12 pg injected, and good linearity and reproducibility were observed. Abamectin residues were extracted using matrix solid-phase dispersion. Orange samples were homogenized with C18 bonded silica placed onto a glass column and eluted with dichloromethane. Recoveries of the abamectin from oranges fortified with approximately 0.01-10 mg/kg ranged from 94 to 99% with an overall average recovery of 96%. The quantification limit is 0.0025 mg/kg, which means detection limit for this analyte could be set at a few hundred picograms per gram of fruit. The presence in the electrosprayed solution of numerous citrus constituents did not interfere significantly with the ionization process of abamectin. The assay procedure provides a simple, rapid, and sensitive method for monitoring residues in oranges. The method was applied to field treatment orange samples.

Matrix solid-phase dispersion microextraction and determination by high-performance liquid chromatography with UV detection of pesticide residues in citrus fruit

A multiresidue method based on matrix solid-phase dispersion (MSPD) microextraction was studied to determine the carbamate, benfuracarb, and urea insecticides, diflubenzuron, flufenoxuron hexaflumuron and hexythiazox, used in control of citrus pests. Optimisation of different parameters, such as the type of solid support for matrix dispersion, elution solvents and the clean-up step were carried out. The method used 0.5 g of orange sample, C8 bonded silica as MSPD sorbent and dichloromethane as eluting solvent. Recoveries, at spiked concentrations below the maximum residue levels established by Spanish Government, were between 74 and 84% with relative standard deviations ranging from 2 to 4%. The limits of quantification were from 0.15 to 0.25 microgram/g using high-performance liquid chromatography with UV detection at 200 nm. The method may be useful as a screening protocol for the determination of these newly developed pesticides in citrus samples.

Immunosensor for 2,4-dichlorophenoxyacetic acid in aqueous/organic solvent soil extracts

The development of a simple electrochemical immunoassay procedure for the field-based quantification of the herbicide 2,4-D in methanolic soil extracts is presented. The sensor utilizes a competitive immunoassay format incorporating an immobilized antigen complex at the surface of a disposable screen-printed working electrode element. The extent of glucose oxidase-labeled antibody binding to the antigen--electrode is determined amperometrically and is related to sample analyte concentration. The performance of the sensor is assessed in buffer, 30% methanol, and methanolic soil extracts. The device is capable of quantifying 2,4-D in all three matrixes at the low ppm level with coefficient of variation values of 6.2-33.6%. The causes of the variation observed in the sensor response in different soil matrixes are examined and improvements proposed. The sensor, tested in parallel with a commercial 2,4-D immunoassay test kit, yields comparable quantitative data and detection limits while exhibiting greater assay simplicity.

Combination of solid-phase extraction and field-amplified concentration for trace analysis of organonitrogen pesticides by micellar electrokinetic chromatography

An analytical method based on the combination of solid-phase extraction (SPE) and field-amplified concentration (FAC), with micellar electrokinetic chromatography (MEKC) was developed to extract, concentrate, separate, and quantitate six organonitrogen pesticides (metribuzin, bromacil, terbacil, hexazinone, triadimefon, and DEET) in drainage water. The recovery of the first five pesticides was over 85%, and the limit of detection was 0.8 ppb. Four advantages (enhanced enrichment and recoveries, reduced extraction time and interferences) of combining SPE with FAC for trace analysis of pesticides at the ppb level were demonstrated.

Optimization of a matrix solid-phase dispersion method for the analysis of pesticide residues in vegetables

A multiresidue method based on matrix solid-phase dispersion (MSPD) is studied to determine chlorfenvinfos, chlorpyrifos, fenarimol, iprodione, procimydone, propiconazole, tetradifon, triadimefon and vinclozolin in artichokes, green beans, lettuces and tomatoes. Alumina, silica and Florisil were assessed as extracting phases, and the extracts from Florisil were the cleanest. To facilitate manual extraction, sand was added to the sample together with the dispersing phase. Three eluting systems were then studied, and dichloromethane proved to be the best. Further purification can be performed using solid-phase cleanup after diluting extracts with aqueous solutions. Octyl- and octadecyl-silica, modifications of the aqueous diluted extracts and several eluting solvents were studied. Determination was done by capillary gas chromatography (GC) with electron-capture detection, and confirmed by GC-MS using the electron impact mode and the selected ion monitoring. The proposed MSPD method was used to analyze 48 samples taken in the course of a year. Procymidone, vinclozolin, chlorpyrifos and chlorfenvinfos were identified in 10 samples at levels below the maximum residue levels allowed by the Spanish Government.

Determination of pesticide residues in fruit and vegetables

A review concerning the determination of pesticide residues in fruit and vegetables is presented. The basic principles and recent developments in the extraction and quantitation of pesticides are discussed. Consideration is given to solid phase and supercritical extraction techniques, automation and robotic systems, and immunoassay procedures.

Current developments in the analysis of water pollution by polychlorinated biphenyls

A review and discussion of the analytical developments of the last 10 years in the determination of polychlorinated biphenyls (PCBs) in water are presented, including sample treatment, clean-up, identification and determination. Some of the most significant advances have occurred in the area of sample preparation, such as the increased adoption of solid-phase extraction and on-line techniques and the chromatographic separation of PCB congeners, principally by mass spectrometry. Special attention is focused on applications to real samples.

Matrix solid-phase dispersion extraction procedure for multiresidue pesticide analysis in oranges

A multiresidue extraction method based on matrix solid-phase dispersion (MSPD) is optimized for the extraction and gas chromatographic screening of eighteen insecticides (aldrin, carbophenothion, captafol, chlorpyriphos, chlorfenvinphos, diazinon, dicofol, alpha-endosulfan, beta-endosulfan, ethion, fenitrothion, folpet, methidathion, malathion, methyl-azinphos, methyl-parathion, phosmet, and tetradifon) from oranges. After optimization of different parameters, such as type of solid phase used and the amount of solid phase or eluent, recoveries ranged from 67 to 102% with relative standard deviations ranging from 2 to 10%. The limits of detection, calculated as 3 times the baseline noise ranged from 2 to 171 micrograms/kg. These limits of detection were about 10 times lower than the maximum residue levels established by the European Community. Compared with classical methods, the described procedure is simple, less labour intensive and does not require preparation and maintenance of equipment. Troublesome emulsions, such as those frequently observed in liquid-liquid partitioning did not occur.

Organochlorine pesticide analysis in oil seeds and vegetable oil: simplification of silica gel clean-up and elimination of chlorinated solvents

For the determination of organochlorine pesticides (OCPs) in vegetable oils and oil seed samples, a solid-phase extraction method is described, modified from that developed by Steinwandter, with silica gel columns activated with a 10% water content. In comparison to the method developed by Steinwandter, we reduced the amount of solvents and chemicals required for sample preparation and substituted dichloromethane by the much less toxic tert-butylmethyl ether in the eluent mixture. In this manner the sample preparation technique becomes more convenient, cheaper and ecologically more justifiable. Under the specified sample preparation and elution conditions 1 g silica gel retained about 16 mg triglycerides whereas the OCPs were quantitatively eluted. The recoveries for hexachlorobenze, (HCB) alpha-HCH, Lindane (gamma-HCH) gamma-HCH, Heptachlor, Heptachlorepoxid, o,p'-DDE, p,p'-DDE, Dieldrin, o,p'-DDT, p,p'-DDT were between 75 and 90%. The reproducibility of the total method was excellent as well as its ruggedness.