Comparison of solid-phase microextraction and stir bar sorptive extraction for determining six organophosphorus insecticides in honey by liquid chromatography–mass spectrometry

Pesticides analysis by liquid chromatography and capillary electrophoresis

Nowadays, a wide range of pesticides are used in agricultural production, and their monitoring in samples of environmental and alimentary interest is of extreme importance to ensure, among others, the safety of consumption of foods. The aim of this work is to provide updated information about the major developments in CE and HPLC in pesticide analysis, covering relevant publications between 2004 and early 2006. The use of different sample pretreatment steps to provide a suitable extraction of these compounds from the different matrices as well as to increase the sensitivity of the determination is also discussed.

Comparative study of the whisky aroma profile based on headspace solid phase microextraction using different fibre coatings

A dynamic headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to ion trap mass spectrometry (GC-(IT)MS) method was developed and applied for the qualitative determination of the volatile compounds present in commercial whisky samples which alcoholic content was previously adjusted to 13% (v/v). Headspace SPME experimental conditions, such as fibre coating, extraction temperature and extraction time, were optimized in order to improve the extraction process. Five different SPME fibres were used in this study, namely, poly(dimethylsiloxane) (PDMS), poly(acrylate) (PA), Carboxen-poly(dimethylsiloxane) (CAR/PDMS), Carbowax-divinylbenzene (CW/DVB) and Carboxen-poly(dimethylsiloxane)-divinylbenzene (CAR/PDMS/DVB). The best results were obtained using a 75 microm CAR/PDMS fibre during headspace extraction at 40 degrees C with stirring at 750 rpm for 60 min, after saturating the samples with salt. The optimised methodology was then applied to investigate the volatile composition profile of three Scotch whisky samples--Black Label, Ballantines and Highland Clan. Approximately seventy volatile compounds were identified in the these samples, pertaining at several chemical groups, mainly fatty acids ethyl esters, higher alcohols, fatty acids, carbonyl compounds, monoterpenols, C13 norisoprenoids and some volatile phenols. The ethyl esters form an essential group of aroma components in whisky, to which they confer a pleasant aroma, with "fruity" odours. Qualitatively, the isoamyl acetate, with "banana" aroma, was the most interesting. Quantitatively, significant components are ethyl esters of caprilic, capric and lauric acids. The highest concentration of fatty acids, were observed for caprilic and capric acids. From the higher alcohols the fusel oils (3-methylbutan-1-ol and 2.phenyletanol) are the most important ones.

Films coated with molecular imprinted polymers for the selective stir bar sorption extraction of monocrotophos

The flexibility and simplicity of stir bar sorption extraction (SBSE) have been combined with the selectivity of molecularly imprinted polymers (MIP). Stir bars were coated reproducible with a 180 microm film formed from a formic acid solution of nylon-6 polymer either nonimprinted or imprinted with monocrotophos. Time sorption profiles were measured for the extraction of monocrotophos from dichloromethane at the concentration of 10-200 micromol/L levels with both types of films in order to compare extraction characteristics. The results indicated that the MIP coated layer showed remarkable high affinity toward monocrotophos and equilibrium adsorption was attained rapidly (60 min) in contrast to free standing molecularly imprinted polymer in which equilibrium adsorption was normally attained after several hours. The stir bars coated with MIP films were capable of extracting four structural analogues of monocrotophos from dichloromethane solution, which suggests that both the amino group and PO part of these molecules is responsible for interaction with the imprinted polymer. Evidence was also presented by FT-IR analysis that the amide-hydrogen-bonding interaction between the MIP-coated films and monocrotophos was originated for monocrotophos recognition. To achieve selective extraction of monocrotophos from sample, stir bars coated with MIP films were washed with 10% (v/v) acetic acid/methanol and methanol. Clean extracts and yields of 95% were obtained, demonstrating the suitability of stir bar coated with MIP films for the analysis of environmental and biological samples. Compared with traditional MIP and SBSE, the MIP-coated film showed not only the high selectivity but also the rapid equilibrium adsorption.

Comparison of stir bar sorptive extraction and membrane-assisted solvent extraction as enrichment techniques for the determination of pesticide and benzo[a]pyrene residues in Brazilian sugarcane juice

The present work compares two modern and environmentally friendly enrichment techniques, stir bar sorptive extraction (SBSE) and membrane-assisted solvent extraction (MASE) for the determination of 18 organic contaminant residues in Brazilian sugarcane juice. Stir bar sorptive extraction and thermal desorption coupled to capillary gas chromatography-mass spectrometry using the selected ion monitoring mode [SBSE-TD-GC-MS(SIM)] and membrane-assisted solvent extraction combined with large volume injection [MASE-LVI-GC-MS(SIM)] methods were assessed taking into account the time of extraction [SBSE (3h) and MASE (30min)], the recoveries [SBSE (0.2-55.3%) and MASE (13.6-103.1%)], the repeatability [SBSE (0.3-19.2%) and MASE (2.6-18.4%)] and the limits of detection [SBSE (0.002-0.71 microgL(-1)) and MASE (0.004-0.56 microgL(-1))] of the selected triazine, organochlorine and organophosphorus pesticides as well as benzo[a]pyrene in sugarcane juice. In general, faster analyses and much better analyte recovery results were achieved with MASE, whereas greater sensitivity and repeatability were obtained with SBSE. SBSE and MASE procedures were applied to the analysis of six sugarcane juice samples from the city São Carlos, in the state of São Paulo, Brazil. A comparison of the results of the pesticide and benzo[a]pyrene residues at microgL(-1) level obtained by the two methods showed good agreement.

Development and Application of Porous Membrane-Protected Carbon Nanotube Micro-Solid-Phase Extraction Combined with Gas Chromatography/Mass Spectrometry

A novel, multiwalled carbon nanotube (MWCNT)-supported micro-solid-phase extraction (mu-SPE) procedure has been developed. A 6-mg sample of MWCNTs was packed inside a (2 cm x 1.5 cm) sheet of porous polypropylene membrane whose edges were heat-sealed to secure the contents. The mu-SPE device, which was wetted with dichloromethane, was then placed in a stirred sewage sludge sample solution to extract organophosporous pesticides, used here as model compounds. Tumbling of the extraction device within the sample solution facilitated extraction, and the porous membrane acted as a filter to exclude the extraction of extraneous materials. After extraction, analytes were desorbed in hexane and analyzed using gas chromatography/mass spectrometry. Since the porous membrane afforded protection of the MWCNTs, no further cleanup of the extract was required. The pi-pi electrostatic interaction with the analytes and the large surface area of MWCNTs facilitated the adsorption of analytes, with good selectivity and reproducibility. Under the optimized extraction conditions, the method showed good linearity in the range of 0.1-50 mug/L, repeatability of the extractions (RSD 2-8%, n = 4), and low limits of detection (1-7 pg/g). No analyte carryover effect was observed, and each mu-SPE device could be used for up to 30 extractions. Comparison was made with hollow fiber protected solid-phase microextraction and headspace solid-phase microextraction; mu-SPE was demonstrated to be a fast, accurate, and cost-effective pretreatment method for sewage sludge samples.

Optimisation of stir bar sorptive extraction applied to the determination of volatile compounds in vinegars

Stir bar sorptive extraction (SBSE) was evaluated for analysing volatile compounds in vinegar. The extraction and desorption analytical conditions have been optimised using a two-level factorial design expanded further to a central composite design. This chemometric tool is very appropriate in screening experiments where the aim is to investigate several possibly influential and/or interacting factors. For the extraction step, the optimum analytical conditions were: sample volume 25 ml without dilution, sampling time 120 min, NaCl content 5.85 g, and stirring speed 1250 rpm. For the desorption step, the optimised analytical conditions were: desorption temperature 300 degrees C, cryofocusing temperature -140 degrees C, flow of helium 75 ml min(-1), and desorption time 10 min. The SBSE procedure developed shows detection limits, and linear ranges adequate for analysing this type of compounds. The repeatability values obtained were lower than 10%. SBSE is a very simple, solvent-free, fast technique with better sensitivities, in general, than SPME. However, a disadvantage of this technique is that, up to now, the stir bar offers a limited enrichment capability for polar compounds because is only available with PDMS coating.

Recent developments in solid-phase microextraction coatings and related techniques

During the last decade, solid-phase microextraction (SPME) has gained widespread acceptance for analyte matrix separation and preconcentration. Relatively few data are currently available dealing with in-house production of fibres with tailor-made properties to be used for SPME, though recently the number of publications evaluating new coatings has been considerably growing. This review, centred on publications that appeared during the last five years, is resuming different approaches which can be used for fibre production and further summarises alternative techniques closely related to SPME, such as in-tube extraction or single-drop microextraction (SDME). The aim is to give the reader a concise overview of recent developments in new coating procedures and materials, including the respective applications.

Stir-bar sorptive extraction and thermal desorption-ion mobility spectrometry for the determination of trinitrotoluene and l,3,5-trinitro-l,3,5-triazine in water samples

Stir-bar sorptive extraction (SBSE) is interfaced to ion mobility spectrometry (IMS) for the rapid detection of trace analytes, with the explosives, trinitrotoluene (TNT) and l,3,5-trinitro-l,3,5-triazine (RDX) shown as examples. SBSE retains its inherent advantages as a sensitive, straightforward, solventless, and inexpensive method. Additionally, the new SBSE-IMS technique exhibits excellent sensitivity, has onsite field analysis capabilities and provides the potential to detect and quantitate analytes that are difficult to accomplish using gas chromatography (GC) or high-performance liquid chromatography (HPLC). The SBSE-IMS technique is shown to be an effective method for the low-level detection of TNT and RDX from water with method standard deviation of 8.6% for TNT and 6.6% for RDX. The short desorption time of 60 s and analysis time of less than 20 ms along with limits of detection of 0.1 ng/mL for TNT and 1.5 ng/mL for RDX and render the method potentially useful for trace analysis. Desorption profiles showing the kinetics of analyte transfer from the stir-bar into the IMS are shown and discussed; the SBSE-IMS configuration shows very rapid desorption from the stir-bar, with the analytes completely transferred in most cases, in under 1 min.

Novel stir bar sorptive extraction methods for environmental and biomedical analysis

Stir bar sorptive extraction (SBSE) is sample preparation technique that involves the extraction and enrichment of organic compounds from a liquid sample. The technique is based on the principle of sorptive extraction. A large amount of extraction phase is coated on a stir bar. An analyte is extracted into the extraction phase, based on its octanol-water partitioning coefficient and the phase ratio. Recently, various methods involving SBSE were developed in order to further facilitate analysis and improve sensitivity. In this review, we focused on the novel methods that involve SBSE with in situ derivatization, SBSE with in situ de-conjugation, thermal desorption (TD) in the multi-shot mode and TD with in tube derivatization method. Those methods were applied successfully to the trace analysis of environmental and biological samples and extremely low detection limits were achieved.

Determination of carbamates and organophosphorus pesticides by SDME–GC in natural water

Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. Analytical methods with low quantification limits are necessary. The application of a new extraction technique, solvent drop microextraction (SDME), followed by gas chromatography with a nitrogen-phosphorus detector, was assessed for determining carbamates and organophosphorus pesticides in natural water. Experimental parameters which control the performance of SDME such as selection of microextraction solvent, optimization of organic drop volume, effects of sample stirring, salt addition, and, finally, sorption time profiles were studied. Once SDME was optimized, analytical parameters such as linearity (r 2>0.99), precision (<13%), and detection limits (0.2 to 5 microg/L), plus matrix effects were evaluated (no matrix effects were found). SDME is a dynamic technique able to extract pesticides from water in 14 min; the use of organic solvents and water samples for SDME is negligible compared to other extraction techniques.

Optimization of a multi-residue screening method for the determination of 85 pesticides in selected food matrices by stir bar sorptive extraction and thermal desorption GC-MS

A multi-residue method to determine 85 pesticides, including organochlorine pesticides, carbamates, organophosphorus pesticides, and pyrethroids, in vegetables, fruit, and green tea, has been developed. The method is based on stir bar sorptive extraction (SBSE) coupled to thermal desorption (TD) and retention time locked (RTL) GC-MS operating in the scan mode. Samples are extracted with methanol and diluted with water prior to SBSE. Dilution of the methanol extract before SBSE was optimized to obtain high sensitivity and to minimize adsorption onto the glass wall of the extraction vessel as well as to minimize sample matrix effects (particularly for the pesticides with high log K(o,w) values). The optimized method consists of a dual SBSE extraction performed simultaneously on respectively a twofold and a fivefold diluted methanol extract. After extraction, the two stir bars are placed in a single glass thermal desorption liner and are simultaneously desorbed. The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection: < 5 microg kg(-1)) for most of the target pesticides. The method was applied to the determination of pesticides at low microg kg(-1) in tomato, cucumber, green soybeans, spinach, grapes, and green tea.

Capillary electrophoresis for analyzing pesticides in fruits and vegetables using solid-phase extraction and stir-bar sorptive extraction

Two procedures based on solid-phase extraction (SPE) and stir-bar sorptive extraction (SBSE) in combination with micellar electrokinetic chromatography (MEKC)--diode array detection (DAD) were compared for the simultaneous extraction of acrinathrin, bitertanol, cyproconazole, fludioxonil, flutriafol, myclobutanil, pyriproxyfen, and tebuconazole in lettuce, tomato, grape, and strawberry. Selectivity and resolution of the MEKC procedure were studied changing the pH and the molarity of the buffer, the type and the concentration of surfactant, and the methanol content in the mobile phase. A buffer consisting of 6 mM sodium tetraborate decahydrate with 75 mM of cholic acid sodium solution (pH 9.2) gave the best results. Linearity, extraction efficiencies and limits of quantitation (LOQs) of both extraction methods were compared. The recoveries obtained by SPE ranged from 40 to 106% with relative standard deviations (R.S.D.s) from 10 to 19% whereas by the SBSE method, the recoveries were 12-47% and the R.S.D.s 3-17%. The LOQs were much better by SPE (0.2-0.5 mg kg(-1) depending on the processed sample amount) than those obtained by SBSE (1 mg kg(-1) for each compound). Advantages and disadvantages of both procedures are also discussed. As SPE is more robust, rapid, and sensitive than SBSE, its application in combination with MEKC is recommended because provided LOQs below the MRLs established, which is not always attained by SBSE.

Determining pirimiphos-methyl in durum wheat samples using an acetylcholinesterase inhibition assay

An electrochemical assay used for detecting acetylcholinesterase (AChE) inhibitors has been optimised to detect pirimiphos-methyl in durum wheat. Pirimiphos-methyl is a phosphothionate insecticide and so it needs to be transformed into the corresponding oxo form to act as an effective AChE inhibitor. The inhibition assay was based on the electrochemical detection of the product of AChE, choline, via choline oxidase biosensors obtained with Prussian-Blue modified screen printed electrodes. The procedure for the oxidation of pirimiphos methyl via N-bromosuccinimide (NBS) and AChE inhibition was optimised for reagent concentrations and inhibition time in a buffer solution. A calibration of the pirimiphos-methyl (25-1,000 ng/ml) was obtained in the buffer. The intra-electrode CV ranged between 1.6 and 15.0, whereas the inter-electrode CV ranged between 4.6 and 16.0. The detection limit (LOD) was 38 ng/ml, and the I(50%) was 360 ng/ml. The assay conditions were then re-optimised to work with durum wheat extracts, and the calibrations were obtained under different experimental conditions, such as sample pretreatment (milled or whole grains) and extract concentration. The calibrations were slightly affected by the sample matrix, resulting in an increased LOD (65-133 ng/ml) and I(50%) (640-1,650 ng/ml). The LOD found for the sample, determined under optimal conditions, was 3 mg/kg. Spiked samples were prepared at the EU regulated level (5 mg/kg) and analysed with the optimised protocol, resulting in an average recovery of 70.3%.

Determination of pesticides and PCBs in honey by solid-phase extraction cleanup followed by gas chromatography with electron-capture and nitrogen?phosphorus detection

A multiresidue method for determination of 15 organochlorine pesticides (OCPs), six polychlorinated biphenyls (PCBs), and seven organophosphorus pesticides (OPPs) is implemented for routine determinations of residues in honey. The method involves solid-phase extraction cleanup and determination by GC-ECD/NPD. Quantitation limits ranged from 0.1 to 0.6 microg kg-1 honey for OCPs and PCBs, and from 5.0 to 25.0 microg kg-1 honey for OPPs. Recoveries of OCPs ranged between 77.4 and 94.0%; for PCBs they were from 63.8 to 73.5%. Recovery assays for OPPs varied from 66.7 to 98.1%. The method was applied to the analysis of 111 honey samples from Aragon, Spain. The results obtained indicated a low level of contamination by pesticide residues and PCBs, which can contribute to ensuring the consumer has a safe wholesome supply of honey.

Analysis of endocrine disrupting alkylphenols, chlorophenols and bisphenol-A using hollow fiber-protected liquid-phase microextraction coupled with injection port-derivatization gas chromatography–mass spectrometry

Liquid-phase microextraction (LPME) coupled with gas chromatography-mass spectrometry were used to determine alkylphenols (APs), chlorophenols (CPs) and bisphenol-A (BPA) in aqueous samples. APs, CPs and BPA are highly polar compounds and need to be derivatized before analysis by GC-MS. In this work, they were derivatized in the GC injection port with bis(trimethylsilyl)trifluoroacetamide (BSTFA). The analytes were extracted directly from 5 ml of sample solution using 5 microl of organic solvent though a porous polypropylene hollow fiber. The hollow fiber, filled with an immiscible organic solvent (ca. 5 microl), was immersed in the sample solution which was stirred during the 30-min extraction. An aliquot (2 microl) of the extract and 2 microl of BSTFA were then consecutively injected into the GC injection port. Extraction parameters such as extraction time, pH of sample, concentration of salt added, and stirring rate were optimised. The proposed LPME provided a good average enrichment factor of up to 162-fold, reproducibility ranging from 5.9 to 13.9% (n = 4), and good linearity (r2 = 0.995) for spiked water samples. The limits of detection (LODs) ranged between 0.005 and 0.015 microgl(-1) (S/N = 3) using GC-MS with selective ion monitoring and limits of quantification were in the range of 0.012-0.026 microg l(-1). A comparative study was performed between LPME, headspace solid-phase microextraction (HS-SPME) and liquid-liquid extraction (LLE). The results obtained suggested that hollow fiber LPME was a rapid, simple and efficient technique for APs, CPs and BPA, and provided a good alternative to SPME and LLE. Finally, the proposed method was applied to monitor Singapore coastal water samples.

Evaluation of solid-phase extraction and stir-bar sorptive extraction for the determination of fungicide residues at low-μgkg−1 levels in grapes by liquid chromatography–mass spectrometry

A liquid chromatography-mass spectrometry method has been developed for determining bitertanol, carboxin, flutriafol, pyrimethanil, tebuconazole and triadimefon. The evaluation of both atmospheric pressure interfaces (API), atmospheric pressure chemical ionization (APCI) and electrospray (ESI) using positive and negative ionization modes, clearly shows that the studied pesticides are more sensitive using APCI in positive mode. Two procedures based on solid-phase extraction (SPE) and stir-bar sorptive extraction (SBSE) have been assessed for extracting these compounds in grape. The recoveries obtained by SPE in samples spiked at the limit of quantification (LOQ) level ranged from 60 to 100% with relative standard deviation (R.S.D.s) from 7 to 17%. With the SBSE the recoveries obtained from samples spiked at LOQ level were between 15 and 100% and the R.S.D.s between 10 and 19%. The LOQs of most compounds are better by SPE (0.003-0.01 mg kg(-1)) than by SBSE (0.01 mg kg(-1) for all fungicides). Although SPE provided higher recoveries, lower R.S.D.s, best LOQs and is more rapid to carry out compared with SBSE, this last one has some advantages such as lower organic solvent consumption, and cleaner extracts. Results obtained applying both techniques to real samples are analogous.