Applications of solid-phase microextraction in food analysis

Food analysis is important for the evaluation of the nutritional value and quality of fresh and processed products, and for monitoring food additives and other toxic contaminants. Sample preparation, such as extraction, concentration and isolation of analytes, greatly influences the reliable and accurate analysis of food. Solid-phase microextraction (SPME) is a new sample preparation technique using a fused-silica fiber that is coated on the outside with an appropriate stationary phase. Analyte in the sample is directly extracted to the fiber coating. The SPME technique can be used routinely in combination with gas chromatography (GC), GC–mass spectrometry (GC–MS), high-performance liquid chromatography (HPLC) or LC–MS. Furthermore, another SPME technique known as in-tube SPME has also been developed for combination with LC or LC–MS using an open tubular fused-silica capillary column as an SPME device instead of SPME fiber. These methods using SPME techniques save preparation time, solvent purchase and disposal costs, and can improve the detection limits. This review summarizes the SPME techniques for coupling with various analytical instruments and the applications of these techniques to food analysis.     

Hollow fiber membrane-protected solid-phase microextraction of triazine herbicides in bovine milk and sewage sludge samples

A porous polypropylene hollow fiber membrane (HFM)-protected solid-phase microextraction (HFM-SPME) procedure in conjunction with gas chromatography/mass spectrometric analysis for use in the determination of triazine herbicides in bovine milk samples is described. A 65-microm polydimethylsiloxane-divinylbenzne (PDMS-DVB) SPME fiber was protected by an HFM. HFM-SPME experimental parameters such as fiber type, extraction time, extraction temperature and salt concentration were investigated and optimized. The relative standard deviations for the reproducibility of the optimized HFM-SPME method varied from 4.30 to 12.37%. The correlation coefficients of the calibration curves were between 0.9799 and 0.9965 across a concentration range of 0-200 microg l(-1). The method detection limits for triazines in bovine milk were in the range of 0.003-0.013 microg l(-1) and limits of quantification were in the range of 0.006-0.021 microg l(-1). The suitability of HFM-SPME was extended to the analysis of the herbicides in sewage sludge samples. The results demonstrate that HFM-SPME was an efficient pretreatment and enrichment procedure for complex matrices.     

Factors affecting multiresidue determination of priority herbicides when using solid-phase microextraction

A solid-phase microextraction (SPME) procedure was developed for the determination of 10 selected organonitrogen herbicides (s-ethyl dibropylthiocarbamate [EPTC], molinate, propachlor, trifluralin, simazine, atrazine, propazine, terbuthylazine, alachlor, and prometryn) and was tested with various natural waters. Gas chromatography coupled with flame thermionic and mass spectrometric detection was used for quantitation. For this purpose, polydimethylsiloxane and polyacrylate fibers were used and the factors affecting the SPME process such as pH, ionic strength, methanol content, memory effect, stirring rate, and adsorption-time profile were investigated and optimized. By using spiked liquid chromatography water, optimal factors were determined to be 25% salt, <0.5% methanol, stirring rate of 960 rpm, pH 4, and an equilibrium time of 30 min. These conditions were used in further studies of the fibers and in analysis of natural water samples. The method was applied to spiked natural waters such as ground water, sea water, lake water, and river water at a concentration range of 0.5-10 microg/L. Limits of detection ranged from 5 to 90 ng/L, and precision ranged from 5 to 15% (as relative standard deviation), depending on the pesticide, fiber, and detector used. The recoveries of herbicides were 70.2-118.4%, and the average r2 values of the calibration curves were >0.99 for all analytes. The results demonstrate the suitability of the SPME method to determine these organonitrogen herbicides in various natural waters. River water samples originating from the Epirus region (Northwestern Greece) were analyzed to verify the performance of the optimized method by comparing the results obtained by SPME with those obtained by using conventional solid-phase extraction of the selected herbicides.     

Determination of organochlorine pesticides in water using microwave assisted headspace solid-phase microextraction and gas chromatography

A coupled technique, microwave-assisted headspace solid-phase microextraction (MA-HS-SPME), was investigated for one-step in situ sample pretreatment for organochlorine pesticides (OCPs) prior to gas chromatographic determination. The OCPs, aldrin, o,p'-DDE, p,p'-DDE, o,p'-DDT, p,p'-DDT, dieldrin, alpha-endosulfan, beta-endosulfan, endosulfan sulfate, endrin, delta-HCH, gamma-HCH, heptachlor, heptachlor epoxide, methoxychlor and trifluralin were collected by the proposed method and analyzed by gas chromatography with electron-capture detection (GC-ECD). To perform the MA-HS-SPME, six types of SPME fibers were examined and compared. The parameters affecting the efficiency in MA-HS-SPME process such as sampling time and temperature, microwave irradiation power, desorption temperature and time were studied to obtain the optimal conditions. The method was developed using spiked water samples such as field water and with 0.05% humic acid in a concentration range of 0.05-2.5 microg/l except endosulfan sulfate in 0.25-2.5 microg/l. The detection was linear over the studied concentration range with r2>0.9978. The detection limits varied from 0.002 to 0.070 microg/l based on S/N=3 and the relative standard deviations for repeatability were <15%. A certified reference sample of OCPs in aqueous solution was analyzed by the proposed method and compared with the conventional liquid-liquid extraction procedure. These results are in good agreement. The results indicate that the proposed method provides a very simple, fast, and solvent-free procedure to achieve sample pretreatment prior to the trace-level screening determination of organochloride pesticides by gas chromatography.     

Optimisation of alachlor solid-phase microextraction from water samples using experimental design

We have tested screening and response surface experimental designs to optimise the solid-phase microextraction (SPME) of the widely used herbicide alachlor. Extraction time and sample volume were the only statistically significant factors from those studied. In the final optimised conditions the procedure was applied to the SPME-HPLC analysis of alachlor in spiked water samples with excellent figures of merit.     

Determination of diphenylether herbicides in water samples by solid-phase microextraction coupled to liquid chromatography

Solid-phase microextraction (SPME) coupled to LC for the analysis of five diphenylether herbicides (aclonifen, bifenox, fluoroglycofen-ethyl, oxyfluorfen, and lactofen) is described. Various parameters of extraction of analytes onto the fiber (such as type of fiber, extraction time and temperature, pH, impact of salt and organic solute) and desorption from the fiber in the desorption chamber prior to separation (such as type and composition of desorption solvent, desorption mode, soaking time, and flush-out time) were studied and optimized. Four commercially available SPME fibers were studied. PDMS/divinylbenzene (PDMS/DVB, 60 microm) and carbowax/ templated resin (CW/TPR, 50 microm) fibers were selected due to better extraction efficiencies. Repeatability (RSD, < 7%), correlation coefficient (> 0.994), and detection limit (0.33-1.74 and 0.22-1.94 ng/mL, respectively, for PDMS/DVB and CW/TPR) were investigated. Relative recovery (81-104% for PDMS/DVB and 83-100% for CW/TPR fiber) values have also been calculated. The developed method was successfully applied to the analysis of river water and water collected from a vegetable garden.     

纳米SiO2膜新型萃取头固相微萃取测定蔬菜中5种农药残留量的研究

建立了以纳米SiO2膜为萃取头涂层的固相微萃取(SPME)-气相色谱(GC)联用测定蔬菜中5种农药残留 (p,p′-DDD, p,p′-DDE, o,p′-DDT, p,p′-DDT, 联苯菊酯)的新方法. 探讨并优化了萃取时间、萃取温度和转子转速等参数.     

Analysis of chloroacetanilide herbicides in water samples by solid-phase microextraction coupled with gas chromatography-mass spectrometry

A solid-phase microextraction (SPME) method has been developed for the determination of 3 chloroacetanilide herbicides in both fresh and seawater samples. The extracted sample was analyzed by gas chromatography with mass spectrometry detection (GC-MS), and parameters affecting SPME operation including fibre type, sample pH, sample temperature, mixing speed and extraction time have been evaluated and optimized. The amount of dissolved organic matter (DOM) and the salt content both affected SPME extraction efficiency, but the presence of other competitive extractants such as organochlorine pesticides (OCPs) in the matrix showed no insignificance interference. The limit of detection (LOD) for acetochlor, metolachlor and butachlor were 1.2, 1.6 and 2.7 ng L⁻¹, respectively. The recoveries for the herbicides ranged from 79 to 102%, and the linear dynamic range was from 10 to 1000 ng L⁻¹. The developed method has been used to monitor herbicides contaminations in coastal water samples collected around Laizhou bay and Jiaozhou bay in Shandong peninsula, China. The concentrations of acetochlor and metolachlor ranged from undetectable to 78.5 ng L⁻¹ and undetectable to 35.6 ng L⁻¹, respectively. Butachlor was not observed but in only one sample and the concentration is lower than the limit of quantification (LOQ). The concentrations of the three herbicides in this study are low compared to most of the other places reported.     

A critical review of vacuum-assisted headspace solid-phase microextraction for environmental analysis

Vacuum-assisted headspace solid-phase microextraction (Vac-HSSPME) is an emerging analytical technique, which further advances HSSPME by providing lower detection limits of analytes with poor volatility at shorter extraction times. This review discusses the theoretical aspects and possibilities of the Vac-HSSPME technique for analysis of environmental samples. Optimization of key parameters, currently available equipment and methods for quantification of organic pollutants in water and soil are considered. Key problems and limitations of the technique are discussed along with possible approaches for its future development. The technique has a well-developed theory, which could be used for modeling of the extraction process, faster method development, and optimization. Wider application of the technique is limited by the lack of automation, which, however, seems possible to develop and implement by manufacturers of commercial multi-purpose autosamplers for gas chromatography instruments. It has been shown that Vac-HSSPME allows decreasing cross-contamination of samples from the laboratory air, which is advantageous for identification and quantification of trace environmental pollutants. Simple equipment for the technique makes it possible to apply for on-site sample preparation and analysis of environmental samples.     

Analysis of triazolopyrimidine herbicides in soils using field-enhanced sample injection-coelectroosmotic capillary electrophoresis combined with solid-phase extraction

In this work, a combined methodology using off-line solid-phase extraction (SPE), on-line field-enhanced sample injection (FESI) and coelectroosmotic capillary electrophoresis with UV detection (CE-UV) is developed for the trace analysis of five triazolopyrimidine sulfonanilide pesticides (i.e., flumetsulam, florasulam, cloransulam-methyl, diclosulam and metosulam). An adequate background electrolyte (BGE) was obtained for the separation of these pesticides using hexadimethrine bromide (HDB) as electroosmotic flow (EOF) modifier. This BGE consisted of 0.00042% HDB, 11 mM formic acid, 16 mM ammonium carbonate and 2.5 mM alpha-CD solution at pH 7.6. The use of this running buffer together with the FESI preconcentration method provided limits of detection (LODs) in the low microg/L range (i.e., between 13.0 and 31.5 microg/L). The optimized FESI-CE-UV method was combined with off-line SPE using C(18) cartridges and applied to the determination of the selected group of pesticides in soil samples. Recovery percentages ranged between 50 and 84% in these samples with LODs between 18 and 34 microg/kg. This work shows the great possibilities of the combined use of SPE-FESI-CE-UV to improve CE sensitivity allowing the achievement of LODs similar to other analytical techniques as GC or HPLC.     

Rapid analysis of environmental samples using solid-phase microextraction (SPME) and narrow bore capillary columns

The application of SPME, a solventless extraction procedure, is demonstrated for two environmental applications. Extraction of VOCs by SPME is coupled with analysis on short narrow bore capillary gas chromatography columns. The technique is shown both as a fast screening tool and as part of an analytical procedure when combined with a mass spectrometer. Data show the linear range of the procedure. The extraction of chlorinated pesticides from hazardous wastewater and drinking water by SPME is also described in this paper. SPME is compared to traditional extraction procedures with respect to cost, time, ease of use, solvent usage, and sample usage.     

Enrichment of nitrophenols from water by means of solid-phase microextraction

The fundamental suitability of solid-phase microextraction (SPME) has been investigated for the enrichment of partially well water-soluble and differently substituted polar nitrophenols. Two commercially available fibers coated with 100 m polydimethylsiloxane or 85 m polyacrylate, respectively, were compared with regard to the efficiency of the enrichment of these compounds. For all the compounds investigated, polyacrylate fiber showed a better affinity when the exposure time was longer in comparison with polydimethylsiloxane fiber. The salting-out and the enrichment at low pH-values increased the sensitivity of the process significantly.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthday     

Automated at-line solid-phase extraction-gas chromatographic analysis of micropollutants in water using the PrepStation

A fully automated at-line solid-phase extraction-gas chromatography procedure has been developed for the analysis of aqueous samples using the PrepStation. The sample extract is transferred from the sample preparation module to the gas chromatograph via an autosampler vial. With flame-ionization detection, limits of determination (S/N=10) of 0.05–0.13 μg/l were obtained for the analysis of HPLC-grade water when modifying the PrepStation by: (i) increasing the sample volume to 50 ml, (ii) increasing the injection volume up to 50 μl, and (iii) decreasing the desorption volume to 300 μl. The HP autosampler had to be modified to enable the automated “at-once” on-column injection of up to 50 μl of sample extract. The amount of packing material in the original cartridge had to be reduced to effect the decrease of the desorption volume. The total set-up did not require any further optimization after having set up the method once. The analytical characteristics of the organonitrogen and organophosphorus test analytes, i.e. recoveries (typically 75–105%), repeatability (2–8%) and linearity (0.09–3.0 μg/l) were satisfactory. The potential of the system was demonstrated by determining triazines and organophosphorus pesticides in river Rhine water at the 0.6 μg/l level using flame-ionization and mass-selective detection. No practical problems were observed during the analysis of more than 100 river water samples.     

Solid-phase microextraction coupled with high-performance liquid chromatography for the determination of phenylurea herbicides in aqueous samples

Solid-phase microextraction coupled with high-performance liquid chromatography was successfully applied to the analysis of nine phenylurea herbicides (metoxuron, monuron, chlorotoluron, isoproturon, monolinuron, metobromuron, buturon, linuron, and chlorbromuron). Polydimethylsiloxane-divinylbenzene (PDMS-DVB, 60 microm) and Carbowax-templated resin (CW-TPR, 50 microm) fibers were selected from four commercial fibers for further study because of their better extraction efficiencies. The parameters of the desorption procedure were studied and optimized. The effects of the properties of analytes and fiber coatings, carryover, duration and temperature of absorption, pH, organic solvent and ionic strength of samples were also investigated. External calibration with an aqueous standard can be used for the analysis of environmental samples (lake water) using either PDMS-DVB or CW-TPR fibers. Good precisions (1.0-5.9%) are achieved for this method, and the detection limits are at the level of 0.5-5.1 ng/ml.     

Applications of matrix solid-phase dispersion in food analysis

Matrix solid-phase dispersion (MSPD), a patented process for the simultaneous disruption and extraction of solid and semi-solid samples, was first reported in 1989. Since that time, MSPD has found application in numerous fields, but has proven to be particularly applicable for the analysis of drugs, pollutants, pesticides and other components in foods. The present article provides a review of these and related applications and discusses both the practical and theoretical aspects for the use of MSPD in sample processing.     

Determination of anatoxin-a in environmental water samples by solid-phase microextraction and gas chromatography-mass spectrometry

In the present work, a method was developed and optimized aiming at the determination of anatoxin-a in environmental water samples. The method is based on the direct derivatization of the analyte by adding hexylchloroformate in the alkalinized sample (pH = 9.0). The derivatized anatoxin-a was extracted by a solid-phase microextraction (SPME) procedure, submersing a PDMS fiber in an amber vial for 20 min under magnetic stirring. GC-MS was used to identify and quantify the analyte in the SIM mode. Norcocaine was used as internal standard. The following ions were chosen for SIM analyses (quantification ions in italics): anatoxin-a: 191, 164, 293 and norcocaine: 195, 136, 168. The calibration curve showed linearity in the range of 2.5-200 ng/mL and the LOD was 2 ng/mL. This method of SPME and GC-MS analysis can be readily utilized to monitor anatoxin-a for water quality control.     

Determination of phenylurea herbicides in natural waters at concentrations below 1 ng l using solid-phase extraction, derivatization, and solid-phase microextraction–gas chromatography–mass spectrometry

A procedure is presented which allows the ultratrace level determination of phenylurea herbicides (PUHs) in natural waters. Samples were enriched by solid-phase extraction (SPE) on Carbopack B and alkylated with iodoethane and sodium hydride to yield thermostable products. After derivatization, the aqueous samples were extracted and injected by SPME. The use of iodoethane instead of iodomethane allowed the differentiation between parent compounds and the N-demethylated metabolites. Limits of detection were between 0.3 and 1.0 ng/l for the parent compounds. Standard deviations below 10% were achieved for samples containing more than 4 ng/l in very different matrices including Nanopure water, lake water, and waste water treatment plant (WWTP) effluent. Moreover, the para-hydroxylated metabolite of diuron could be quantified with the same procedure. The presence of further metabolites was assessed qualitatively. Chromatography was stable over a large number of measurements even with dirty samples from WWTP effluent. The precision and sensitivity of the developed analytical method allowed the investigation of the fate of PUHs in lakes, their degradation during drinking water treatment and their transport within the North Sea.     

Determination of aldehydes in drinking water using pentafluorobenzylhydroxylamine derivatization and solid-phase microextraction

A headspace solid-phase microextraction (HS-SPME) procedure followed by gas chromatography and electron capture detection (GC-ECD) has been developed for the determination of aldehydes in drinking water samples at microg/l concentrations. A previous derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was performed due to the high polarity and instability of these ozonation by-products. Several SPME coatings were tested and the divinylbenzene-polydimethylsiloxane (DVB-PDMS) coating in being the most suitable for the determination of these analytes. Experimental SPME parameters such as selection of coating, sample volume, addition of salt, extraction time and temperature of desorption were studied. Analytical parameters such as precision, linearity and detection limits were also determined. HS-SPME was compared to liquid-liquid microextraction (proposed in US Environmental Protection Agency Method 556) by analyzing spiked water samples; a good agreement between results obtained with both techniques was observed. Finally, aldehydes formed at the Barcelona water treatment plant (N.E. Spain) were determined at levels of 0.1-0.5 microg/l. As a conclusion, HS-SPME is a powerful tool for determining ozonation by-products in treated water.     

Pesticide analysis in herbal infusions by solid-phase microextraction and gas chromatography with atomic emission detection

A direct immersion solid-phase microextraction (SPME) procedure was used in combination with capillary gas chromatography with atomic emission detection (GC-AED) for the determination of 10 pesticides (organochlorines, organophosphorus compounds and pyrethrins) in herbal and tea infusions. Ionic strength, sample dilution and time and temperature of the absorption and desorption stages were some of the parameters investigated in order to select the optimum conditions for SPME with a 100 μm PDMS fiber-coating. Element-specific detection and quantification was carried out by monitoring the chlorine (479 nm) and bromine (478 nm) emission lines, which provided nearly specific chromatograms. Calibration was carried out by using a spiked sample infusion. The detection limits varied between 11.9 ng ml⁻¹ for deltamethrin and 0.03 ng ml⁻¹ for p,p′-DDE and p,p′-DDD. The recoveries ranged from 73.5% for deltamethrin to 108.3% for p,p′-DDT in a spiked white tea infusion. Two of the eight samples analyzed contained low levels of some the pesticides considered.