Reversed Electrode Polarity Stacking Mode Research Articles

Development of Two-Dimensional Offline Coupling of Asymmetrical Flow Field-Flow Fractionation and Capillary Electrophoresis for the Separation of a Five-Component Submicrometer Particle Mixture.

Submicrometer colloidal particles are widely applied in a variety of industrial products. While precise size and surface charge control is crucial to the stability and functionality of these materials, a tool to determine these properties with sufficient resolution, detection sensitivity, and robustness is still not available. The recently reported offline coupling of asymmetrical flow field-flow fractionation and capillary electrophoresis (AF4 × CE) shows success in improving the separation resolution for nanoparticles; however, challenges remain for sensitive multiple-component submicrometer particle analysis because of wide size and mobility distributions. We here report offline coupling of an AF4 method and a CE method, which utilized the online reversed electrode polarity stacking mode, to successfully characterize a five-component, submicrometer particle mixture. The mixture was successfully separated and detected with an improved inter- and intracomponent resolution. Therefore, our developed platform holds great potential for industrial applications involving multiple-component particle mixtures.

CE Coupled to ICP-MS and Single Particle ICP-MS for Nanoparticle Analysis.

Capillary electrophoresis (CE) can be used for the separation of nanoparticles (NPs). Coupling of CE to inductively coupled plasma mass spectrometry (ICP-MS) or single particle (sp)-ICP-MS enhances the analytical performance and capabilities of the method compared to CE with a standard detector (ultraviolet visible spectroscopy), in particular for trace analysis of metals or metal-containing compounds. spICP-MS is a method for NP analysis, where a standard ICP-MS setup is used with fast time-resolved detection in order to obtain information on individual NPs. Here we describe a method for the separation and detection of silver and gold NPs using CE-ICP-MS and CE-spICP-MS with reversed electrode polarity stacking mode (REPSM) for online preconcentration. CE-spICP-MS allows obtaining the average size, size distribution, elemental composition, and particle number concentration (PNC) of NPs in addition to a CE separation profile in a single run. Moreover, CE-spICP-MS can be used in some cases to separate NPs with different coatings.

Implementation of Online Preconcentration and Microsecond Time Resolution to Capillary Electrophoresis Single Particle Inductively Coupled Plasma Mass Spectrometry (CE-SP-ICP-MS) and Its Application in Silver Nanoparticle Analysis.

Capillary electrophoresis (CE) coupled to single particle inductively coupled plasma mass-spectrometry (SP-ICP-MS) was used for the first time with a prototype data acquisition (μsDAQ) system that features 5 μs time resolution (100% duty cycle) to separate and quantify mixtures of silver nanoparticles (Ag NPs). Additionally, an online preconcentration technique, reversed electrode polarity stacking mode (REPSM), was applied for Ag NPs analysis with CE-SP-ICP-MS for the first time. After optimization, best results were achieved using a injection time of 110 s and a constant pressure of 50 mbar in hydrodynamic injection mode. It was possible to detect 14.3 ± 1.5× more 20 nm sized, 21.0 ± 4.2× more 40 nm sized, and 27.7 ± 4.9× more 60 nm sized Ag NPs compared to the standard injection time of only 3 s. The effect of applied voltage on the NPs separation was studied, and a CE separation at 20 kV was found to be optimal for the present setup. The capability of CE-SP-ICP-MS for quantification of particle number concentration was investigated, and detection limits in the submicrogram-per-liter range were achieved. The possibility to separate 20, 40, and 60 nm sized Ag NPs simultaneously present in a mixture was demonstrated over a broad concentration range.

The in-capillary DPPH-capillary electrophoresis-the diode array detector combined with reversed-electrode polarity stacking mode for screening and quantifying major antioxidants in Cuscuta chinensis Lam.

An in-capillary 2, 2-diphenyl-1-picrylhydrazyl (DPPH)-CE-the DAD (in-capillary DPPH-CE-DAD) combined with reversed-electrode polarity stacking mode has been developed to screen and quantify the active antioxidant components of Cuscuta chinensis Lam. The operation parameters were optimized with regard to the pH and concentration of buffer solution, SDS, β-CDs, organic modifier, as well as separation voltage and temperature. Six antioxidants including chlorogenic acid, p-coumaric acid, rutin, hyperin, isoquercitrin, and astragalin were screened and the total antioxidant activity of the complex matrix was successfully evaluated based on the decreased peak area of DPPH by the established DPPH-CE-DAD method. Sensitivity was enhanced under reversed-electrode polarity stacking mode and 10- to 31-fold of magnitude improvement in detection sensitivity for each analyte was attained. The results demonstrated that the newly established in-capillary DPPH-CE-DAD method combined with reversed-electrode polarity stacking mode could integrate sample concentration, the oxidizing reaction, separation, and detection into one capillary to fully automate the system. It was considered a suitable technique for the separation, screening, and determination of trace antioxidants in natural products.

Fast and sensitive method to determine parabens by capillary electrophoresis using automatic reverse electrode polarity stacking mode: application to hair samples.

This paper describes a fast and sensitive method for the determination of methyl, ethyl, propyl, and butylparaben in hair samples by capillary electrophoresis using automatic reverse electrode polarity stacking mode. In the proposed method, solutions are injected using the flush command of the analysis software (940mbar) and the polarity switching is carried out automatically immediately after the sample injection. The advantages compared with conventional stacking methods are the increased analytical frequency, repeatability, and inter-day precision. All analyses were performed in a fused silica capillary (50cm, 41.5cm in effective length, 50μm i.d.), and the background electrolyte was composed of 20mmolL(-1) sodium tetraborate in 10% of methanol, pH 9.3. For the reverse polarity, -25kV/35s was applied followed by application of +30kV for the electrophoretic run. Temperature was set at 20°C, and all analytes were monitored at 297nm. The method showed acceptable linearity (r (2) > 0.997) in the studied range of 0.1-5.0mgL(-1), limits of detection below 0.017mgL(-1), and inter-day, intra-day, and instrumental precision better than 6.2, 3.6, and 4.6%, respectively. Considering parabens is widely used as a preservative in many products and the reported possibility of damage to the hair and also to human health caused by these compounds, the proposed method was applied to evaluate the adsorption of parabens in hair samples. The results indicate that there is a greater adsorption of methylparaben compared to the other parabens tested and also dyed hairs had a greater adsorption capacity for parabens than natural hairs.

Sample Stacking and On-Line Derivatization for the Analysisof Ampicillin and Amoxicillin by Microemulsion Electrokinetic Chromatography

A novel method using microemulsion electrokinetic chromatography (MEEKC) combining the preconcentration technique called reversed electrode polarity stacking mode (REPSM) with subsequent on-line derivatization has been developed for the quantitative determination of ampicillin and amoxicillin. It was found that the derivatization of antibiotics with 2,3-naphtalenedicarboxaldehyde (NDA) is accelerated greatly in microemulsion media, compared to the standard derivatization procedure, no heating being required. Various parameters that affect the ratio of derivatization, such as temperature, mixing and reaction time, concentration of NDA solution, and plug length were investigated and optimized. The combination of RESPM technique with the following derivatization allows the detection limits of ampicillin and amoxicillin to be decreased by a factor of 300 or more. The potential of the developed method was demonstrated by the determination of these antibiotics in a biological sample through the analysis of urine.

Analysis of phthalate esters in plastic-packaging bags by on-line sample stacking-microemulsion electrokinetic chromatography

Two convenient, effective, and reproducible methods using microemulsion electrokinetic chromatography (MEEKC)-normal stacking mode (NSM) and reversed electrode polarity stacking mode (REPSM) were developed for the on-line sample stacking of phthalate esters (PAEs). REPSM coupled with MEEKC increased the sensitivity of 937.5 to 7,143 times for four PAEs compared to the conventional MEEKC. The separating conditions in the MEEKC method were studied, and many factors influencing the two sample stacking processes were investigated in detail. The optimum sample matrices for the two stacking methods were as follows: 30 mmol/L sodium cholate (SC) and 30.0 mmol/L borate (pH 8.5). Additionally, sample injections as large as 3.45 kPa x 40 s and 3.45 kPa x 90 s were applied for NSM-MEEKC and REPSM-MEEKC, respectively. The linear relationship and reproducibility were also examined. Under the optimum conditions, the detection limits (S/N = 3) of the PAEs were in the ranges of 0.021 - 0.33 mg/L and 0.7 - 4 microg/L for NSM-MEEKC and REPSM-MEEKC, respectively. The proposed REPSM-MEEKC has been successfully applied to determine PAEs in plastic-packaging bags, and the spiked recoveries were in the range of 89.1% - 105.6% with satisfactory results.

Micellar nanotubes dispersed electrokinetic chromatography for the simultaneous determination of antibiotics in bovine milk

A method to determine four antibiotics for veterinary use (ciprofloxacin, enrofloxacin, florfenicol, and chloramphenicol) of different families (fluoroquinolones and amphenicols) in bovine milk was developed. The determination of the analytes was carried out using micellar electrokinetic capillary chromatography (MEKC) with a common sodium borate-SDS buffer solution containing single-walled carbon nanotubes (SWCNTs). In this way, a great improvement in the electrophoretic resolution and the separation efficiency was achieved compared to MEKC. An online reverse electrode polarity-stacking mode (REPSM) was carried out to enhance sensitivity. This step was performed in only 2 min and it allowed a stacked percentage of 103. That means that all the amount of injected analytes is effectively stacked. When this stacking procedure was combined with an off-line preconcentration step, based on SPE, analytes could be detected in lower concentration than the established maximum residue limits (MRLs). The LODs for the four compounds were between 6.8 and 13.8 μg L(-1) and the RSD values were between 1.1% and 6.6%. The whole method was applied to spiked real samples with acceptable precision and satisfactory recoveries.

Determination of organophosphorus pesticides using dispersive liquid–liquid microextraction combined with reversed electrode polarity stacking mode—micellar electrokinetic chromatography

A rapid and sensitive method using two preconcentration techniques, dispersive liquid–liquid microextraction (DLLME) followed by reversed electrode polarity stacking mode (REPSM) was developed for the analysis of five organophosphorus pesticides (OPPs) by micellar electrokinetic chromatography (MEKC). Parameters that affect the efficiency of the extraction in DLLME and preconcentration by REPSM, such as the kind and volume of the extraction and disperser solvents, salt addition, sample matrix and injection time were investigated and optimized. Under the optimum conditions, the enrichment factors were obtained in the range from 477 to 635. The linearity of the method for parathion, azinphos and fenitrithion was in the range of 20–1000ngmL−1, and for malathion and diazinon in the range of 50–1000ngmL−1, with correlation coefficients (r2) ranging from 0.9931 to 0.9992. The limits of detecton (LODs) at a signal-to-noice ratio of 3 ranged from 3 to 15ngmL−1. The relative recoveries of five OPPs from water samples at spiking levels of 20 and 200ngmL−1 for parathion, azinphos and fenitrithion, and 50 and 500ngmL−1 for malathion and diazinon, were 69.5–103%. The proposed method provided high enrichment factors, good precision and accuracy with a short analysis time.

Field enhancement sample stacking for analysis of organic acids in traditional Chinese medicine by capillary electrophoresis

A technique known as field enhancement sample stacking (FESS) and capillary electrophoresis (CE) separation has been developed to analyze and detect organic acids in the three traditional Chinese medicines (such as Portulaca oleracea L., Crataegus pinnatifida and Aloe vera L.). In FESS, a reverse electrode polarity-stacking mode (REPSM) was applied as on-line preconcentration strategy. Under the optimized condition, the baseline separation of eight organic acids (linolenic acid, lauric acid, p-coumaric acid, ascorbic acid, benzoic acid, caffeic acid, succinic acid and fumaric acid) could be achieved within 20min. Validation parameters of this method (such as detection limits, linearity and precision) were also evaluated. The detection limits ranged from 0.4 to 60ng/mL. The results indicated that the proposed method was effective for the separation of mixtures of organic acids. Satisfactory recoveries were also obtained in the analysis of these organic acids in the above traditional Chinese medicine samples.

Extremely highly efficient on-line concentration and separation of gold nanoparticles using the reversed electrode polarity stacking mode and surfactant-modified capillary electrophoresis

In this study, gold nanoparticles (Au NPs) were separated using the reversed electrode polarity stacking mode (REPSM) of a capillary electrophoresis (CE) system for on-line enhancement prior to performing surfactant-modified CE separation. Under optimized conditions [running electrolyte buffer, sodium dodecyl sulfate (70 mM) and 3-cyclohexylamino-1-propanesulfonic acid (10 mM) at pH 10.0; applied voltage, 20 kV; operating temperature, 25 °C; REPSM strategy for sample on-line concentration; REPSM applied prior to initializing separation], two parameters were varied to further enhance the concentration and separation of the Au NPs: (i) the rate of polarity switching (from −20 to +20 kV) between the REPSM and surfactant-modified CE separation modes and (ii) the length of the capillary column. At a polarity switching rate of 1333 kV min −1 and a column length of ca. 83.5 cm, the resolution of the separation of a mixture of 5.3- and 40.1-nm Au NPs was greater than 19; in addition, the numbers of theoretical plates for the 5.3- and 40.1-nm-diameter Au NPs were greater than 15,000 and up to 1.15 × 10 7, respectively—the latter being extremely high. Thus, this CE-based method for separating Au NPs provided high performance in terms of separation resolution and the number of theoretical plates, both of which were improved by greater than fivefold relative to those published previously. Notably, the sensitivity enhancement factors for the 5.3- and 40.1-nm-diameter Au NPs were improved (by ca. 20- and 500-fold, respectively) relative to those obtained using conventional surfactant-modified CE separation.

Reversed Electrode Polarity Stacking Sample Preconcentration Combined with Micellar Electrokinetic Chromatography for the Analysis of Carbamate Insecticide Residues in Fruit Juices

Reversed electrode polarity stacking mode (REPSM) coupled to micellar electrokinetic chromatography (MEKC) was employed for the simultaneous determination of carbamate insecticide residues in fruit juice samples. A mixture of the studied insecticides (i.e., methomyl, propoxur, carbofuran, carbaryl, isoprocarb, and promecarb) in 10 mmol L−1 phosphate buffer (pH 7.0) was introduced into the capillary tube by hydrodynamic injection at 0.5 psi for 30 s followed by removal of the sample matrix at −15 kV for 0.5 min. The analytes were successfully separated within 8 min using 10 mmol L−1 borate buffer containing 60 mmol L−1 sodium dodecyl sulfate at pH 9.5, and photodiode array detection at 205, 214, and 225 nm. The REPSM–MEKC gave stacking enhancement factors of about 4–13, compared to that without stacking. The limits of detection were in the range 0.01–0.10 mg L−1, which is acceptable with respect to the maximum residue limits. Good precisions were obtained with relative standard deviation lower than 1.8% (for migration time) and 10% (for peak area). The recoveries for most fruit juice samples were acceptable (>80%). No contamination of the studied carbamates was observed in any sample. The proposed method is simple and effective for preconcentration and removal of matrix interferences in a single step for the determination of the studied carbamate insecticides.

Monitoring the On-line Concentration and Separation of Gold Nanoparticles Using the Reversed Electrode Polarity Stacking Mode and Micellar Electrokinetic Chromatography

In this study, I separated gold nanoparticles (Au NPs) using the reversed electrode polarity stacking mode (REPSM) of a capillary electrophoresis system for on-line enhancement prior to performing micellar electrokinetic chromatography (MEKC). In the first part of this paper, I discuss the effects of several new and important parameters, the nature of the added salt, the pH of the sample matrix, and the size of the injection buffer plug that appears after introducing the samples, on the systems' on-line concentration and separation performance for a variety of sample compositions. In the second part of this paper, I describe my use of the optimized conditions to monitor the migration of the Au NPs during the concentration and separation processes. The results of these studies suggest that combining REPSM with MEKC is a very good strategy for the on-line concentration and separation of Au NPs at trace concentrations.

Determination of melamine and related triazine by-products ammeline, ammelide, and cyanuric acid by micellar electrokinetic chromatography

In this study, micellar electrokinetic chromatographic (MEKC) methods were developed for the detection of traces of melamine and its related by-products (ammeline, ammelide, and cyanuric acid). Two on-line sample concentration steps namely reversed electrode polarity stacking mode (REPSM) and cation-selective injection (CSI) were used for improving the detection sensitivity. For REPSM, a borate–NaOH buffer (pH 10, 35 mM) composed of 60 mM SDS and 10% (v/v) methanol, was used as carrier electrolyte, and samples were prepared in an aqueous solution of 10 mM NaOH. In CSI, a phosphate buffer (pH 2, 50 mM) containing 41 mM SDS was used as the carrier electrolyte, and samples were prepared with an aqueous solution of 10 mM NaOH and a phosphate buffer (pH 2.0, 25 mM) in a volume ratio of 1:9. The results indicated that REPSM enhanced all analyte signals except for melamine, which could be concentrated only by the CSI. The detection limit was reduced from 1.7 mg L −1 to 2.8 μg L −1 for melamine by the optimal CSI step, and from 0.23–1.2 mg L −1 to 2.4–5.0 μg L −1 for the other three analytes by the optimal REPSM step. Tableware made of melamine and samples of flour were used as test samples, and the results indicated that the proposed MEKC methods can successfully determine contaminations from melamine. The study also indicated that when the plastic made of melamine was exposed only once to an acidic solution (acetic or phosphoric acid) at 80 °C for 30 min, melamine continuously leached out from the test sample even without any further treatment with an acidic solution.

Using micellar electrokinetic chromatography for the highly efficient preconcentration and separation of gold nanoparticles

In this paper, we report the use of micellar electrokinetic chromatography (MEKC) for the highly efficient preconcentration and separation of gold nanoparticles (Au NPs). We used the reversed electrode polarity stacking mode (REPSM) of the MEKC system for the on-line enhancement and separation of the Au NPs. Several parameters had dramatic effects on the systems’ performance, including the concentration of sodium dodecylsulfate (SDS) surfactant, the presence of salts in the NP solution, the pH of the running electrolyte, and the temperature of the capillary. Under the optimized conditions [buffer: SDS (70 mM) and 3-cyclohexylamino-1-propanesulfonic acid (CAPS; 10 mM) at pH 10.0; applied voltage: 20 kV; operating temperature: 25 °C; additive: sodium dihydrogenphosphate (NaH 2PO 4, 10 mM); REPSM strategy for sample preconcentration], the number of theoretical plates for the 5.3- and 40.1-nm-diameter Au NPs were 3000 and (an ultrahigh) 2.1 × 10 6, respectively; in addition, the detection sensitivities toward the Au NPs were enhanced ca. 20- and 380-fold, respectively, relative to those obtained using standard MEKC analysis conditions. Furthermore, monitoring the electropherograms using diode-array detection allowed us to identify and characterize the sizes of the separated NPs from their UV–vis spectra. Our findings suggest that MEKC is a highly efficient tool for both the preconcentration and separation of NPs.

High‐sensitivity capillary electrophoresis for speciation of organomercury in biological samples using hollow fiber‐based liquid‐liquid‐liquid microextraction combined with on‐line preconcentration by large‐volume sample stacking

A hollow fiber-based liquid-liquid-liquid microextraction (HF-LLLME) combined with on-line large-volume sample stacking (LVSS) has been developed for the speciation of organomercury in biological samples by CE with UV detection. Separation was achieved in less than 11 min with an electrolyte consisting of 35 mM sodium tetraborate at pH 9.1. In LVSS, a reverse electrode polarity-stacking mode (REPSM) was applied as on-line preconcentration strategy. In HF-LLLME, the analytes were extracted from 12 mL volume of sample solution (pH adjusted to 3.0) into bromobenzene impregnated in the pores of the hollow fiber, and into an acceptor solution of L-cysteine (15 microL, 0.02% w/v) inside the hollow fiber. Under the optimized conditions, concentration factors of 2610-4580 were achieved and LODs in the range of 0.03-0.14 microg/L were feasible. The linearity was found to be over two orders of magnitude with correlation coefficient of 0.9991-0.9996. The developed method has been validated using a certified reference material (DORM-2, dogfish muscle), and the determined values coincided very well with the certified values. The method was also applied to the speciation of organomercury in three kinds of fish samples and human hair samples.

Solid-phase microextraction and sample stacking micellar electrokinetic chromatography for the analysis of pesticide residues in red wines

Solid-phase microextraction (SPME) in combination with sample stacking micellar electrokinetic chromatography (MEKC) was studied for the simultaneous determination of 11 multi-class pesticides residues (pirimicarb, metalaxyl, pyrimethanil, procymidone, nuarimol, azoxystrobin, tebufenozide, fenarimol, benalaxyl, penconazole and tetradifon) in red wines samples. Pesticide residues present in the samples were preconcentrated by SPME using poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fibers and the injection of large sample volumes into the capillary by reversed-electrode polarity stacking mode (REPSM). Validation of the method was carried out. The combination of both preconcentration procedures (SPME and REPSM) allowed the determination of 10 of these pesticides in red wines at concentrations between 0.049 and 1.69 mg/L ( i.e., levels well below the maximum residue limits (MRLs) allowed for these compounds in wine grapes, except for pirimicarb). Repeatability and accuracy of the SPME-MEKC-DAD method was verified by five consecutive extractions of spiked red wine samples at three levels of concentration. Apparent recovery values were in the range 90–107%. The potential of the method was demonstrated by analyzing multiple homemade red wine samples from the Canary Islands and two commercial samples. Only pyrimethanil, procymidone and azoxystrobin were found in the homemade samples; among them, the pesticide most frequently detected was procymidone.

Pesticide analysis in tomatoes by solid-phase microextraction and micellar electrokinetic chromatography

The analysis of a group of seven pesticides (i.e. six fungicides: pyrimethanil, procymidone, nuarimol, fenarimol, benalaxyl and penconazole and one insecticide: pirimicarb) in tomato samples by micellar electrokinetic chromatography is investigated. For this purpose, reversed electrode polarity stacking mode and solid-phase microextraction (SPME) have been used as on-line and off-line preconcentration procedures, respectively. Tomato samples were first homogenized and extracted with acetone. After suitable evaporation and reconstitution of the extract in water, a SPME procedure using poly(dimethylsiloxane)/divinylbenzene fibers was used. Due to the strong influence of the sample matrix in the extraction, a matrix matched calibration of spiked tomato samples was developed. The method was found to be linear between 0.5 and 2.5 mg/kg. Limits of detection achieved are below the maximum residue limits established by the European Union and Spain legislation as well as by the Codex Alimentarius (except for penconazole). The potential of the method was demonstrated by analyzing 12 tomato samples (of ecological and non-ecological production) taken from regional cultivars. No residues of the selected pesticides were detected in any of the samples.

Pesticide analysis in rose wines by micellar electrokinetic chromatography

In this work, the determination of 11 pesticides (pirimicarb, metalaxyl, pyrimethanil, procymidone, nuarimol, azoxystrobin, tebufenozide, fenarimol, benalaxyl, penconazole, and tetradifon) in rose wines by micellar EKC (MEKC) using reversed electrode polarity stacking mode (REPSM) as online preconcentration strategy is described. The MEKC buffer consisted of 100 mM sodium tetraborate and 30 mM SDS at pH 8.5 with 6% v/v 1-propanol. A solid-phase microextraction (SPME) procedure using PDMS/divinylbenzene (PDMS/DVB) fibers was applied to extract the selected pesticides from the rose wine samples. The comparison between the calibration curves obtained from hydroalcoholic solutions (12% v/v ethanol) and from rose wines (matrix matched calibration) showed the existence of a strong matrix effect. Furthermore, a comparison with calibration curves obtained with white wine samples also showed significant differences for most of the analyzed pesticides. As a result, a matrix matched calibration was developed. Quantitative extraction from spiked wine samples was carried out in triplicate at two levels of concentration (range 0.18-6.00 mg/L). LODs between 0.040 and 0.929 mg/L were achieved, which are below the maximum residue limits (MRLs) established for wine grapes (except for pirimicarb) by the EU and Spain legislation as well as by the Codex Alimentarius. The established method - which is solvent free, cost effective, and fast - was also applied to the analysis of several homemade rose wine samples and a commercial one. Two of the selected pesticides were found in some of the analyzed samples.

Multiple pesticide analysis in wine by MEKC combined with solid‐phase microextraction and sample stacking

In this work, a new method for the determination in white wines of 12 pesticides widely used in vine cultivars (namely, carbendazim, pirimicarb, metalaxyl, pyrimethanil, procymidone, nuarimol, azoxystrobin, tebufenozide, fenarimol, benalaxyl, penconazole, and tetradifon) using solid-phase microextraction (SPME) and MEKC with diode-array detection (DAD) was developed. The MEKC buffer consisted of 100 mM sodium tetraborate and 30 mM SDS at pH 8.5 with 6% v/v 1-propanol. Reversed-electrode polarity stacking mode (REPSM) was applied as on-line preconcentration strategy. In order to carry out an effective and sensitive determination of these pesticides in wine samples, an off-line SPME procedure was optimized by means of an experimental design. After studying the extraction performance of different SPME coatings, PDMS/divinylbenzene (PDMS/DVB) fibers were found the most appropriate for the extraction of most of these pesticides. Carbendazim and metalaxyl could not be extracted from wine samples. Calibration curves for extracted standards and fortified white wines were studied in order to determine the presence of a matrix effect. The combination of both preconcentration procedures (SPME and REPSM) allowed the determination of ten of these pesticides in white wines at concentrations between 0.054 and 0.113 mg/L. (i.e., levels well below the maximum residue limits (MRLs) allowed for these compounds in wine grapes). Ten homemade wines were they analyzed with the optimized method demonstrating the usefulness of the proposed procedure.