Matrix solid-phase dispersion followed by gas chromatography tandem mass spectrometry for the determination of benzotriazole UV absorbers in sediments

A cost-effective and low solvent consumption method, based on the matrix solid-phase dispersion (MSPD) technique, for the determination of six benzotriazole UV absorbers in sediments is presented. Sieved samples (0.5 g) were first mixed in a mortar with a solid sorbent and then transferred to a polypropylene syringe containing a layer of clean-up co-sorbent. Analytes were eluted with a suitable solvent and further determined by gas chromatography with tandem mass spectrometry (GC-MS/MS). Under final conditions, diatomaceous earth and silica, deactivated to 10%, were used as inert dispersant and clean-up co-sorbent, respectively. Analytes were recovered using just 5 mL of dichloromethane, and this extract was concentrated and exchanged to 1 mL of isooctane. Further removal of co-extracted sulphur was achieved adding activated copper powder to final extracts, which were stored overnight, before injection in the GC-MS/MS system. The accuracy of the method was assessed with river and marine sediment samples showing different carbon contents and spiked at different concentrations in the range from 40 to 500 ng g⁻¹. Recoveries varied between 78% and 110% with associated standard deviations below 14%. The limits of quantification of the method stayed between 3 and 15 ng g⁻¹. Levels of target compounds in sediment samples ranged from not detected up to a maximum of 56 ng g⁻¹ for Tinuvin 328.     

Rapid determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin in water samples by using solid-phase microextraction followed by gas chromatography with tandem mass spectrometry

A rapid and simple method of using solid-phase microextraction was developed for determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) in water samples. In this method, the target analyte is extracted from the sample into the polymeric coating of the fused-silica fiber. After exposure, the fiber is thermally desorbed in the heated injection port of the gas chromatograph, and a chromatographic analysis is performed by using low-resolution tandem mass spectrometry. Parameters that may affect the extension of the microextraction process, such as sampling mode, sample volume, temperature, agitation, and sampling time, were studied. Extraction efficiencies for 3 coating fibers were investigated: 100 microm poly(dimethylsiloxane) (PDMS), 65 microm PDMS-divinylbenzene, and 75 microm carboxen-PDMS. Linearity was evaluated (R = 0.999) for a 250-fold concentration range from the fg/mL to the pg/mL level. The 2,3,7,8-TCDD was detected at the fg/mL level when the headspace over the water sample was sampled for 60 min; the limit of detection obtained was better than that of Method 8280B of the U.S. Environmental Protection Agency. The proposed method performed well when applied to the analysis of tap water, lake water, and seawater samples.     

Headspace solid-phase microextraction gas chromatography tandem mass spectrometry for the determination of brominated flame retardants in environmental solid samples

A headspace solid-phase microextraction gas chromatography coupled with tandem mass spectrometry (HSSPME-GC-MS-MS) methodology for determination of brominated flame retardants in sediment and soil samples is presented. To the best of our knowledge, this is the first time that SPME has been applied to analyze polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in environmental solid samples. Analyses were performed using 0.5-g solid samples moisturized with 2 mL water, employing a polydimethylsiloxane (PDMS) fiber coating, exposed to the headspace at 100 °C for 60 min. Several types of environmental solid samples were included in this study and the extraction efficiency was related to the organic matter content of the sample. Calibration was performed using real samples, and the method showed good linearity over a wide concentration range, precision, and afforded quantitative recoveries. The obtained detection limits were in the sub-ng g⁻¹ for all the target analytes in both samples. The proposed procedure was applied to several marine and river sediments and soils, some of which were found to contain PBDEs at concentrations in the ng g⁻¹ level; BDE-47, BDE-100, and BDE-99 were the major congeners detected. The proposed method constitutes a rapid and low-cost alternative for the analysis of the target brominated flame retardants in environmental solid samples, since the clean-up steps, fractionation, and preconcentration of extracts inherent to the classical multi-step solvent extraction procedures are avoided.      

Pressurized solvent extraction followed by gas chromatography tandem mass spectrometry for the determination of benzotriazole light stabilizers in indoor dust

A novel and sensitive method for the determination of five benzotriazole compounds (commonly used as light stabilizers) in indoor dust is presented. Pressurized liquid extraction (PLE) and gas chromatography followed by tandem in time mass spectrometry (GC–MS/MS) were used as sample preparation and determination techniques, respectively. Extraction and clean-up were integrated on-line and, after an evaporative concentration step, the extract provided by the PLE instrument was injected directly in the GC–MS/MS system. Parameters affecting the performance of the sample preparation process were evaluated using experimental factorial designs. Under optimized conditions, analytes were recovered from 0.5 g samples in 3 static extraction cycles of 10 min, using a hexane:dichloromethane (7:3) mixture, at 90 °C. Silica (1 g) was placed in the bottom of the extraction cells as clean-up sorbent. The recoveries of the method varied from 82 to 122%, with standard deviations below 13. The inter-day precision ranged from 9 to 12%, and the limits of quantification (LOQs) remained below 10 ng g⁻¹ for all species. For the first time, four of the five investigated species were found in dust from indoor environments. Their mean concentrations ranged from 71 to 780 ng g⁻¹.     

Sensitive determination of salicylate and benzophenone type UV filters in water samples using solid-phase microextraction, derivatization and gas chromatography tandem mass spectrometry

A sensitive procedure for the determination of three UV filters: ethylhexyl salicylate (EHS), 3,3,5-trimethylcyclohexyl salicylate (Homosalate, HMS), 2-hydroxy-4-methoxybenzophenone (BP-3) and two related hydroxylated benzophenones (2,4-dihydroxybenzophenone, BP-1 and 2,2′-dihydroxy-4-methoxybenzophenone, BP-8) in water samples is presented. Analytes were first concentrated on the coating of a solid-phase microextraction (SPME) fibre, on-fibre silylated and then determined using gas chromatography combined with tandem mass spectrometry (GC-MS/MS). Factors affecting the performance of extraction and derivatization steps are thoroughly evaluated and their effects on the yield of the sample preparation discussed. Under final working conditions, a PDMS-DVB coated SPME fibre was exposed directly to 10 mL of water, adjusted at pH 3, for 30 min. After that, the fibre was placed in the headspace (HS) of a 1.5 mL vial containing 20 μL of N-methyl-N-(trimethylsilyl)-trifluoroacetamide (MSTFA). On-fibre silylation of hydroxyl groups contained in the structure of target compounds was performed at 45 °C for 10 min. The whole sample preparation process was completed in 40 min, providing limits of quantification from 0.5 to 10 ng L⁻¹ and acceptable precision (RSDs under 13%) for samples spiked at different concentrations. All compounds could be accurately determined in river and treated wastewater (relative recoveries from 89 to 115%) using standards in ultrapure water, whereas standard addition is recommended to quantify their levels in untreated wastewater. Analysis of wastewater revealed the systematic presence of BP-3 and BP-1 in raw samples with maximum concentrations close to 500 and 250 ng L⁻¹, respectively.     

On-line solid-phase extraction coupled to ultra-performance liquid chromatography with tandem mass spectrometry detection for the determination of benzotriazole UV stabilizers in coastal marine and wastewater samples

Benzotriazoles are a group of UV absorbing compounds considered emerging contaminants that are used in different personal care products, and therefore, it is of high interest to develop sensitive and fast methods for investigating their presence in the environment. In this work, we present the development and application of a novel method based on on-line solid-phase extraction coupled to ultra-performance liquid chromatography with tandem mass spectrometry detection (SPE-UPLC-MS/MS) for the determination of seven benzotriazole UV stabilizers (BUVSs) in coastal marine and wastewater samples. This process is compared with a conventional off-line SPE procedure followed by UPLC-MS/MS. The parameters affecting the performance of the sample preparation and determination processes were evaluated. The results indicate that the on-line procedure provides for better sensitivity and reproducibility and is faster and easier than the off-line procedure. The detection limits and quantification limits achieved were in the range of 0.6–4.1 ng∙L⁻¹ and 2.1–14 ng∙L⁻¹ and relative standard deviation between 6.2 and 10 %. The developed method was applied to coastal marine and wastewater samples from Gran Canaria Island (Spain). All of the BUVSs studied were detected in the samples from wastewater treatment plants and two were found in the seawater samples (UV P in the range of 2.8–4.4 ng∙L⁻¹ and UV 360 between 3.6 and 5.2 ng∙L⁻¹).     

Applicability of solid-phase microextraction followed by on-fiber silylation for the determination of estrogens in water samples by gas chromatography-tandem mass spectrometry

A solvent-free method for the determination of five estrogens in water samples at the low ng/l was optimized. Compounds were first concentrated on a polyacrylate (PA) solid-phase microextraction (SPME) fiber, directly exposed to the water sample, and then on-fiber silylated on the headspace of a vial containing 50 microl of N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA). Derivatized analytes were determined using GC with MS/MS detection. Influence of several factors on the efficiency of the microextraction step (e.g. time, sample volume, pH, ionic strength and fiber coating) is systematically described. Derivatization conditions were optimized in order to achieve the complete silylation of all hydroxyl groups contained in the structure of the compounds. Detection limits (from 0.2 to 3 ng/l) are compared with those obtained using the same detection technique and different sample preparation strategies, such as solid-phase extraction followed by silylation of the analytes in the organic extract and SPME without derivatization. The method was applied to the analysis of sewage water samples. Two of the investigated species were detected above the quantification limits of the procedure.     

Headspace single drop microextraction of methylcyclopentadienyl-manganese tricarbonyl from water samples followed by gas chromatography-mass spectrometry

Headspace single drop microextraction coupled to gas chromatography-mass spectrometry yielded a simple, fast and virtually solventless analytical protocol used for the headspace analysis of aqueous samples contaminated with methylcyclopentadienyl-manganese tricarbonyl (MMT). Initially, several experimental parameters were controlled and optimized and the optimum conditions found were 2.5 μl octane microdrop exposed for 20 min to the headspace of a 10 ml aqueous sample (15 ml vial) containing 20% (w/v) NaCl and stirred at 1250 rpm. The calculated calibration curves gave a high level of linearity for MMT with correlation coefficients >0.9995 after conducting a 3-day study. The limit of detection was calculated to be 0.21 μg l⁻¹. The proposed method achieved an enrichment factor of the order of 2100 and a 53% recovery after extracting the spiked aqueous solution for 20 min under the optimized experimental conditions. The repeatability and intra-day reproducibility of the proposed method, expressed as relative standard deviation were 8.4 and 6.4%, respectively. Finally, analysis of spiked tap and wastewater samples revealed that matrix had little effect upon extraction.     

Determination of frequently detected herbicides in water by solid-phase microextraction and gas chromatography coupled to ion-trap tandem mass spectrometry

A method based on solid-phase microextraction (SPME) coupled with GC and ion trap tandem mass spectrometry has been developed for the analysis of nine herbicides and degradation products, among the most frequently found in natural water. A polydimethylsiloxane–divinylbenzene (PDMS–DVB)-coated fiber was selected to extract the analytes directly from the samples over the 0.01–1 μg L⁻¹ concentration range. Optimization of manual and automated SPME was performed on the basis of desorbed amounts, via various factorial experiment designs. Of the two modes, the automated one was found to be the most efficient. Memory effect was avoided owing to the 10-min fiber desorption time. Limits of detection reached down to below 0.01 μg L⁻¹ and repeatability ranged from 3 to 15% in natural water. A validation study was conducted involving the quantitation of the target compounds in Seine water with SPME/GC–MS-MS external calibration.     

Headspace solid-phase microextraction of oil matrices heated at high temperature and phthalate esters determination by gas chromatography multistage mass spectrometry

A solvent-free analytical approach based on headspace solid-phase microextraction (SPME) of oil matrices heated at high temperatures coupled to gas chromatography with mass spectrometry detector (GC-ion trap) has been developed for the determination of phthalic acid esters (PAEs) in oil matrices without sample manipulation. For this study, three fibers, i.e., 85 μm-polyacrylate (PA), 50/30 μm-divinylbenzene-carboxen-polydimethylsiloxane (DVB/CAR/PDMS) and 100 μm-polydimethylsiloxane (PDMS) were tested. Variables affecting the SPME headspace composition such as incubation sample temperature, sample incubation time and fiber exposition time were optimized. The optimal values found were 250 °C for sample incubation temperature and 30 min for incubation and extraction time. PA fiber was not suitable for the lightest polar phthalates which showed poor extraction and repeatability values. PDMS fiber had very poor response for some of the heavier and non-polar phthalates, whereas DVB/CAR/PDMS fiber showed the best response and repeatability values for the majority of the phthalates studied. The main benefit of the analytical method proposed is the absence of sample manipulation and hence avoidance of possible contamination coming from glassware, environment, solvents and samples.     

Development of a sensitive determination method for benzotriazole UV stabilizers in enviromental water samples with stir bar sorption extraction and liquid desorption prior to ultra‐high performance liquid chromatography with tandem mass spectrometry

Benzotriazole UV stabilizers are emerging compounds used in personal care products and can enter surface water after passing through wastewater treatment plants without being removed. Because these analytes are strongly hydrophobic, there is an environmental risk of accumulation in solid matrices and magnification through the trophic chain. In this work, a method based on stir bar sorption extraction with liquid desorption is presented for the extraction of benzotriazole UV stabilizers from water samples. Stir bar sorptive extraction was combined with ultra‐high performance LC with MS/MS detection. All important factors affecting the stir bar sorptive extraction procedure are discussed, and the optimized method was applied to seawater and wastewater samples from Gran Canaria Island, providing good selectivity and sensitivity with LODs and limits of quantification in the range of 18.4–55.1 and 61.5–184 ng/L, respectively. Recoveries between 68.4–92.2% were achieved for the more polar compounds, whereas the recoveries were lower for the two less polar compounds, most likely due to their strong absorption into the polydimethylsiloxane stir bar phase that does not allows the complete desorption. The repeatability studies gave RSDs of between 6.45 and 12.6% for all compounds in the real samples.     

Ultrasound-assisted leaching-dispersive solid-phase extraction followed by liquid-liquid microextraction for the determination of polybrominated diphenyl ethers in sediment samples by gas chromatography-tandem mass spectrometry

Ultrasound-assisted leaching-dispersive solid-phase extraction followed by dispersive liquid-liquid microextraction (USAL-DSPE-DLLME) technique has been developed as a new analytical approach for extracting, cleaning up and preconcentrating polybrominated diphenyl ethers (PBDEs) from sediment samples prior gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis. In the first place, PBDEs were leached from sediment samples by using acetone. This extract was cleaned-up by DSPE using activated silica gel as sorbent material. After clean-up, PBDEs were preconcentrated by using DLLME technique. Thus, 1 mL acetone extract (disperser solvent) and 60 μL carbon tetrachloride (extraction solvent) were added to 5 mL ultrapure water and a DLLME technique was applied. Several variables that govern the proposed technique were studied and optimized. Under optimum conditions, the method detection limits (MDLs) of PBDEs calculated as three times the signal-to-noise ratio (S/N) were within the range 0.02-0.06 ng g⁻¹. The relative standard deviations (RSDs) for five replicates were <9.8%. The calibration graphs were linear within the concentration range of 0.07-1000 ng g⁻¹ for BDE-47, 0.09-1000 ng g⁻¹ for BDE-100, 0.10-1000 ng g⁻¹ for BDE-99 and 0.19-1000 ng g⁻¹ for BDE-153 and the coefficients of estimation were ≥0.9991. Validation of the methodology was carried out by standard addition method at two concentration levels (0.25 and 1 ng g⁻¹) and by comparing with a reference Soxhlet technique. Recovery values were ≥80%, which showed a satisfactory robustness of the analytical methodology for determination of low PBDEs concentration in sediment samples.     

Headspace solid-phase microextraction combined with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry for the determination of volatile compounds from marine salt

In this work, a methodology to characterise the volatile and semi-volatile compounds from marine salt by headspace solid-phase microextraction (HS-SPME) and comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC/TOFMS) was developed. Samples from two saltpans of Aveiro, in Portugal, with diverse locations, obtained over three years (2004, 2005, and 2007) were analysed. A 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane SPME fibre was used. The volatiles present in the headspace of the solid salt samples (crystals) were equilibrated overnight at 60 °C and extracted for 60 min prior to injection in the GC × GC/TOFMS. 157 compounds, distributed over the chemical groups of hydrocarbons, aldehydes, esters, furans, haloalkanes, ketones, ethers, alcohols, terpenoids, C₁₃ norisoprenoids, and lactones were detected across the samples. Furans, haloalkanes and ethers were identified for the first time in marine salt. The large number of co-elutions on the first column that were resolved by the GC × GC system revealed the complexity of marine salt volatile composition. The existence of a structured 2D chromatographic behaviour according to volatility, in the first dimension (¹D), and primarily polarity, in the second dimension (²D), was demonstrated, allowing more reliable identifications. The resolution and sensitivity of GC × GC/TOFMS enabled the separation and identification of a higher number of volatile compounds compared to GC–qMS, allowing a deeper characterisation of this natural product.     

Rapid determination of amino acids in neonatal blood samples based on derivatization with isobutyl chloroformate followed by solid-phase microextraction and gas chromatography/mass spectrometry

The purpose of this study was to develop a simple, rapid and sensitive analytical method for determination of amino acids in neonatal blood samples. The developed method involves the employment of derivatization and a solid-phase microextraction (SPME) technique together with gas chromatography/mass spectrometry (GC/MS). Amino acids in blood samples were derivatized by a mixture of isobutyl chloroformate, methanol and pyridine, and the N(O,S)-alkoxycarbonyl alkyl esters thus formed were headspace extracted by a SPME fiber. Finally, the extracted analytes on the fiber were desorbed and detected by GC/MS in electron impact (EI) mode. L-Valine, L-leucine, L-isoleucine, L-phenylanaline and L-tyrosine in blood samples were quantitatively analyzed by measurement of the corresponding N(O,S)-alkoxycarbonyl alkyl esters using an external standard method. SPME conditions were optimized, and the method was validated. The method was applied to diagnosis of neonatal phenylkenuria (PKU) and maple syrup urine disease (MSUD) by the analyses of five amino acids in blood samples. The results showed that the proposed method is a potentially powerful tool for simultaneous screening for neonatal PKU and MSUD.     

Trace level determination of trichloroethylene in biological samples by headspace solid-phase microextraction gas chromatography/negative chemical ionization mass spectrometry

A gas chromatography/negative chemical ionization mass spectrometry (GC/NCIMS) method using headspace solid-phase microextraction (HS-SPME) was developed for the determination of trichloroethylene (TCE) in blood, liver, kidney, lung and brain. The method was optimized with respect to several parameters including extraction time, extraction temperature, desorption time and salt addition. The method showed good linearity over the range of 0.025-25 ng/mL in blood and 0.075-75 ng/g in tissues with correlation coefficient (R2) values higher than 0.99. The precision and accuracy for intra-day and inter-day measurements were less than 10%. The relative recoveries of all matrices were greater than 52%. Samples showed no significant loss during 8 h in the autosampler and following three freeze/thaw cycles. Validation results demonstrated that selected-ion monitoring of the 35Cl and 37Cl isotopes using NCI resulted in reliable and sensitive quantitation. This validated method was successfully applied to study the toxicokinetics of TCE following oral administration of extremely low doses of this potential human carcinogen to small test animals (rats).     

Application of solid-phase microextraction for the determination of organophosphorus pesticides in textiles by gas chromatography with mass spectrometry

A method based on solid-phase microextraction (SPME) and gas chromatography with mass spectrometry (GC/MS) for the determination of 18 organophosphorus pesticides (OPPs) in textiles is described. Commercially available SPME fibers, 100 μm PDMS and 85 μm PA, were compared and 85 μm PA exhibited better performance to the OPPs. Various parameters affecting SPME, including extraction and desorption time, extraction temperature, salinity and pH, were studied. The optimized conditions were: 35 min extraction at 25 °C, 5% NaSO₄ content, pH 7.0, and 3.5 min desorption in GC injector port at 250 °C. The linear ranges of the SPME-GC/MS method were 0.1-500 μg L⁻¹ for most of the OPPs. The limits of detection (LODs) ranged from 0.01 μg L⁻¹ (for bromophos-ethyl) to 55 μg L⁻¹ (for azinphos-methyl) and the RSDs were between 0.66% and 9.22%. The optimized method was then used to analyze 18 OPPs in textile sample, and the determined recoveries were ranged from 76.7% to 126.8%. Moreover, the distribution coefficients of the OPPs between 85 μm PA fiber and simulative sweat solution (K_pa/s) were determined. The determined K_pa/s of the OPPs correlated well with their octanol-water partition coefficients (r = 0.764 and 0.678) and water solubility (r = −0.892 and −0.863).     

Microwave-assisted extraction followed by headspace solid-phase microextraction and gas chromatography with mass spectrometry detection (MAE-HSSPME-GC-MS/MS) for determination of polybrominated compounds in aquaculture samples

This paper describes the first validated method for the extraction, purification and determination of trace levels of a number of pollutants of growing concern, including polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs), in aquaculture feeds and products. The new procedure comprises microwave-assisted extraction (MAE; optimized, using a central composite experimental design, to 15 min at 85 °C in 14 mL of 1:1 hexane/dichloromethane), and concentration by headspace solid-phase microextraction (HSSPME), and separation/quantification by gas chromatography with mass spectrometry detection (GC-MS/MS). The method was validated on the reference materials IAEA-406 and WMF-01. Limits of detection for fourteen of the fifteen analytes considered range from 10 to 600 pg g⁻¹, and limits of quantification from 50 pg g⁻¹ to 1.9 ng g⁻¹. Linear ranges, accuracies and precisions are reported.     

Mixed-mode solid-phase extraction followed by acetylation and gas chromatography mass spectrometry for the reliable determination of trans-resveratrol in wine samples

This work presents an advantageous analytical procedure for the accurate determination of free trans-resveratrol in red and white wines. The proposed method involves solid-phase extraction (SPE), acetylation of the analyte in aqueous media and further determination by gas chromatography (GC) with mass spectrometry detection (MS). The use of a mixed-mode SPE sorbent provides an improvement in the selectivity of the extraction step; moreover, the presence of several intense ions in the electron impact mass spectra of its acetyl derivative guarantees the unambiguous identification of trans-resveratrol. Considering a sample intake of 10 mL, the method provides a limit of quantification (LOQ) of 0.8 ng mL⁻¹ and linear responses for concentrations up to 2.5 μg mL⁻¹, referred to wine samples. The average recovery, estimated with samples fortified at different concentrations in the above range, was 99.6% and the inter-day precision stayed below 8%. Trans-resveratrol levels in the analyzed wines varied from 3.4 to 1810 ng mL⁻¹. Cis-resveratrol was also found in all samples. In most cases, equal or higher responses were measured for this latter form than for the trans-isomer. The reduced form of resveratrol, dihydro-resveratrol, was systematically identified in red wines.     

Determination of pesticides in aqueous samples by solid-phase microextraction in-line coupled to gas chromatography—mass spectrometry

A multiresidue method was developed for the determination of nitrogen- and phosphorous-containing pesticides (amines, anilides, phosphorothioates, and triazines) by solid-phase microextraction (SPME) in-line coupled to gas chromatography—mass spectrometry (GC/MS). The 85-µm polyacrylate fiber was first dipped into the aqueous sample for a given time and then directly introduced into the heated injector of the gas chromatography—mass spectrometer, where the analytes are thermally desorbed. The method was evaluated with respect to the limit of detection, linearity, and precision. The limit of detection [selected ion monitoring (SIM) mode] depends on the compound and varies from 5 to 90 ng/L. The method is linear over at least 3 orders of magnitude with coefficients of correlation usually ≥0.996. In general, the coefficient of variation (precision) is <10%. The partitioning of the analyte between the aqueous phase and the polymeric phase depends on the hydrophobicity of the compound as expressed by the octanol—water partitioning coefficient P _ow. The addition of sodium chloride has a strong effect on the extraction efficiency. This effect increases with decreasing hydrophobicity (increasing polarity) of the compound. The triazines atrazine, simazine, and terbuthylazine were first identified and quantified in water samples from the effluent of sewage plants by SPME-gas chromatography—nitrogen—phosphorus detection (GC/NPD). For such a complex matrix GC/NPD is not sufficiently selective for an unambiguous identification at low levels (<1 ppb) of pesticides. Selectivity may be enhanced by using SMPE-GC/MS in the SIM mode with three characteristic ions for each pesticide. This method allows an unequivocal identification and quantification at low levels of pesticides in environmental samples. At a target limit of detection below 100 ng/L, SPME-GC/MS represents a very simple, fast, selective, and solvent-free multimethod for the extraction and determination of these nitrogen- and phosphorous-containing pesticides from aqueous samples.     

Development of water-phase derivatization followed by solid-phase microextraction and gas chromatography/mass spectrometry for fast determination of valproic acid in human plasma

In this study, a simple, rapid, and sensitive method was developed and validated for the quantification of valproic acid (VPA), an antiepileptic drug, in human plasma, which was based on water-phase derivatization followed by headspace solid-phase microextraction (HS-SPME) and gas chromatography/mass spectrometry (GC/MS). In the proposed method, VPA in plasma was rapidly derivatized with a mixture of isobutyl chloroformate, ethanol and pyridine under mild conditions (room temperature, aqueous medium), and the VPA ethyl ester formed was headspace-extracted and simultaneously concentrated using the SPME technique. Finally, the analyte extracted on SPME fiber was analyzed by GC/MS. The experimental parameters and method validations were studied. The optimal conditions were obtained: PDMS fiber, stirring rate of 1100 rpm, sample temperature of 80 degrees C, extraction time of 20 min, NaCl concentration of 30%. The proposed method had a limit of quantification (0.3 microg/mL), good recovery (89-97%) and precision (RSD value less than 10%). Because the proposed method combined a rapid water-phase derivatization with a fast, simple and solvent-free sample extraction and concentration technique of SPME, the sample preparation time was less than 25 min. This much shortens the whole analysis time of VPA in plasma. The validated method has been successfully used to analyze VPA in human plasma samples for application in pharmacokinetic studies. All these results show that water-phase derivatization followed by HS-SPME and GC/MS is an alternative and powerful method for fast determination of VPA in biological fluids.