Determination of phenols in lake and ground water samples by stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry

A simple and inexpensive method for sorptive extraction of phenols from water samples is presented. A polydimethyl siloxane (PDMS) stir bar (Twister) is used as an extraction medium for derivatized phenols, which is thermally desorbed and analyzed by gas chromatography-mass spectrometry (GC-MS). Its performance was illustrated and evaluated for the enrichment of microg l(-1) to ng l(-1) of phenol and selected chlorophenols in water samples. The method showed good linearity, recoveries and blank levels, as well as advantages such as sensitivity, simplicity, low cost and high feasibility, being successfully applied for the analysis of phenolic compounds in natural water samples.     

A rapid method of diagnosing pulmonary tuberculosis using stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry

A fast method for detection of tuberculostearic acid (TBSA) in sputum samples is described. The samples, obtained from patients with known or suspected pulmonary tuberculosis, were decontaminated and concentrated before being analyzed by stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry (SBSE-TD-GC-MS). Prior to extraction, the mycobacterial lipids were hydrolyzed and then derivatized with ethyl chloroformate to increase the sorption of the compounds by the polydimethylsiloxane (PDMS) stir bar coating. The limit of detection (LOD) is 0.2 ng ml(-1). Four sputum samples that were classified by direct microscopy as smear-positive or negative were analyzed by GC-MS. TBSA was detected at concentrations ranging from 0.47 to 2.3 ng ml(-1). The method is sufficiently sensitive to detect TBSA directly in clinical samples without the need to culture the organisms.     

Analysis of 35 priority semivolatile compounds in water by stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry. I. Method optimisation

A multiresidue method for the determination of 35 organic micropollutants (pesticides and polycyclic aromatic hydrocarbons) in water has been optimised using stir bar sorptive extraction (SBSE) and thermal desorption coupled to capillary gas chromatography-mass spectrometry (GC-MS). In the present work, the different parameters affecting the extraction of the analytes from the water samples to the PDMS-coated stir bars and optimisation of conditions affecting thermal desorption are investigated. The optimised conditions consist of a 100-ml water sample with 20% NaCl addition extracted with 20 mm length x 0.5 mm film thickness stir bars at 900 rpm during 14 h at ambient temperature. Desorption is carried out at 280 degrees C during 6 min under a helium flow of 75 ml/min in the splitless mode while maintaining a cryofocusing temperature of 20 degrees C in the programmed-temperature vaporisation (PTV) injector of the GC-MS system. Finally, the PTV injector is ramped to a temperature of 280 degrees C and the analytes are separated in the GC and detected by MS using full scan mode (m/z 60-400). Under the described conditions, the good repeatability, high analyte recoveries and robustness, make SBSE a powerful tool for routine quality control analysis of the selected semivolatile compounds in water samples.     

Simultaneous determination of 64 pesticides in river water by stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry

A method for determining 68 pesticides in river water using stir bar sorptive extraction (SBSE)-thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS) is described. SBSE sampling was optimized for sample solution pH, salting-out and methanol addition. Although salting-out enhanced the ability of the method to extract most of the pesticides with low absolute recoveries, the absolute recoveries of four pesticides were not improved by salting-out. The detection limits of the method for the pesticides ranged from 0.2 to 20 ng/l. Analyte recoveries from a river water sample spiked with standards at 10 and 100 ng/l were 58.5–132.0% (RSD: 1.8–15.8%) and 61.0–121.3% (RSD: 1.4–20.2%), respectively.     

Fast screening of pesticide multiresidues in aqueous samples by dual stir bar sorptive extraction-thermal desorption-low thermal mass gas chromatography-mass spectrometry

A method for fast screening of pesticide multiresidues in aqueous samples using dual stir bar sorptive extraction-thermal desorption-low thermal mass gas chromatography-mass spectrometry (dual SBSE-TD-LTM-GC-MS) has been developed. Recovery of 82 pesticides - organochlorine, carbamate, organophosphorous, pyrethroid and others - for the SBSE was evaluated as a function of octanol-water distribution coefficients (logK(o/w): 1.7-8.35), sample volume (2-20mL), salt addition (0-30% NaCl), and methanol addition (0-20%). The optimized method consists of a dual SBSE performed simultaneously on respectively a 20-mL sample containing 30% NaCl and a 20-mL sample without modifier (100% sample solution). One extraction with 30% NaCl is mainly targeting solutes with low K(o/w) (logK(o/w)<3.5) and another extraction with unmodified sample solution is targeting solutes with medium and high K(o/w) (logK(o/w)>3.5). After extraction, the two stir bars are placed in a single glass desorption liner and are simultaneously desorbed. The desorbed compounds are analyzed by use of LTM-GC-MS with fast temperature programming (75 degrees Cmin(-1)) using a 0.18mm i.d. narrow-bore capillary column and fast scanning (10.83 scan s(-1)) using quadrupole MS. The method showed good linearity (r(2)>0.9900) and high sensitivity (limit of detection: <10ngL(-1)) for most of the target pesticides. The method was applied to the determination of pesticides at nanograms per liter levels in river water and brewed green tea.     

Mercury speciation and analysis in drinking water by stir bar sorptive extraction with in situ propyl derivatization and thermal desorption-gas chromatography-mass spectrometry

A method for mercury analysis and speciation in drinking water was developed, which involved stir bar sorptive extraction (SBSE) with in situ propyl derivatization and thermal desorption (TD)-GC-MS. Ten millilitre of tap water or bottled water was used. After a stir bar, pH adjustment agent and derivatization reagent were added, SBSE was performed. Then, the stir bar was subjected to TD-GC-MS. The detection limits were 0.01 ng mL(-1) (ethylmercury; EtHg), 0.02 ng mL(-1) (methylmercury; MeHg), and 0.2 ng mL(-1) (Hg(II) and diethylmercury (DiEtHg)). The method showed good linearity and correlation coefficients. The average recoveries of mercury species (n=5) in water samples spiked with 0.5, 2.0, and 6.0 ng mL(-1) mercury species were 93.1-131.1% (RSD<11.5%), 90.1-106.4% (RSD<7.8%), and 94.2-109.6% (RSD<8.8%), respectively. The method enables the precise determination of standards and can be applied to the determination of mercury species in water samples.     

Optimisation of stir bar sorptive extraction and in-tube derivatisation-thermal desorption-gas chromatography-mass spectrometry for the determination of several endocrine disruptor compounds in environmental water samples

The analysis of organic pollutants in environmental water samples requires a pre-concentration step. Pre-concentration techniques such as stir bar sorptive extraction (SBSE) have gained popularity since they minimise the use of toxic organic solvents and can be considered as green analytical techniques. Similar to other pre-concentration techniques, one of the problems when SBSE is used is the matrix effect, which often occurs during the analysis of environmental water samples such as estuarine or wastewater samples. The present work studied the matrix effect during SBSE coupled to in-tube derivatisation–thermal desorption (TD)–gas chromatography–mass spectrometry for the determination of several endocrine disruptor compounds, such as alkylphenols, bisphenol A, estrogens and sterols, in environmental water samples, after optimisation of the major variables affecting the determination. Variables such as the addition of methanol or an inert salt to the donor phase, the extraction temperature, the volume of the donor phase, the stirring rate and the extraction time were studied during the SBSE optimisation. In the case of the in-tube derivatisation and TD step, the volume of the derivatisation reagent (N,O-bis(trimethylsilyl)triufloroacetamide with 1% of trimethylchlorosilane (BSTFA + 1% TMCS)) and the cryo-focusing temperature were fixed (2 μL and −50 °C, respectively) according to a consensus between maximum signal and optimal operation conditions. Good apparent recovery values (78–124%) were obtained for most of the analytes in Milli-Q water, except for 4-tert-octylphenol (4-tOP), which showed apparent recovery values exceeding 100%. Precision (n = 4) was in the 2–27%, and method detection limits were in the low nanogrammes per litre level for most of the analytes studied. The matrix effect was studied using two different approaches. On the one hand, Milli-Q water samples were spiked with humic acids, and apparent recovery values were studied with and without correction with the corresponding deuterated analogue. On the other hand, estuarine water and wastewater samples were spiked with known concentrations of target analytes, and apparent recoveries were studied as explained above. In general, the matrix effect could be corrected with the use of deuterated analogues, except for 4-tOP and nonylphenols for which [²H₄]-n-nonylphenol did not provide good corrections.     

Development of a stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry method for determining synthetic musks in water samples

This study presents the development of an analytical method for determining 9 synthetic musks in water matrices. The developed method is based on stir bar sorptive extraction (SBSE), coated with polydimethylsiloxane, and coupled with a thermal desorption–gas chromatography–mass spectrometry system (TD–GC–MS). SBSE can efficiently trap and desorb the analytes providing low limits of detection (between 0.02 ng L⁻¹ and 0.3 ng L⁻¹). Method validation showed good linearity, repeatability and reproducibility for all compounds. Furthermore, the limited manipulation of the sample required in this method implies a significant decrease of the risk of external contamination of the samples. The performance of the method in real samples was evaluated by analysing biological wastewater treatment plant (WWTP) influent and effluent samples, reverse osmosis treatment plant effluents and river waters. The most abundant musk was galaxolide with values up to 2069 ng L⁻¹ and 1432 ng L⁻¹ in the influent and effluent of urban WWTP samples, respectively. Cashmeran, Pantolide and Tonalide were also detected in all the matrices with values up to 94 ng L⁻¹, 26 ng L⁻¹ and 88 ng L⁻¹, respectively. Although in Europe the use of nitromusks in cosmetics is prohibited, musk xylene and musk ketone were detected both in the WWTP and in the river samples. As far as we know, this is the first time than a SBSE method coupled with TD is applied for the determination of synthetic musks in water samples.     

Simultaneous analysis of benzophenone sunscreen compounds in water sample by stir bar sorptive extraction with in situ derivatization and thermal desorption-gas chromatography-mass spectrometry

A method for the simultaneous measurement of benzophenone (BP) sunscreen compounds, its derivatives 2,4-dihydroxybenzophenone (BP-1), 2-hydroxy-4-methoxybenzophenone (BP-3), 2-hydroxy-4-methoxy-4'-methylbenzophenone (BP-10), 2-hydroxybenzophenone (2OH-BP), 3-hydroxybenzophenone (3OH-BP) and 4-hydroxybenzophenone (4OH-BP), in water samples was developed using stir bar sorptive extraction (SBSE) with in situ derivatization followed by thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS). The detection limit is 0.5-2 ng L(-1) (ppt) for the seven BPs. The method shows good linearity and the correlation coefficients are equal to or higher than 0.990 for all the analyte. The average recoveries of BPs range from 102.0 to 128.1% (RSD<15.4%, n=6). Trace amounts of BPs in river water samples were determined by the present method.     

Simultaneous determination of alkylphenols and bisphenol A in river water by stir bar sorptive extraction with in situ acetylation and thermal desorption-gas chromatography-mass spectrometry

A method for the determination of seven alkylphenols and bisphenol A by stir bar sorptive extraction (SBSE) with in situ derivatization-thermal desorption (TD)-gas chromatography (GC)-mass spectrometry (MS) is described. SBSE was performed with in situ acetylation and without derivatization for comparison. For 4-tert-butylphenol and bisphenol A, in situ acetylation improved the responses in SBSE-TD-GC-MS. The method detection limits ranged from 0.1 to 3.2 ng/l. The recoveries of the analytes from a river water sample spiked with standards at 10 and 100 ng/l were 85.3-105.9% (R.S.D., 3.0-11.0%) and 88.3-105.8% (R.S.D., 1.6-8.3%), respectively.     

Stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry for trace analysis of triclosan in water sample

A simple and highly sensitive method called stir bar sorptive extraction (SBSE) and thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of 5-chloro-2-(2,4-dichlorophenoxy)phenol (triclosan) in river water samples, is described. A stir bar coated with polydimethylsiloxane (PDMS) is added to a 10mL water sample and stirring is carried out for 120min at room temperature (25 degrees C) in a vial. Then, the PDMS stir bar is subjected to TD-GC-MS. The detection limit of triclosan is 5ngL(-1) (ppt). The method shows linearity over the calibration range (0.02-20mugL(-1)) and the correlation coefficient is higher than 0.997 for triclosan standard solution. The recovery of triclosan in river water samples ranges from 91.9 to 108.3% (RSD: 4.0-7.0%). This simple, accurate, sensitive, and selective analytical method may be used in the determination of trace amounts of triclosan in river water samples.     

Determination of 4-nonylphenol and 4-tert.-octylphenol in water samples by stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry

A simple and highly sensitive method called thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of 4-nonylphenol (NP) and 4-tert.-octylphenol (OP) in water samples, is described. NP and OP in samples are extracted from water samples and concentrated by the stir bar sorptive extraction (SBSE) technique. A stir bar coated with polydimethylsiloxane (PDMS) is added to a 2.0 ml water sample and stirring is carried out for 60 min at room temperature (25 °C) in a headspace vial. Then the extract is high sensitively analyzed by TD-GC-MS without any derivatization step. The optimum SBSE conditions are realized at an extraction time of 60 min. The detection limits are 0.02 ng ml⁻¹ for NP and 0.002 ng ml⁻¹ for OP. The method shows good linearity over the concentration range of 0.1-10 ng ml⁻¹ for NP and 0.01-10 ng ml⁻¹ for OP, and the correlation coefficients are higher than 0.999. The average recoveries of NP and OP are higher than 97% (R.S.D.: 3.6-6.2%) with correction using the added surrogate standards, 4-(1-methyl) octylphenol-d₅ and deuterium 4-tert.-octylphenol. This simple, accurate, sensitive and selective analytical method may be used in the determination of trace amounts of NP and OP in tap and river water samples.     

Overall calibration procedure via a statistically based matrix-comprehensive approach in the stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry analysis of pesticide residues in fruit-based soft drinks

Stir bar sorptive extraction (SBSE)-thermal desorption (TD) procedure combined with gas chromatography mass spectrometry (GC-MS) and the statistical variance component model (VCM) is applied to the determination of semi-volatile compounds including organochlorine and organophosphorus pesticides in various synthetic and real fruit-based soft drink matrices. When the matrix effects are corrected using isotopically labelled or non labelled internal standard, but matrix/calibration run-induced deviations are still present in the measurements, the adoption of a variance component model (VCM) in the quantitative analysis of various matrices via an overall calibration curve is successful. The method produces an overall calibration straight line for any analyte accounting for the uncertainty due to all the sources of uncertainty, namely matrix-induced deviations, calibration runs performed at different times, measurement errors. Small increases in the detection limits and in uncertainty in the concentration values obtained in the inverse regression face favourably the decrease in times and costs for routine analyses.     

Simultaneous determination of parabens and synthetic musks in water by stir-bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry

This study focuses on a method for simultaneously determining personal care products in a wide range of polarities in different water matrices. The method is based on stir‐bar sorptive extraction followed by thermal desorption‐gas chromatography‐mass spectrometry. Prior to extraction, the parabens were acetylated to improve their affinity for the polydimethylsiloxane phase of the stir bar. The method showed good linearity, repeatability and reproducibility between days for all compounds and limits of detection at low ng/L levels (between 0.02 and 0.3 ng/L). The proposed method is also environmentally friendly, because it does not use organic solvents, and reduces the risk of external pollution, due to the minimal manipulation of the sample required. The method developed was successfully applied for the analysis of personal care products in different kinds of water matrices: influents and effluents of urban and industrial wastewater treatment plants, effluents of a reverse osmosis treatment plant and river waters. The influents of urban treatment plants generally showed the highest values for synthetic musks, with concentrations of up to 2219 ng/L of galaxolide, whereas the highest concentrations of parabens were detected in the industrial treatment plants influents.     

Multi-residue screening of pesticides in vegetables,fruits and baby food by stir bar sorptive extraction-thermal desorption-capillary gas chromatography-mass spectrometry

The performance of stir bar sorptive extraction (SBSE) for the enrichment of pesticides from vegetables, fruits and baby food samples is discussed. After extraction with methanol, an aliquot is diluted with water and SBSE is performed for 60 min. By applying a new thermal desorption unit (TDU), fully automated and unattended desorption of 98 stir bars is feasible, making SBSE very cost-effective. The presence of pesticide residues is elucidated with the retention time locked gas chromatography–mass spectroscopy method (RTL-capillary GC–MS). With SBSE–RTL-capillary GC–MS operated in the scan mode, more than 300 pesticides can be monitored in vegetables, fruits and baby food. The multi-residue method (MRM) described provides detectabilities from the mg/kg (ppm) to the sub-μg/kg (ppb) level, thereby complying with the maximum residue levels (MRLs) set by regulatory organizations for pesticides in different matrices. Several examples, i.e. pesticide residues in lettuce, pears, grapes and baby food, illustrate the potential of SBSE–RTL-capillary GC–MS.     

Multiresidue analysis of acidic and polar organic contaminants in water samples by stir-bar sorptive extraction-liquid desorption-gas chromatography-mass spectrometry

The feasibility of stir-bar sorptive extraction (SBSE) followed by liquid desorption in combination with large volume injection (LVI)-in port silylation and gas chromatography-mass spectrometry (GC-MS) for the simultaneous determination of a broad range of 46 acidic and polar organic pollutants in water samples has been evaluated. The target analytes included phenols (nitrophenols, chlorophenols, bromophenols and alkylphenols), acidic herbicides (phenoxy acids and dicamba) and several pharmaceuticals. Experimental variables affecting derivatisation yield and peak shape as a function of different experimental PTV parameters [initial injection time, pressure and temperature and the ratio solvent volume/N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) volume] were first optimised by an experimental design approach. Subsequently, SBSE conditions, such as pH, ionic strength, agitation speed and extraction time were investigated. After optimisation, the method failed only for the extraction of most polar phenols and some pharmaceuticals, being suitable for the determination of 37 (out of 46) pollutants, with detection limits for these analytes ranging between 1 and 800 ng/L and being lower than 25 ng/L in most cases. Finally, the developed method was validated and applied to the determination of target analytes in various aqueous environmental matrices, including ground, river and wastewater. Acceptable accuracy (70-130%) and precision values (<20%) were obtained for most analytes independently of the matrix, with the exception of some alkylphenols, where an isotopically labelled internal standard would be required in order to correct for matrix effects. Among the drawbacks of the method, carryover was identified as the main problem even though the Twisters were cleaned repeatedly.     

Stir bar sorptive extraction with in situ derivatization and thermal desorption-gas chromatography-mass spectrometry for determination of chlorophenols in water and body fluid samples

A new method, stir bar sorptive extraction (SBSE) with in situ derivatization and thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of chlorophenols, such as 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TrCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP), in tap water, river water and human urine samples, is described. The derivatization conditions with acetic acid anhydride and the SBSE conditions such as extraction time are investigated. Then, the stir bar is subjected to TD followed by GC-MS. The detection limits of the chlorophenols in tap water, river water and human urine samples are 1-2, 1-2, and 10-20 pg ml⁻¹ (ppt), respectively. The calibration curves for the chlorophenols are linear and have correlation coefficients higher than 0.99. The average recoveries of the chlorophenols in all the samples are higher than 95% (R.S.D. < 10%) with correction using added surrogate standards, 2,4-dichlorophenol-d₅, 2,4,6-trichlorophenol-¹³C₆, 2,3,4,6-tetrachlorophenol-¹³C₆ and pentachlorophenol-¹³C₆. This simple, accurate, sensitive and selective analytical method may be applicable to the determination of trace amounts of chlorophenols in liquid samples.     

Development of a method for the determination of UV filters in water samples using stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry

Stir bar sorptive extraction (SBSE) in combination with thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) was applied for the determination of 9 UV filters in water samples. The stir bar coated with polydimethylsiloxane (PDMS) was added to 20 mL of water sample at pH 2 (10% MeOH) and stirred at 1000 rpm for 180 min. Then, the stir bar was subjected to TD-GC-MS. The desorption conditions (desorption temperature and desorption time) and SBSE parameters (ionic strength, pH, presence of organic solvent and time) were optimised using a full factorial design and a Box-Behnken design, respectively. The method shows good linearity (correlation coefficients >0.994) and reproducibility (RSD<16%). The extraction efficiencies were above 63% for all the compounds. Detection limits were between 0.2 and 63 ng/L. The developed method offers the ability to detect several UV filters at ultra-low concentration levels with only 20 mL of sample volume. The effectiveness of the method was tested by analysing real samples such as lake water, river water and treated wastewater. The application of the method allowed reporting the levels of UV filters in environmental water samples.     

Simultaneous determination of unmodified sevoflurane and of its metabolite hexafluoroisopropanol in urine by headspace sorptive extraction-thermal desorption-capillary gas chromatography-mass spectrometry

Unmodified sevoflurane and its metabolite, hexafluoroisopropanol (HFIP), have both been proposed as biomarkers of exposure in post-shift urine for operating room personnel exposed to inhalation anaesthetic sevoflurane. We used headspace sorptive extraction (HSSE) and thermal desorption-capillary GC-MS to assess sensitively both compounds in the urine matrix (after a HFIP deconjugation step). In GC-MS splitless mode, calibration plots (approximately 15-650 microg/L) were linear (r2 > 0.9910) and the limits of detection (1 microg/L for both biomarkers) showed increased sensitivity for HFIP with respect to the previously described headspace GC-MS method. The method was suitable for biological monitoring of both biomarkers of exposure to sevoflurane.     

Determination of stale-flavor carbonyl compounds in beer by stir bar sorptive extraction with in-situ derivatization and thermal desorption-gas chromatography-mass spectrometry

A method for the determination of stale-flavor carbonyl compounds including E-2-octenal, E-2-nonenal, E,Z-2,6-nonadienal and E,E-2,4-decadienal in beer was developed using stir bar sorptive extraction (SBSE) with in-situ derivatization followed by thermal desorption-GC-MS analysis. The derivatization conditions with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine and the SBSE conditions--sampling mode, salt addition, sample volume, polydimethylsiloxane volume (sample/polydimethylsiloxane phase ratio) and extraction time--were examined. The method showed good linearity over the concentration range from 0.1 to 10 ng ml(-1) for all analytes and the correlation coefficients were higher than 0.9993. The limits of detection ranged from 0.021 to 0.032 ng ml(-1) for all analytes. The recoveries (98-101%) and precision (RSD 2.4-7.3%) of the method were examined by analyzing beer samples fortified at the 0.5-ng ml(-1) level. The method was successfully applied to low-level concentration samples.