Polydimethylsiloxane/divinylbenzene Research Articles

Analysis of aldehydes in water by solid-phase microextraction with on-fiber derivatization

The solid-phase microextraction (SPME) technique with on-fiber derivatization was evaluated for the analysis of aldehydes in water. The poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber was used and O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) were first loaded onto the fiber. The aldehydes in water sample were agitated into headspace and extracted by SPME with on-fiber derivatization. Gas chromatography/mass spectrometry (GC/MS) was used for the analysis of oximes formed and the adsorption-time profiles were examined. The precision, recovery and method detection limits (MDLs) were evaluated with spiked bidistilled water, chlorinated tap water as well as well water. The relative standard deviations from different spiked water sample were all less than 10% and the recoveries were 100±15%. With 2 ml of water sample, MDLs were in the range of 0.12–0.34 μg/l. Compared with other techniques, the study shown here provided a simple, fast and reliable method for the analysis of aldehydes in water.

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 μm) and Carbowax–templated resin (CW–TPR, 50 μm) 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.

Optimisation of a solid-phase microextraction procedure for the determination of triazines in water with gas chromatography–mass spectrometry detection

A procedure based on solid-phase microextraction (SPME) and gas chromatography–mass spectrometry, operating in the chemical ionisation mode, was developed and optimised in order to determine 10 triazines in water samples. Five different SPME fibers available for analysis [polydimethylsiloxane (PDMS) 100 μm, polyacrylate (PA) 80 μm, PDMS–divinylbenzene (DVB) 65 μm, Carbowax (CW)–DVB 65 μm, and Carboxen (CAR)–PDMS 75 μm] were tested, and PDMS–DVB was selected. To enhance the sensitivity of the SPME, variables affecting adsorption and desorption steps such as temperature, time, pH and ionic strength of the solution were optimised. Detection limits obtained were ranged between 2 and 17 ng l −1, and precision values were below 8% for the selected PDMS–DVB fiber. The optimised method was applied to real water samples and no triazines were detected.

Optimisation of headspace solid-phase microextraction for the analysis of volatile phenols in wine

Headspace solid-phase microextraction has been applied to the analysis of volatile phenols in wine. Silica fibre coated with Carbowax–divinylbenzene was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, polyacrylate, carboxen–polydimethylsiloxane, and polydimethylsiloxane–divinylbenzene. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength and sample volume were optimised using a two-level factorial design expanded further to a central composite design, in order to evaluate several possibly influential and/or interacting factors. The headspace (HS)-SPME procedure developed shows adequate detection and quantitation limits, and linear ranges for correctly analysing these compounds in wine. The recoveries obtained were close to 100%, with repeatability values lower than 16%. The method was applied to a variety of white and red wines.

Solid-phase microextraction fibre–water distribution constants of more hydrophobic organic compounds and their correlations with octanol–water partition coefficients

Fibre coating–water distribution constants ( K fw) of more hydrophobic chemicals were determined with six different solid-phase microextraction fibre types (including a polyoctylmethylsiloxane (C 8) prototype) by fibre exposure to agitated large-volume water samples lasting several days. The results obtained are comparable with K fw values obtained under dynamic conditions. Octanol–water partition coefficients ( K ow) were measured with the mixture of distributing substances to examine log K fw–log K ow relationships based on a consistent dataset. K fw values obtained with liquid polymer fibre coatings correlate reasonably well with the hydrophobicity of the test compounds (with decreasing sensitivity in the following order: 7 μm polydimethylsiloxane (PDMS)>100 μm PDMS>C 8>polyacrylate) whereas this is not the case with the PDMS–divinylbenzene (DVB) and Carbowax–DVB fibres, partially porous coatings which provide the highest K fw values for all substances tested.

A Gas Sample Pre‐concentration Device Based on Solid Phase Microextraction (SPME) and Temperature Programmed Desorption (TPD)

A sample pre‐concentration device, based on solid phase microextraction (SPME) fiber and temperature programmed desorption (TPD), was developed and tested in the analysis of volatile organic compounds. The pre‐concentrator device consists of a low dead volume quartz tube that houses the SPME fiber during the extraction/ desorption steps, a Ni:Cr heating element, and a programmable power supply. Compounds are extracted from air into the SPME fiber according to their affinity and solubility to the fiber material. Following this extraction step, samples are desorbed by a pre‐programmed temperature ramp for their subsequent detection. The SPME fiber was exposed and sample extracted for a pre‐determined amount of time (1 min, in this work). Because of the limited specificity of the stationary phase in SPME fibers towards the analyte, background interfering compounds are unavoidably co‐extracted during this process. A TPD step was then applied to sequentially desorb and detect analytes and interferences. The temperature ramp was designed so as to maximize temporal resolution between target analytes and background chemical interferences. The SPME/TPD pre‐concentrator was tested with a binary chemical system consisting of dimethyl‐methylphosphate (DMMP, a chemical warfare simulant) and toluene (a common commercial solvent). Analyte desorption was monitored on‐line with a quadrupole ion trap mass spectrometer. Five SPME fibers with different stationary phases were tested: polyacrylate (PA), polydimethylsiloxane (PDMS), carboxen–polydimethylsiloxane (CAR/PDMS), polydimethylsiloxane–divinylbenzene (PDMS/DVB), and carbowax/divinylbenzene (CW/DVB). Best results were obtained with the PDMS (100 µm) fiber. Two other SPME fibers, CW/DVB and CAR/PDMS, along with the TPD step, were also successful in the temporal resolution the of DMMP and toluene. The approach is rapid in that the extraction and desorption steps take less than 3 min. Implications and applications of the SPME/TPD system as a sample pre‐concentration step in handheld devices are discussed. The simplicity of the device makes it amenable to miniaturization by available microfabrication techniques.

Determination of phthalic monoesters in aqueous and urine samples by solid‐phase microextraction–diazomethane on‐fibre derivatization–gas chromatography–mass spectrometry

AbstractA solvent‐free analytical methodology for the determination of phthalic monoesters (MPs) with diazomethane on‐fibre derivatization using solid‐phase microextraction–gas chromatography–mass spectrometry (SPME–DOFD–GC–MS) was developed. Among the different SPME fibres evaluated, the polydimethylsiloxane/divinylbenzene (PDMS/DVB) proved to be the most suitable for the determination of four MPs. The diazomethane on‐fibre derivatization (DOFD) procedure was improved, avoiding diethyl ether as solvent. Equilibrium conditions were reached (15 min) and K′MP values were calculated. Under optimum MP extraction conditions (e. g. direct immersion, 4 mL of sample, 25°C extraction temperature, stirring at 1 100 rpm, 20 min extraction time, 10 min derivatization reaction, and pH = 1.5), trace level concentrations of MPs (0.3–8.6 ng/mL) were detected, allowing the simultaneous determination of phthalic diesters (DPs). The overall SPME–GC–MS precision was improved by using four deuterated internal standards. The developed analytical methodology was applied to different environmental water matrices and human urine samples at MP concentrations ranging from 0.1–538 ng/mL. The developed analytical procedure is robust (50 analyses with the same fibre), rapid (40 min), and of low cost, improving the conventional analysis methods in terms of analysis time, background levels, and cost.

Separation and determination of methyl tert-butyl ether and its degradation products by a laboratory-constructed micro-cryogenic chromatographic oven.

A laboratory-made micro-cryogenic chromatographic oven was mainly improved in size, which was controlled at 6 x 6 x 2.5 cm. A thermoelectric system was used to cool the capillary column instead of the traditional liquid cryogen. A cold block connected to the cryogenic module was directly solidified at room temperature with thermally conductive adhesive so that the uniformity of transferring heat was greatly improved, and the size of the system was reduced. Moreover, this system was inexpensive and convenient for both operation and control. The newly developed device coupled with headspace solid-phase microextraction (SPME) was successfully applied to the determination of methyl tert-butyl ether (MTBE) and its degradation products. During the analysis procedure, a 65 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber was used to extract MTBE and its degradation products. The extraction was controlled at 50 degrees C for 30 min and the NaCl content in the sample was maintained at 35%. The limits of detection (LODs) ranged from 0.006 microg mL(-1) (for MTBE) to 0.206 microg mL(-1) (for methyl acetate) and the relative standard deviations (RSD%) were below 4%. The spiked recoveries for the developed method were evaluated using various water samples as a matrix.

Solid-phase microextraction of human plasma samples for determination of sufentanil by gas chromatography-mass spectrometry.

A solid-phase microextraction (SPME) method has been developed for the quantitative analysis of sufentanil from human plasma by gas chromatography-mass spectrometry (GC-MS). The immersion SPME sampling technique was optimized for the extraction of sufentanil from plasma. The influence of the pH and the ionic strength of the sample on the extraction of the analytes by the SPME fiber were investigated. Sufentanil and fentanyl (internal standard) were extracted from plasma with a 65-microm polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber for 30 minutes using salting out agents in basic conditions. The calibration curve was linear over a concentration range of 6-50 ng/mL. Intraday and interday relative standard deviations were 3.6% and 10.6%, respectively. The limit of quantification was 6 ng/mL for a plasma volume of 1 mL. With regard to selectivity, simplicity, and low cost, the SPME method described should be useful for a rapid extraction of sufentanil from human plasma.

SPME applied to the study of volatile organic compounds emitted by three species of Eucalyptus in situ. Solid-phase micro extraction.

Headspace solid-phase microextraction coupled to gas chromatography/ion trap mass spectrometry-65 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) was used to identify and monitor the emission patterns of biogenic volatile organic compounds from leaves of Eucalyptus dunnii, Eucalyptus saligna, and Eucalyptus citriodora in situ. Short extractions (1 min) were performed every 30 min for periods of 8-10 h during 24 days taking advantage of the high capacity of this porous polymer coating. Forty-two compounds were detected and 20 identified in the headspace of E. saligna leaves, and 19 of 27 compounds were identified in the headspace of E. dunnii leaves. The emission pattern of (E)-beta-ocimene and rose oxide suggests that they may play a bioactive role in Eucalyptus.

Headspace solid phase microextraction for the analysis of the new antifouling agents Irgarol 1051 and Sea Nine 211 in natural waters

A simple and rapid extraction method based on headspace solid phase microextraction (HS-SPME) has been developed for the analysis of two antifouling agents, currently licensed for use in marine antifouling paints. Irgarol 1051 and Sea Nine 211 were extracted from aqueous solutions using polydimethylsiloxane–divinylbenzene (PDMS–DVB) 65 μm fiber and analyzed by gas chromatography (GC) with flame thermionic, electron capture and mass spectrometric detection. The extraction time, addition of Na 2SO 4 and the influence of organic matter, such as humic acid on extraction efficiency were examined in order to achieve a sensitive method. The optimized procedure was applied to spiked natural waters, such as sea water, river water and lake water in a concentration range of 0.5–50 μg l −1 in order to obtain the analytical characteristics. The linear calibration curve obtained ( R 2>0.990) for both analytes indicate that the presence of interfering compounds had no significant effect due to the high affinity of both analytes to the PDMS–DVB 65 μm fiber coating. Recoveries were in relatively high levels over >82% in all types of natural waters. The limits of detection (LODs) ranged from 0.002 to 0.030 μg l −1, depending on the detector and the compound investigated, with relative standard deviations in the range of 3–12% at all concentration levels tested. Finally, the proposed method was applied in real water samples from different marinas of Epirus region (NW Greece) in order to investigate its performance in precise and routine environmental analysis.

SIMULTANEOUS DETERMINATION OF FENTANYL AND MIDAZOLAM IN PLASMA USING DIRECT SOLID-PHASE MICROEXTRACTION BEFORE GAS CHROMATOGRAPHY–MASS SPECTROMETRY ANALYSIS

ABSTRACT We developed a rapid, specific, and sensitive solid-phase extraction method followed by gas chromatography–mass spectrometry analysis for the determination of fentanyl, midazolam or both drugs simultaneously in plasma samples. Various solid-phase microextraction fibres, extraction and desorption conditions were tested in the search of the best linearity, sensitivity and clean-up. The optimal solid-phase microextraction conditions were obtained with a new 65-µm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibre. Because of the high extraction selectivity and efficiency, the quantification limit for fentanyl and midazolam could be down to 0.8 ng mL−1 and 1 ng mL−1, respectively, for a plasma volume of 1 mL. The method described is sensitive enough for analysed fentanyl and midazolam in plasma samples for toxicological screening and therapeutic drug monitoring.

Determination of organochlorine pesticides by gas chromatography with solid-phase microextraction

A study of different extraction techniques for the determination of a selected group of organochlorine compounds in surface waters is presented. Comparison of liquid-liquid extraction (LLE) with solid-phase extraction (SPE) and solid-phase microextraction (SPME) with fibers of different polarity shows that SPME with a recently commercialised fiber of polydimethylsiloxane divinylbenzene allows these compounds to be determined in surface waters with good extraction efficiencies. Extraction time, effect of temperature, ionic strength and pH were optimised, allowing quantification in agricultural effluents in the range 1.0–60 ng·L−1.

Optimisation of a solid-phase microextraction method for synthetic musk compounds in water

A solid-phase microextraction method (SPME) for determining trace levels of synthetic musk fragrances in residual waters has been developed. Six polycyclic musks (cashmeran, phantolide, celestolide, traseolide, galaxolide and tonalide), and a macrocyclic musk (ambrettolide) have been analysed. A detailed study of the different parameters affecting the extraction process is presented. The main important factors affecting the microextraction process have been studied and optimised by means of a categorical factorial design. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using four different fiber coatings [polydimethylsiloxane (PDMS), Carboxen (CAR)–PDMS, PDMS–divinylbenzene (DVB) and Carbowax (CW)–DVB]. An extraction temperature of 100 °C sampling the headspace over the sample using CAR–PDMS or PDMS–DVB as fiber coatings were found to be the experimental conditions that lead to a more effective extraction. The method proposed is very simple and yields high sensitivity, with detection limits in the low pg/ml, good linearity and repeatability for all the target compounds. The total analysis time, including extraction and GC analysis, was only 45 min. The optimised method performed well when it was applied to waste water from an urban treatment plant.

Determination of delorazepam in urine by solid-phase microextraction coupled to high performance liquid chromatography

An SPME–HPLC–UV method for the determination of delorazepam, a representative benzodiazepine, in spiked human urine samples was developed for the first time. The performances of two commercially available fibers, a carbowax/templated resin (Carbowax/TPR-100) and a polydimethylsiloxane/divinylbenzene (PDMS/DVB), were compared, indicating the latter as the most suitable for urine samples analysis. All the aspects influencing adsorption (extraction time, pH, temperature, salt addition) and desorption (desorption and injection time, desorption solvent mixture composition) of the analyte on the fiber have been investigated. In particular, short extraction times were necessary to reach the equilibrium and very short desorption times were employed. The procedure required simple sample pre-treatment and was able to detect 5 ng/ml in spiked urine, regardless of the complexity of the matrix.

Gas chromatographic determination of glutaraldehyde in the workplace atmosphere after derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine on a solid-phase microextraction fibre

Glutaraldehyde is used primarily in hospital environments for the disinfection of various instruments (e.g., endoscopes). We describe in this paper the measurement of glutaraldehyde in a hospital environment using solid-phase microextraction. The method includes, prior to sampling, the adsorption of O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine on to the fibre (with polydimethylsiloxane–divinylbenzene). The fibre is then exposed to air, after which desorption is performed in the GC injection port. This process results in the formation of a stable derivative of the glutaraldehyde that is suitable for chromatographic purposes and detectable with classical detection methods, such as flame ionisation and electron-capture detection. We demonstrate that the procedure of adsorption, thermal desorption and derivatization is robust and reproducible. We were able to detect concentrations of 60 μg/m 3 (10 s sampling) or 6 μg/m 3 (120 s sampling) by electron-capture detection, and 80 μg/m 3 (120 s sampling) by flame ionisation detection. We compared our method to currently existing methods of glutaraldehyde measurement and highlighted several important advantages of the method.

Optimisation of headspace solid-phase microextraction for analysis of aromatic compounds in vinegar

Headspace solid-phase microextraction has been applied to the analysis of aroma compounds in vinegar. Silica fibre coated with Carboxen–polydimethylsiloxane was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, Carbowax–divinylbenzene, and polydimethylsiloxane–divinylbenzene, but its repeatability was low. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength, and sample volume were optimised using a two-level factorial design expanded further to a central composite design. This chemometric tool is very appropriate in screening experiments where the aim is to investigate several possibly influential and/or interacting factors. The extraction efficiency is inversely affected by the acetic acid content—an increase in the acetic acid concentration decreases the extraction efficiency. No interference is observed with the increase in content of polyphenols.

Determination of thymol in human plasma by automated headspace solid-phase microextraction–gas chromatographic analysis

A reliable and sensitive method was developed for determination of thymol in human plasma by automated headspace solid-phase microextraction (SPME). After enzymatic cleavage of thymol sulfate thymol was extracted by a 65 μm polydimethylsiloxane–divinylbenzene crimped fiber (Supelco) after addition of sodium chloride and phosphoric acid (85%). Desorption of the fiber was performed in the injection port of a gas chromatograph at 220°C (HP 5890; 50 m×0.2 mm I.D., 0.2 μm HP Innowax capillary column; flame ionization detection). Fibers were used repeatedly up to 40 analysis. The recovery was 5% after 35 min of extraction. The calibration curve was linear in the range of 8.1-203.5 ng ml −1 with a limit of quantitation (LOQ) of 8.1 ng ml −1. The within-day and between-day precision and accuracy were ≤20% at the LOQ and <15% at higher concentrations according to international guidelines for validation of bioanalytical methods. After administration of a thymol-containing herbal extract only thymol sulfate, no free thymol, could be detected in human plasma, thus analysis of thymol was after enzymatic cleavage of thymol sulfate. It is concluded that the newly developed automated method can be used in clinical trials on bioavailability and pharmacokinetics of thymol-containing herbal medicinal products.

Determination of chlorophenols by solid-phase microextraction and liquid chromatography with electrochemical detection

A solid-phase microextraction method has been developed for the determination of 19 chlorophenols (CPs) in environmental samples. The analytical procedure involves direct sampling of CPs from water using solid-phase microextraction (SPME) and determination by liquid chromatography with electrochemical detection (LC–ED). Three kinds of fibre [50 μm carbowax-templated resin (CW-TPR), 60 μm polydimethylsiloxane–divinylbenzene (PDMS–DVB) and 85 μm polyacrylate (PA)] were evaluated for the analysis of CPs. Of these fibres, CW-TPR is the most suitable for the determination of CPs in water. Optimal conditions for both desorption and absorption SPME processes, such as composition of the desorption solvent (water–acetonitrile–methanol, 20:30:50) and desorption time (5 min), extraction time (50 min) and temperature (40 °C) as well as pH (3.5) and ionic strength (6 g NaCl) were established. The precision of the SPME–LC–ED method gave relative standard deviations (RSDs) of between 4 and 11%. The method was linear over three to four orders of magnitude and the detection limits, from 3 to 8 ng l −1, were lower than the European Community legislation limits for drinking water. The method was applied to the analysis of CPs in drinking water and wood samples.

Focused microwave assistance for extracting some pesticide residues from strawberries into water before their determination by SPME/HPLC/DAD.

A novel and simple method for the determination of some pesticide residues in strawberries using both focused microwave-assisted extraction (FMAE) and solid-phase micro extraction (SPME), coupled with high-performance liquid chromatography (HPLC), has been developed. The pesticides were first extracted from strawberries with water and the assistance of focused microwaves at 30 W for 7 min. Then, an aliquot of the resulting aqueous extract was subjected to SPME with a 60-microm thick poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber for 45 min at room temperature, with the solution being stirred at 1000 rpm. The extracted pesticides on the SPME fiber were desorbed into the SPME/HPLC interface for quantitative analysis with a diode array detector (DAD). The whole sample pretreatment procedure before chromatographic analysis did not use any organic solvents or involve any blending or centrifugation steps. The five compounds (carbendazim, diethofencarb, azoxystrobine, napropamide, and bupirimate) were chosen because they cannot be analyzed easily by GC. The efficiency of this relatively fast procedure was comparable to that of previously reported methods, with detection limits at low microg/kg levels and linear responses in the range from 0.05 to 1 mg/kg of pesticide in strawberries, with RSDs between 3 and 7.3%, depending on the analyte. In all but one case results obtained by this method for field-incurred samples were comparable to those obtained with traditional methods.