Air sampling of organophosphate triesters using SPME under non-equilibrium conditions

Solid phase micro-extraction (SPME) was used to collect air samples of semi-volatile organophosphate triesters, a group of compounds that are commonly used as flame retardants/plasticisers and have therefore become ubiquitous indoor air pollutants. SPME is a simple sampling technique with several major advantages, including time-efficiency and low solvent consumption. Analyte losses also tend to be relatively low. In quantitative SPME, measurements are normally taken after the analyte has reached partitioning equilibrium between the fibre and the sample matrix. However, equilibrium sampling of semi-volatile compounds in air with SPME often takes several hours. Clearly, time-weighted average (TWA) sampling using SPME under non-equilibrium conditions could be considerably faster. So, in this study, the possibility of sampling organophosphate triesters under non-equilibrium conditions was tested. The most important variables proved to be the fibre coating and the air velocity during sampling. The highest uptake rate was obtained with polydimethylsiloxane (PDMS, 100 m). The rate for this fibre was 150-fold higher than obtained with PDMS/DVB and Carbowax/DVB, both 65 m. Contrary to theoretical expectations, the uptake rate appeared to be constant for all tested air velocities over the fibre surface >7 cm/s. These findings suggest that the uptake rate for non-equilibrium SPME sampling is independent of the sampling flow above this flow rate, which would considerably enhance the robustness and flexibility of the method. Applying this method for TWA sampling, with sampling periods of 1 h, detection limits lower than 2 ng/m³ for individual organophosphate esters were obtained.     

Simultaneous determination of semivolatile organic compounds in indoor air by gas chromatography-mass spectrometry after solid-phase extraction

A method is described for simultaneous determination of semivolatile organic compounds (SVOCs) in indoor air by gas chromatography-mass spectrometry (GC-MS). The selected 73 SVOCs were collected using combined adsorbents (quartz fiber filter disk and Empore disk) for 24 h at a 5.0 l/min flow rate. The SVOCs collected were extracted with acetone, concentrated, then analyzed by an internal standard method. Forty compounds (19 plasticizers and flame retardants; 19 insecticides; 1 synergist; and 1 fungicide) among the target SVOCs were determined accurately and precisely. The method of detection limits for these compounds were approximately 0.5 ng/m3 for most of the SVOCs. The collected SVOC samples could be stored for up to 1 month at 4 C in the refrigerator.     

Analysis of sulfur-containing compounds in ambient air using solid-phase microextraction and gas chromatography with pulsed flame photometric detection

A new analysis method for sulfur-containing compounds in air using solid-phase microextraction (SPME), gas chromatography and pulsed flame photometric detection (PFPD), SPME-GC-PFPD method, has been developed. The analysis method is simple, fast and easily performed. To demonstrate the usefulness and versatility of the method air samples collected in geothermal areas in Rotorua, at a muddy beach in Auckland (cities in New Zealand), and in a wastewater treatment plant were analysed. COS, H₂S, CS₂, SO₂, CH₃SH, (CH₃)₂S and CH₃(CH₂)₂CH₂SH were identified in the samples from Rotorua. It was noted that air quality in residential areas with respect to sulfur compounds was better than that around geothermal sources. Samples from the wastewater treatment plant contained COS, H₂S, CS₂, SO₂, CH₃SH, (CH₃)₂S and (CH₃)₂S₂. It was found that the emission of sulfur compounds was reduced in the course of the wastewater treatment process. The potential impact of the detected sulfur compounds on human health is briefly discussed.     

Evaluation of liquid-liquid microextraction using polypropylene microporous membranes for the determination of organophosphorus flame retardants and plasticizers in water samples

In this work, the suitability of the microporous membrane liquid–liquid extraction (MMLLE) technique for the concentration of several organophosphate esters (OPs) in water samples is assessed. Analytes were first extracted into a few microlitres of an organic solvent, immobilized in the pores of a hollow polypropylene membrane, and then determined by gas chromatography with nitrogen–phosphorus detection (GC–NPD). Main parameters controlling the efficiency of the extraction step were identified and their effects on the performance of the technique discussed. Under final working conditions, 2 cm long polypropylene membranes, containing about 7 μL of octanol in the pores, were dipped in a glass vial filled with 115 mL of water with a 30% of sodium chloride. Extractions were carried out for 12 h, at room temperature, under magnetic stirring. After that, analytes were recovered from the membrane with 0.2 mL of ethyl acetate. This extract was mixed with the internal standard (50 μL of a tripentyl phosphate solution in the same solvent) and finally reduced to ca. 50 μL. Overall enrichment factors for the optimized method ranged from 35 to 1400 times, and the achieved limits of quantification from 0.008 to 0.12 ng mL⁻¹, depending on the considered compound. Globally, the method showed an acceptable linearity and precision for all species, except for tris(2-ethylhexyl) phosphate (TEHP). Performance of the MMLLE approach is compared with that reported for other solid- and liquid-phase microextraction techniques and its suitability for the analysis of real water samples discussed.     

Determination of pyrethroid,organophosphate and organochlorine pesticides in water by headspace solid-phase microextraction

Simultaneous determination of pyrethroid, organophosphate (OP) and organochlorine (OC) pesticides in water was achieved with headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-electron-capture detection (GC-ECD). The parameters affecting HS-SPME of pesticides from water were optimized, including extraction temperature, sample and headspace volumes, and sodium chloride amounts. The effects of desorption temperature, desorption time, and position of the fibre in the GC inlet were also investigated. Extraction temperature was the most important factor affecting the recoveries of analytes, and the optimized temperature was 96°C. The addition of salt did not increase extraction efficiencies of the pesticides from the water. The optimized desorption conditions in the GC were as follows: desorption time of 10?min; desorption temperature of 260°C; and a 2?cm position of the fibre in the inlet. The method detection limits were in the low-ng/L level with a linearity range of 50–1000?ng/L for the OCs, 50–5000?ng/L for the OP, and 50–20?000?ng/L for the pyrethroids. These data demonstrated that HS-SPME is a sensitive method for the determination of pyrethroid, OC, and OP pesticides in water.     

Detection of organophosphate pesticides in human body fluids by headspace solid-phase microextraction (SPME) and capillary gas chromatography with nitrogen-phosphorus detection

Summary Organosphosphate pesticides have been found extractable by headspace solid-phase microextraction (SPME), and the best conditions of their extraction from human whole blood and urine samples have been investigated. The body fluid samples containing nine pesticides (IBP, methyl parathion, fenitrothion, malathion, fenthion, isoxathion, ethion, EPN and phosalone) were heated at 100°C in a septum-capped vial in the presence of various combinations of acid and salts, and SPME fiber was exposed to the headspace of the vial to allow adsorption of the pesticides before capillary gas chromatography (GC) with nitrogen-phosphorus detection. The heating with distilled water/HCl/(NH₄)₂SO₄/NaCl and with distilled water/HCl gave the best results for urine and whole blood, respectively. Recoveries of the nine pesticides were 0.8–10.6% except for phosalone (0.03%) for whole blood, and 3.8–40.2% for urine. The calibration curves for the pesticides showed linearity in the range of 50–400 ng/0.5 mL for whole blood except for malathion (100–400 ng/0.5 mL whole blood) and 7.5–120 ng/0.5 mL for urine except for phosalone (15–120 ng/0.5 mL urine) with detection limits of 2.2–40 ng/0.5 mL for whole blood and 0.8–12 ng/0.5 mL for urine.     

Determination of organophosphate flame retardants and plasticizers in sediment samples using microwave-assisted extraction and gas chromatography with inductively coupled plasma mass spectrometry

A procedure for the determination of 10 organophosphates, used as flame retardants and plasticizers, in sediment samples is presented. Microwave-assisted extraction (MAE) and gas chromatography with inductively coupled plasma mass spectrometry (GC-ICP-MS) were used for sample preparation and analytes determination, respectively. Influence of different variables on the performance of extraction and determination processes is thoroughly discussed. Temperature, type and amount of organic solvent showed a major effect on the yield of MAE. Regarding GC-ICP-MS detection, the combination of pulsed splitless injection with low radio frequency (rf) power, hard extraction conditions (referred to lens voltage) and addition of nitrogen (0.03 L min⁻¹) to the argon plasma provided the best sensitivity. Under final working conditions, recoveries between 78% and 105%, for samples spiked at different concentration levels, and limits of quantification from 2 to 4 ng g⁻¹ were achieved. Analysis of unspiked sediments confirmed the excellent selectivity of the proposed method for real-life polluted sample analysis.     

Passive sampling of airborne furan indoors by solid-phase microextraction

Furan may be formed in food under heat treatment and is highly suspected to appear in indoor air. The possible exposure to indoor furan raises concerns because it has been found to cause carcinogenicity and cytotoxicity in animals. To determine airborne furan, solid-phase microextraction (SPME) technique was utilised as a diffusive sampler. The Carboxen/Polydimethylsiloxane (CAR/PDMS, 75 μm) fibre was used, and the SPME fibre assembly was inserted into a polytetrafluoroethene tubing. Furan of known concentrations was generated in Tedlar gas bags for the evaluation of SPME diffusive samplers. After sampling, the sampler was inserted into the injection port of a gas chromatograph coupled with a mass spectrometer (GC/MS) for thermal desorption and analysis. Validation of the SPME device with active sampling by charcoal tube was performed side by side as well. The charcoal tube was desorbed by acetone before analysis with GC/MS. The experimental sampling constant of the sampler was found equal to (9.93 ± 1.28) × 10^?3 (cm³ min^?1) at 25°C. Furthermore, side-by-side validations between SPME device and charcoal tube showed linear relationship with r = 0.9927. The designed passive sampling device for furan has the advantages of both passive sampling and SPME technique and looks suitable for assessing indoor air quality.     

Determination of organophosphate flame retardants and plasticizers in lipid-rich matrices using dispersive solid-phase extraction as a sample cleanup step and ultra-high performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry

A fast, robust and highly sensitive analysis method for determination of trace levels of organophosphate ester (OPE) flame retardants and plasticizers in lipid-rich samples was presently developed, and based on ultra-high performance liquid chromatography-tandem mass spectrometry coupled to a positive atmospheric pressure chemical ionization source (UHPLC-MS/MS-APCI(+)). The target OPEs in the sample were extracted from the biota samples, such as egg and liver, by ultrasonic extraction, and cleaned up further by dispersive solid phase extraction (d-ESP). As a result, background contamination was largely reduced. Different dispersive ESP sorbents were tested and primary secondary amine (PSA) bonded silica sorbents showed the best recoveries for these target OPEs. The recoveries obtained were in the range 54–113% (RSD < 17%), with method limits of quantification (MLOQs) ranging between 0.06 and 0.29 ng/g in egg, and 0.05 and 0.50 ng/g w.w. in liver sample. The matrix effects (MEs) associated with using APCI(+) and ESI(+) sources were investigated. APCI(+) showed much less ion suppression than ESI(+) for the determination of these OPEs. For egg and liver samples, the APCI(+) ME values ranged from 40% to 94%, while ESI(+) ME values ranged from 0% to 36%. Although APCI(+) was used for the determination of OPEs, the ionization mechanism might mainly be a thermospray ionization process. This UHPLC-MS/MS-APCI(+) method showed good response linearity for calibration (R2 > 0.99). The proposed method was applied to real environmental bird egg and fish samples, where several OPE were quantifiable and different OPE patterns was observed between samples.     

Development of diffusive solid phase microextraction method for sampling of epichlorohydrin in air

Epichlorohydrin is used frequently in many industrial processes. Exposure to this pollutant could induce harmful effects. The present work developed a novel solid phase microextraction (SPME) method for time weighted average determination of epichlorohydrin in the air by GC/MS. CAR/PDMS in 0.5?cm retracted mode was selected and the effect of environmental parameters on sampling properties of SPME was examined. Experimental sampling rate for epichlorohydrin (8.89?×?10^?3?cm³/min) was slightly less than theoretical value (9.059?×?10^?3?cm³/min). There was no significant difference among sampling rates at different temperature and velocities but relative humidity had a significant effect on the sampling rate. Limit of detection for SPME method was 0.8?ng per sample, which is good enough in comparison with the NIOSH 1010 method. Comparison of the results between the developed SPME and the NIOSH 1010 method on standard test atmosphere and field showed satisfactory agreement (y?=?1.162x?+?1.8 r ²?=?0.992 and y?=?1.009x+0.76 r ²?=?0.98 respectively).     

A new optimization strategy for gaseous phase sampling by an internally cooled solid-phase microextraction technique

This study describes a new optimization strategy for internally cooled solid-phase microextraction based on a multivariate approach. The coating temperature was changed in an extraction while manipulating the extraction times to improve the extraction of compounds with different volatilities. Polycyclic aromatic hydrocarbons (PAHs) and phthalic acid esters (PEs) and adipate were used as model compounds in this study. The optimization strategy was in two steps: (1) multivariate optimization of extraction time and initial coating temperature and (2) multivariate optimization of total extraction time and the time required to cool the coating to a lower temperature as determined in step 1. The observed analytical response in relation to the coating temperature was found to be dependent on the analyte volatility and size. The optimized extraction condition for PEs was 23 min extraction while maintaining the coating at 140°C, followed by 7 min of cooling the coating at 10°C. For the PAHs the coating temperature was maintained at 60°C for the first 20 min and at 5°C in the last 20 min of extraction. Comparisons have been made between the proposed optimized conditions with the conventional internally cooled fiber approach and the results thoroughly discussed. The proposed optimization strategy was found to be more effective for all the analytes, especially for the semi-volatiles, compared to the conventional method.     

Flexibility of solid-phase microextraction for passive sampling of atmospheric pesticides

For low volatile pesticides, the applications of solid-phase microextraction (SPME) as an air sampler were reported with sampling time chosen in the linear stage of the sorption kinetics because of long equilibrium time. In these pre-equilibrium conditions, sampling rates (SRs) expressed as the volume of air sampled by the SPME sampler per unit of time, were used to estimate analytes concentrations in air. In the present study, to achieve good extraction performance and accurate calibration, the sorption kinetics of several pesticides with SPME were investigated in detail, with a focus on parameters influencing SRs. Linear air velocity was found to be the main parameter affecting SRs. For exposed fibers, with air velocities below 20–25 cm s⁻¹, SRs increased with increasing air velocity. When linear air velocity was equal to or greater than 25–30 cm s⁻¹, it had little effect on SRs. To improve the flexibility of SPME, different configurations of SPME were compared, i.e. different lengths of fibers exposed, retracted fibers, exposed fibers with grids. SRs were linearly proportional to exposed lengths of fibers. Using grids, lower SRs and wider calibration time range were achieved. SRs for retracted fibers were the lowest among the different experimented configurations. The accuracy of calibration was improved and more flexibility of SPME was provided.     

Sampling and sample-preparation strategies based on solid-phase microextraction for analysis of indoor air

Applications of solid-phase microextraction (SPME) to the sampling and analysis of volatile organic compounds in indoor air are reviewed, including a summary of quantification methods, coatings, compounds, concentrations, sampling locations and times, and detection limits. Strategies for on-site and off-site sampling and analysis, advantages and challenges associated with SPME for air sampling are discussed.     

Evaluation of capillary gas chromatography columns for the determination of free volatile amines after solid-phase microextraction

Summary Gas-liquid chromatographic capillary columns coated with 14% diphenyldimethylpolysiloxane, base-deactivated 5% diphenyldimethylpolysiloxane, or poly(ethylene glycol), and deactivated porous polymer for capillary gas-solid chromatography were evaluated for analysis of low-molecular-weight (C₁−C₉) amines. Solid-phase microextraction with a polydimethylsiloxane fiber was used for headspace sampling and for introduction of the sample into the gas chromatograph. As expected, basic of aliphatic gaseous or volatile aliphatic amines (carbon number: C₁−C₄). A thick (e. g. 3 μm) film of 5% diphenyldimethylpolysiloxane enabled determination of analytes in a wider molecular-weight range (C₃−C₉) with acceptable efficiency and resolution.     

Modelling of toluene solid-phase microextraction for indoor air sampling

Solid-phase microextraction (SPME) is a convenient and efficient sampling technique recently applied to indoor air analysis. We propose here a theoretical model of the adsorption kinetics of toluene on SPME fibre under static extraction conditions. We discuss the effects of sampling volume and initial concentration of analyte on the adsorption kinetics. This model is used to estimate the limits of detection taking into account operating conditions and to calculate theoretical calibration curves. Results of comparison with experimental data are encouraging: only 11% difference for calibration curves and 30% for the estimation of the limit of detection. On the basis of this kinetics model, the solid concentration gradient in the Carboxen coating was modelled with Fick’s second law of diffusion in unsteady-state mass-transfer mode. Mass diffusion from the gas sample to the SPME fibre was also investigated. It was shown that diffusion is the limiting step of the mass-transfer process in the static mode. Thus, the model developed, allows a better understanding of adsorption on Carboxen fibre and in the future could be a useful tool for cheap and time-saving development of SPME methods and the estimation of sampling performance. Figure PDMS/Carboxen SPME fibre (scanning electron microscopy – magnification x 220)     

Inside-tube solid-phase microextraction as an interlink between solid-phase microextraction and needle device for n-hexane evaluation in air and urine headspace

Monitoring the trace amount of chemicals in various samples remains a challenge. This study was conducted to develop a new solid-phase microextraction (SPME) system (inside-tube SPME) for trace analysis of n-hexane in air and urine matrix. The inside-tube SPME system was prepared based on the phase separation technique. A mixture of carbon aerogel and polystyrene was loaded inside the needle using methanol as the anti-solvent. The air matrix of n-hexane was prepared in a Tedlar bag, and n-hexane vapor was sampled at a flow rate of 0.1 L/min. Urine samples spiked with n-hexane were used to simulate the sampling method. The limit of detection using the inside-tube SPME was 0.0003 μg/sample with 2.5 mg of adsorbent, whereas that using the packed needle was 0.004 μg/sample with 5 mg of carbon aerogel. For n-hexane analysis, the day-to-day and within-day coefficient variation were lower than 1.37%, with recoveries over 98.41% achieved. The inside-tube SPME is an inter-link device between two sample preparation methods, namely, a needle trap device and an SPME system. The result of this study suggested the use of the inside-tube SPME containing carbon aerogel (adsorbent) as a simple and fast method with low cost for n-hexane evaluation.     

Suitability of solid-phase microextraction for the determination of organophosphate flame retardants and plasticizers in water samples

The feasibility of solid-phase microextraction (SPME) for the determination of several organophosphorus flame retardants and plastizicers in water samples by gas chromatography-nitrogen phosphorous detection (GC-NPD) is evaluated. These compounds have a wide range of polarities and volatilities and require a thorough optimisation of the different SPME parameters. Considering also possible contamination and carryover sources, the best compromise microextraction conditions were found to be direct extraction of 22 ml samples, containing 300 mg/ml of NaCl, with a PDMS-DVB coated fibre at room temperature. Although equilibrium was not achieved, an extraction time of 40 min allowed obtaining a good sensitivity (quantification limits between 0.010 and 0.025 ng/ml), comparable to that achieved by solid-phase extraction (SPE) of 1l samples, producing both similar values of precision and accuracy. Furthermore, the SPME method has shown to be free of matrix effects, avoiding the need of employing the standard addition procedure for quantification, and was suitable for the determination of eight of the nine considered compounds. Only tris-(2-ethylhexyl)-phosphate was neither determinable by SPME nor by SPE. Finally, the application of the developed methodology to the analysis of wastewater samples, showed that important concentrations of these compounds (up to 10 ng/ml) have been detected in treated sewage water, being discharged into the aquatic environment.     

Fiber introduction mass spectrometry: determination of pesticides in herbal infusions using a novel sol-gel PDMS/PVA fiber for solid-phase microextraction

An application of the direct coupling of solid-phase microextraction (SPME) with mass spectrometry (MS), a technique known as fiber introduction mass spectrometry (FIMS), is described to determine organochlorine (OCP) and organophosphorus (OPP) pesticides in herbal infusions of Passiflora L. A new fiber coated with a composite of poly(dimethylsiloxane) and poly(vinyl alcohol) (PDMS/PVA) was used. Sensitive, selective, simple and simultaneous quantification of several OCP and OPP was achieved by monitoring diagnostic fragment ions of m/z 266 (chlorothalonil), m/z 195 (alpha-endosulfan), m/z 278 (fenthion), m/z 263 (methyl parathion) and m/z 173 (malathion). Simple headspace SPME extraction (25 min) and fast FIMS detection (less than 40 s) of OCP and OPP from a highly complex herbal matrix provided good linearity with correlation coefficients of 0.991-0.999 for concentrations ranging from 10 to 140 ng ml(-1) of each compound. Good accuracy (80 to 110%), precision (0.6-14.9%) and low limits of detection (0.3-3.9 ng ml(-1)) were also obtained. Even after 400 desorption cycles inside the ionization source of the mass spectrometer, no visible degradation of the novel PDMS/PVA fiber was detected, confirming its suitability for FIMS. Fast (ca 20 s) pesticide desorption occurs for the PDMS/PVA fiber owing to the small thickness of the film and its reduced water sorption.     

Microwave-assisted headspace solid-phase microextraction for the rapid determination of organophosphate esters in aqueous samples by gas chromatography-mass spectrometry

The rapid and solvent-free determination of organophosphate esters (OPEs) in aqueous samples via one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS) analysis is described. Tri-n-butyl phosphate (TnBP) and tris-(2-ethylhexyl) phosphate (TEHP) were selected as model compounds for the method of development and validation. The effects of various extraction parameters for the quantitative extraction of these analytes by MA-HS-SPME were systematically investigated and optimized. The analytes, in a 20 mL water sample (in a 40 mL sample bottle containing 2 g of NaCl, pH 3.0), were efficiently extracted by a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber placed in the headspace when the system was microwave irradiated at 140 W for 5 min. The limits of quantification (LOQs) for TnBP and TEHP were 0.5 and 4 ng/L, respectively. Using the standard addition method, MA-HS-SPME coupled with GC-MS was utilized to determine selected OPEs in surface water and wastewater treatment plants (WWTP) influent/effluent samples. Preliminary results show that TnBP was commonly detected OPEs in these aqueous samples, the correlation coefficients (r²) of the standard addition curves were greater than 0.9822, indicating that the developed method appears to be a good alternative technique for analyzing OPEs in aqueous samples.     

Recent developments in solid-phase microextraction for on-site sampling and sample preparation

On-site sampling and sample preparation favor portable, solventless or even solvent-free techniques. Solid-phase microextraction (SPME) has these advantages. This review focuses on developments between 2007 and early 2011 in microextraction techniques for on-site sampling and sample preparation, including fiber SPME, stir-bar sorptive extraction (SBSE), thin-film microextraction (TFME) and different types of in-needle SPME. The major trends in on-site applications of SPME appear to be fiber and thin-film SPME, microextraction by packed sorbent (MEPS) and the sorbent-packed needle-trap device (NTD). We discuss and compare several aspects of these types of SPME in on-site applications. We also describe sorbent phases for SPME that benefit on-site applications. Finally, we provide a perspective on SPME-based techniques for on-site applications.