Static Headspace Sampling Research Articles

Mixed aqueous solutions as dilution media in the determination of residual solvents by static headspace gas chromatography

Static headspace (HS) sampling has been commonly used to test for volatile organic chemicals, usually referred to as residual solvents (RS) in pharmaceuticals. If the sample is not soluble in water, organic solvents are used. However, these seriously reduce the sensitivity in the determination of some RS. Here, mixed aqueous dilution media (a mixture of water and an organic solvent like dimethyl formamide, dimethyl sulfoxide or dimethyl acetamide) were studied as alternative media for static HS-gas chromatographic analysis. Although it has been known that mixed aqueous dilution media can often improve sensitivity for many RS, this study used a systematic approach to investigate phase volumes and the organic content in the HS sampling media. Reference solutions using 18 different class 1, 2 and 3 RS were evaluated. The effect of salt addition was also studied in this work. A significant increase in the peak area was observed for all RS using mixed aqueous dilution media, when compared with organic solvents alone. Matrix effects related to the mixed aqueous dilution media were also investigated and reported. Repeatability and linearity obtained with mixed aqueous dilution media were found to be similar to those observed with pure organic solvents.

Static Headspace Sampling and Solid-Phase Microextraction for Assessment of Edible Oils Stability

Static headspace sampling and headspace solid-phase microextraction have been applied for the determination of the low molecular mass aldehydes—markers of edible oil oxidation. Preconcentration and determination conditions for the two procedures were optimized. LODs LOQs and repeatability of a standard mixture were established for all investigated compounds. Both methods of sampling were applied to the analysis of samples of rapeseed and sunflower oils. It appears that solid-phase microextraction is better than headspace sampling for the analysis of volatile oxidation products. Solid-phase microextraction can be conducted at a much lower temperature and has lower LOD values and better repeatability than headspace sampling.

Determination of aromatic compounds in eluates of pyrolysis solid residues using HS-GC–MS and DLLME–GC–MS

A method for the determination of 15 aromatic hydrocarbons in eluates from solid residues produced during the co-pyrolysis of plastics and pine biomass was developed. In a first step, several sampling techniques (headspace solid phase microextraction (HS-SPME), static headspace sampling (HS), and dispersive liquid–liquid microextraction (DLLME) were compared in order to evaluate their sensitivity towards these analytes. HS-SPME and HS sampling had the better performance, but DLLME was itself as a technique able to extract volatiles with a significant enrichment factor. HS sampling coupled with GC–MS was chosen for method validation for the analytes tested. Calibration curves were constructed for each analyte with correlation coefficients higher than 0.999. The limits of detection were in the range of 0.66–37.85 ng/L. The precision of the HS method was evaluated and good repeatability was achieved with relative standard deviations of 4.8–13.2%. The recoveries of the analytes were evaluated by analysing fortified real eluate samples and were in the range of 60.6–113.9%. The validated method was applied in real eluate samples. Benzene, toluene, ethylbenzene and xylenes (BTEX) were the compounds in higher concentrations. The DLLME technique coupled with GC–MS was used to investigate the presence of less volatile contaminants in eluate samples. This analysis revealed the presence of significant amounts of alkyl phenols and other aromatic compounds with appreciable water solubility.

Analysis of Unmetabolized VOCs in Urine by Headspace Solid‐Phase Microcolumn Extraction

Exposure to high concentrations of volatile organic compounds (VOCs) can lead to adverse health effects. Among VOCs, benzene is a haematotoxic substance that can induce acute myleoid leukaemia in occupational exposure, and has been classified as a carcinogen in humans by the International Agency for Research on Cancer. Other VOCs, trihalomethanes (chloroform, bromodichloromethane and dibromochloromethane) were detected in the urine of all persons attending a swimming pool, where the water was treated with chlorine. Tetrachloroethylene in urine of drycleaners has been used as biologic index of low-level exposure. A significant correlation was found between the environmental t r ich loroe thylene concent ra t ion and ur inary trichloroethylene concentration. BTEX (benzene, toluene, ethylbenzene and isomeric xylenes) have attained great relevance as ubiquitous pollutants of outdoor human environments and analysis of urine has been used for the evaluation of environmental exposures to these compounds. Similarly, styrene analysis in urine is a useful biological indicator of exposed workers. Generally, VOCs analyses involve either static or dynamic headspace (HS) sampling, followed by gas chromatographic separation and flame ionization (GCFID) or mass spectrometric detection (GC-MS). In the majority of the newly developed HS sample preparation techniques, the recovery of volatiles is based on sorption in a solid phase . Among them, equilibrium sampling techniques such as HS solid-phase microextraction, HS sorptive extraction , and a non-equilibrium sampling technique, HS solid-phase dynamic extraction, are available. In this study we have used the recently developed sampling technique, solid-phase microcolumn extraction (SPMCE), for the analysis of BTEX, styrene, chloroform, trichloroethylene and tetrachloroethylene in urine using GC-FID.

Non-Destructive Evaluation of Historical Paper Based on pH Estimation from VOC Emissions.

Volatile organic compounds (VOCs) emitted from materials during degradationcan be a valuable source of information. In this work, the emissions of furfural and aceticacid from cellulose were studied using solid-phase micro-extraction (SPME) incombination with gas chromatography-mass spectrometry. Two sampling techniques wereemployed: static headspace sampling using SPME for 1 h at 40 oC after 18-h samplepreparation at 80 oC in a closed glass vial, and contact SPME in a stack of paper (or abook). While a number of VOCs are emitted from paper under conditions of natural oraccelerated degradation, two compounds were confirmed to be of particular diagnosticvalue: acetic acid and furfural. The emissions of furfural are shown to correlate with pH ofthe cellulosic environment. Since pH is one of the most important parameters regardingdurability of this material, the developed method could be used for non-destructiveevaluation of historical paper.

Determination of volatile constituents in spirits using headspace trap technology

The use of headspace adsorbent traps in combination with gas chromatography was evaluated for the determination of volatile constituents (i.e. higher alcohols and other congeners of alcoholic fermentation) in spirits. The headspace trap technology comprises an enhanced static headspace system that allows enrichment and focusing of analytes on adsorbent traps prior to gas chromatographic separation. Extraction yields 35–55 times higher than those seen with static headspace sampling were achieved. An excellent agreement of analysis results in comparison to the European reference procedure was found ( R > 0.98, p < 0.0001). The fully automated headspace trap procedure requires only minimal sample preparation and is easy to apply.

Detection of age and insect damage incurred by wheat, with an electronic nose

Wheats of five storage ages and with 15 degrees of insect damage were evaluated and classified by the static-headspace sampling method using an electronic nose (E-nose). A commercial E-nose (PEN2) comprising 10 metal-oxide semiconductor (MOS) sensors was used to generate a typical chemical fingerprint of the volatile compounds present in the samples. Principal-component analysis (PCA) and linear-discriminant analysis (LDA) were applied to the generated patterns to achieve classification into the five groups of different storage-age wheats and the 15 groups of different degrees of insect-damaged wheat. The results obtained indicated that the E-nose could discriminate successfully among wheats of different age and with different degrees of insect damage.

Determination of Volatile Organic Compounds by Headspace Trap

A new analytical method for the determination of halogenated and aromatic volatile organic compounds in groundwater, mineral water, and drinking water at concentrations ranging between 1-10000 ng/L is developed. A new type of headspace sampler that combines static headspace sampling with a trap is used, yielding very low detection limits and good repeatability without carryover effects. An unexpected transformation of 1,1,2,2-tetrachloroethane into trichloroethene is observed and explained.

Single-Laboratory Validation of a Method for the Determination of Furan in Foods by Using Static Headspace Sampling and Gas Chromatography/Mass Spectrometry

A headspace gas chromatography/mass spectrometry method was developed and validated in-house for the determination of furan in foods. The method of standard additions with d4-furan as the internal standard was used to quantitate furan. The limit of detection and limit of quantitation (LOQ) values ranged from 0.2 and 0.6 nglg, respectively, in apple juice to 0.9 and 2.9 ng/g, respectively, in peanut butter. Recoveries were obtained at 0.5, 1, 2, and 3 times the LOQ. At 1, 2, and 3 times the LOQ, the recoveries ranged from 89.4 to 108%, and the relative standard deviations ranged from 3.3 to 17.3% for all the matrixes. For apple juice, chicken broth, and infant formula, the averaged coefficients of determination from the linear regression analyses were >0.99 with each food fortified at 0.5, 1, 2, and 3 times the LOQ. The coefficients of determination were >0.99 for green beans and 0.96 for peanut butter with the foods fortified at 1, 2, and 3 times the LOQ. Within-laboratory precision was determined by comparing the amounts of furan found in 18 samples by 2 analysts on different days with different instruments. For most of the foods, the difference between the amounts found by each analyst was <18%. The method was used to conduct a survey of >300 foods. The furan levels found ranged from none detected to 174 ng/g.

An Improved Approach for Accurate Quantitation of Benzene, Toluene, Ethylbenzene, Xylene, and Styrene in Blood

Widespread exposure to benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS) and the potential for this exposure to cause health effects drives the need to develop improved methods for measuring exposure. In this work, we demonstrate our latest assay for quantifying BTEXS in blood and characterize sources of both positive and negative biases. This method involves blood sample collection using common techniques followed by static headspace sampling using solid-phase microextraction and gas chromatography/mass spectrometry analysis. We found that the greatest and unexpected source of positive bias was from contamination of butyl rubber materials used in sample preparation consumables such as Vacutainer stoppers, syringe plungers, and sample vial septa. Conversely, the primary cause of negative bias observed was from the diffusion loss of BTEXS from blood during transfer into sample vials. By minimizing or eliminating these and other sources of bias, we improved method accuracy and precision to within 10% while maintaining low-picogram per milliliter detection. Furthermore, upon comparison of these results with those from other laboratories, we observe substantially lower blood BTEXS levels reported to date for nonoccupationally exposed nonsmokers. A relatively unbiased method, as such, will help elucidate any potential associations between adverse health effects and human exposure to low levels of BTEXS.

Separation science in perfume analysis

Perfumes generally consist of a volatile and a non-volatile fraction; they are often characterized through their volatile fraction, which is the subject of this article. In general, the term volatile fraction defines a mixture of volatile compounds that can be recovered due to their ability to vaporize spontaneously and/or through suitable techniques. The volatile fraction is therefore a general framework that includes headspace, essential oils, flavors, fragrances, aromas and extracts obtained by specific techniques. The number of conventional techniques usually adopted to analyze a perfume is limited: vacuum-, steamor hydrodistillation, solvent extraction off-line combined with distillation, simultaneous distillation-extraction (SDE), static and dynamic headspace (S–HS and D–HS) sampling for sample preparation, and capillary GC, capillary GC–MS or, to a lesser extent, capillary GC–FT–IR for analysis. Over the last ten to fifteen years, the perfume industry’s analytical strategies used to analyze the volatile fraction have evolved thanks to dramatic improvements in both of the fundamental steps of an analytical procedure: sample preparation and analysis. Based on new analysis methods and technologies, further approaches and strategies have been developed to investigate the composition and dynamics of several biological phenomena involved in perfumes. Several factors contribute to this methodological advance, alongside the use of electronics and information technology to manage analytical instrumentation, including:

Electronic nose for ham discrimination

In this paper, we report a specific application of an electronic nose based on a semiconductor thin film sensor array for the discrimination of different hams. The sensing elements of the sensor array were undoped and doped (Cr, Pt) SnO 2 thin films prepared by sputtering process. A system based on a static headspace sampling was used for the injection of the volatile compounds coming from the hams. Data analysis was performed by two pattern recognition methods: principal component analysis (PCA) and probabilistic neuronal network (PNN). The obtained results show that the electronic nose was able to identify the ham samples clearly.

Electronic nose for wine discrimination

An electronic nose based on metal oxide semiconductor thin-film sensors has been used to characterize and classify four types of red wines of the same variety of grapes which come from the same cellar. Two different systems for the injection of the volatile compounds coming from the wine, based on static and dynamic headspace sampling, were used. Sensor response generates a typical chemical fingerprint of the volatile compounds present in the wines. Data analysis was performed by two pattern recognition methods: principal component analysis (PCA) and probabilistic neuronal network (PNN). The results show that electronic nose was able to identify the above wine well.

Headspace gas chromatography-mass spectrometry: a fast approach to the identification and determination of 2-alkyl-3- methoxypyrazine pheromones in ladybugs

Static headspace sampling technique coupled with gas chromatography and mass spectrometry was used to investigate the presence of volatile 2-alkyl-3-methoxypyrazines in three different species of ladybugs of the Coccinellidae family. The species investigated were Coccinella septempunctata, Harmonia axyridis and Hippodemia convergens. 2-isopropyl-3-methoxypyrazine (IPMP) was identified in all three species with detectable levels of 2-sec-butyl-3-methoxypyrazine (SBMP) and 3-isobutyl-2-methoxypyrazines (IBMP) in only Hippodemia convergens and Harmonia axyridis species. Relative amounts of 2-alkyl-3-methoxypyrazines based on body mass showed that Hippodemia convergens had the highest levels of all three methoxypyrazines and Coccinella septempunctata the least.

Development of a headspace gas chromatographic test for the quantification of 1- and 2-bromopropane in human urine

A test procedure was developed for the detection and quantification of 1- and 2-bromopropane in human urine. 1-Bromopropane (1-BP) is a commonly used industrial solvent, and 2-bromopropane (2-BP) is often found as an impurity component in industrial grade 1-BP. Both compounds are a health concern for exposed workers due to their chronic toxicity. Bromopropanes have been associated with neurological disorders in both animals and humans. Sample preparation consisted of diluting urine with water and fortification with 1-bromobutane (1-BB), which was used as an internal standard; then each sample was sealed in a headspace vial. A static-headspace sampler (Teledyne-Tekmar Model 7000) was used to heat each sample at 75 °C for a 35-min equilibrium time. Quantification was by means of a gas chromatograph (GC) equipped with an electron capture detector (ECD) and a dimethylpolysiloxane (DB-1) capillary column. A recovery study using fortified urine samples at multiple concentrations (0.5–8 μg/ml) demonstrated full recovery; 104–121% recovery was obtained. Precision ranged from 5 to 17% for the 15–20 spiked samples used at each concentration, which were analyzed over multiple experimental trial days. The limit of detection (LOD) for this test procedure was approximately 2 ng/ml 1-BP and 7 ng/ml 2-BP in urine. A recovery study of 1- and 2-BP from fortified urine stored in vials appropriate for field collection was also completed. These results and other factors of the development and validation of this test procedure will be discussed.

TBA Production by Acid Hydrolysis of MTBE During Heated Headspace Analysis and Evaluation of a Base as a Preservative

AbstractAt room temperature (20° ± 3°C), purge and trap samplers provide poor sensitivity for analysis of the fuel oxygenates that are alcohols, such as tertiary butyl alcohol (TBA). Because alcohols are miscible or highly soluble in water, they are not efficiently transferred to a gas chromatograph for analysis. To improve the efficiency of transfer, the water in a purge and trap sampler can be heated. Alternatively, the sensitivity for TBA can be improved by preparing the sample in a heated static headspace sampler. In a heated water sample, the acid used as a preservative may cause chemical hydrolysis of methyl tertiary butyl ether (MTBE) to produce TBA. This effect is well illustrated in this paper using data collected by the U.S. Environmental Protection Agency Office of Research and Development on a plume of MTBE in California. Samples were analyzed using a static head‐space sampler heated to 80°C. The ground water samples were preserved in the field with HCl to a pH ≤ 2. The extent of MTBE hydrolysis to TBA during sample analysis varied from 19% to 87%; the average extent of hydrolysis was 59%. To confirm and document the importance of acid hydrolysis of MTBE at higher temperatures during sample preparation, the rate of hydrolysis of MTBE was measured at 80°C. At pH = 1, the rate of hydrolysis was 1.22/h, while the rate at pH = 2 was 0.15/h. Acid hydrolysis of MTBE during sample preparation in a heated headspace sampler can be avoided by preserving the sample with 1% (w/w) trisodium phosphate dodecahydrate (TSP) instead of using HCl, or by neutralizing the acid before analysis. In the presence of an acclimated microbial culture, TSP prevented biodegradation of MTBE, as well as benzene, toluene, ethylbenzene, and xylene compounds, in ground water at room temperature for 66 d. However, in a spike recovery experiment, TSP caused based catalyzed hydrolysis of bromomethane. It is not appropriate as a universal preservative.

Chemometric characterization of Italian wines by thin-film multisensors array and artificial neural networks

In the present work, nine samples of Italian wines (three white, three red and three rosè) from different denominations of origin have been analysed by the static headspace sampling method to attempt to classify them by chemometric characterization of the data obtained from a thin-film multisensor array. All wines have also been analysed to measure their ionic conductivity, pH and alcoholic content. An electronic nose comprising four metal oxide semiconductor thin-film sensors has been used to generate a typical chemical fingerprint (pattern) of the volatile compounds present in the wines. Principal component analysis and artificial neural networks were applied to the generated patterns to achieve various classification tasks. The classification performance of nine different pre-processing algorithms has been studied on the basis of three different sensor parameters and three different normalization techniques. The wine patterns generation with array sensor signals and the chemometric treatment are fast and simple by providing a recognition rate and a prediction rate as fairly high as 100% and 78%, respectively. These results can be considered satisfactory and acceptable, with the selected variables useful to differentiate these wines by their class.

Effects of gamma- and electron-beam irradiation on semi-rigid amorphous polyethylene terephthalate copolymers

Two semi-rigid amorphous polyethylene terephthalate copolymer materials (in both sheet and powder forms) containing 3% 1,4-cyclohexane dimethanol (CHDM) and 31% CHDM were irradiated at 5, 25 and 50 kGy at ambient temperature with a 60Co radiator or an electron-beam accelerator. After irradiation, volatiles were determined using static headspace sampling with capillary gas chromatography and mass selective detection or flame ionization detection (HS/GC/MSD or FID). Non-volatiles were extracted with 10% aqueous ethanol and 100% n-heptane food-simulating solvents, maintained at 40°C for up to 10 days. The non-volatiles in the materials and those migrating into the food-simulating solvents were determined by high-performance liquid chromatography (HPLC) with ultraviolet and/or photodiode array detection. The results obtained from the HS/GC/MSD suggest that no new chemicals were detected by either gamma- or e-beam irradiation when compared with non-irradiated specimens. The major volatiles in the copolymers were acetaldehyde and 2-methyl-1,3-dioxolane. The concentrations of acetaldehyde increased from 1.24–1.96 mg kg-1 to 1.94–3.65, 3.52–7.23 and 5.45–15.37 mg kg-1 after exposure to 5, 25 and 50 kGy doses, respectively. The concentrations of 2-methyl-1,3-dioxolane decreased from 2.49–5.26 mg kg-1 to 2.07–3.13, 1.33–2.14 and 0.64–2.24 mg kg-1 after exposure to 5, 25 and 50 kGy doses, respectively. The results of analysis of the copolymers for non-volatiles show that irradiation did not produce any new detectable non-volatile chemicals. A 5 kGy dose had no detectable effect on either copolymer. The 25 and 50 kGy doses had slightly different effects with respect to gamma- and e-beam irradiation on low MW oligomers. However, these increased doses did not significantly affect migration. The concentration of most low molecular weight oligomers migrating into 10% ethanol and 100% heptane was ⩽2 ng g-1 of each oligomer for both copolymers. The cyclic trimer migrating from the 3% CHDM copolymer was approximately 4 ng g-1; it was 3 ng g-1 for the 31% CHDM copolymer. The overall results suggest that irradiation significantly increased levels of acetaldehyde but had no effect on non-volatile compounds migrating into food simulants.

Identification and quantification of methyl jasmonate in leaf volatiles of Arabidopsis thaliana using solid-phase microextraction in combination with gas chromatography and mass spectrometry.

Static headspace sampling with solid-phase microextraction has been used in combination with GC-FID and GC-MS for the specific enrichment, identification and quantification of volatile methyl jasmonate secreted by wounded leaves of Arabidopsis thaliana. The microsample method of analysis was found to be precise, accurate, sensitive and rapid. The detection limit of the procedure is 1.5 ppb (approximately 1.3 ng) per injection, which is of adequate sensitivity to detect the natural baseline levels of methyl jasmonate (approximately 10-100 ng/g) present in plant tissues. The method can be applied to most plants, requires a minimum of sample material, and shows the additional advantage that it is suitable for automation and could thus be used for high-throughput screening.

Proposal for single and mixture biological exposure limits for sevoflurane and nitrous oxide at low occupational exposure levels.

Assessment of individual exposures to sevoflurane plus nitrous oxide (N(2)O) by biological monitoring of unmodified analytes in post-shift urine of exposed personnel. Anaesthetics in urine and breathing area were monitored in 124 subjects in 11 operating theatres. Passive samplers were collected after 2.5-7 h of exposure, at the same time as post-shift urinary samples, to evaluate the individual time-weighted average (TWA) exposures to sevoflurane and N(2)O. A static headspace sampler coupled with a gas chromatograph mass spectrometer was used for analytical determinations (sensitivity sufficient to reveal biological/environmental exposures of 0.1 microg/l(urine) and 50 ppb for sevoflurane, and 1 microg/l(urine) and 80 ppb for N(2)O). Median (range) post-shift urinary and environmental values were 1.2 microg/l(urine) (0.1-5.0) and 0.4 ppm (0.05-3.0) for sevoflurane ( n=107) and 10.9 microg/l(urine) (0.5-74.9) and 8.6 ppm (0.2-123.4) for N(2)O ( n=121) (all low-exposure range). At log-log regression, urinary levels closely correlated with environmental data (sevoflurane, r(2)=0.7538; N(2)O, r(2)=0.8749). Biological equivalent limits (BELs) based on National Institute for Occupational Safety and Health (NIOSH) TWA exposure limits, calculated as means of regression slope and y-intercept, were 3.6 microg/l(urine) for sevoflurane (corresponding to 2 ppm) and 22.3 microg/l(urine) for N(2)O (corresponding to 25 ppm). Individual "mixture BELs", which we calculated by applying the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) mix formula to biomarker values and using the obtained NIOSH-based BELs as a reference, closely correlated with mixture TLVs (rho=0.816, Lin's concordance test). CONCLUSIONS. We propose urinary sevoflurane as a new, specific, internal dose biomarker for routine biological monitoring of personal exposures among operating-theatre personnel, and use of reliable "mixture BELs" to provide safer levels of internal exposure for workers exposed to mixtures of sevoflurane and N(2)O, and conceivably also to other mixtures of toxicants with possible additive effects.