Headspace Gas Chromatographic Analysis Research Articles

Switchable hydrophilicity solvent-based hollow fibre liquid-liquid microextraction – headspace gas chromatography for determination of benzene and its derivatives in water samples


 
 
 
 A novel, cost-effective, simple and environmentally friendly method was developed for separating, preconcentrating and quantifying volatile analytes. That approach utilised switchable hydrophilicity solvent-based hollow fiber liquid-liquid microextraction in combination with headspace gas chromatography. The extraction was carried out from 1 l of water solution. 100 μl of nonanoic acid, immobilised within a polypropylene capillary, was selected as an extraction solvent. After the extraction, the capillary with the extract was transferred to a headspace vial, and headspace gas chromatographic analysis was performed. To facilitate the transition of volatile analytes to the headspace for subsequent analysis, nonanoic acid was converted to hydrophilic nonanoate by adding a sodium hydroxide solution.
 The effectiveness of the suggested strategy was demonstrated in the determination of benzene and its derivatives in water samples. Various parameters affecting the extraction and headspace gas chromatographic determination were investigated and optimised. Under the optimal conditions, the analytical characteristics of the proposed technique were determined.
 Using this approach, the limits of quantification for all analytes were found to be below the maximum acceptable concentration.
 
 
 

Investigation of operational fundamentals for vacuum-assisted headspace high-capacity solid-phase microextraction and gas chromatographic analysis of semivolatile compounds from a model solid sample.

Vacuum-assisted headspace solid-phase microextraction (Vac-HS-SPME) is a technique used to enhance SPME sampling of semi-volatile organic compounds. Here, it was combined with a high-capacity SPME Arrow, which features a larger volume of extraction phase and a more rugged configuration than traditional extraction fibers. An in-depth assessment of the critical parameters was conducted to achieve optimal extraction of representative compounds from a model solid sample matrix (Ottawa sand). Operational fundamentals investigated included the types of seals needed to create a leak-free environment under vacuum conditions; the magnitude of the vacuum applied and time needed to activate the Vac kinetics; order of sample vial preparation methods (VPMs); and other standard variables associated with extract analysis by gas chromatography-mass spectrometry. When exploring the limits of sample VPMs, results indicated an ideal workflow requires the solid sample to be spiked before sealing the vial, allow the sample to rest overnight, then apply vacuum at a pressure of -677mbar (out of -789mbar maximum possible vacuum with pump and compressor used), exerted on the vial for 90 s. This work provides the necessary workflow for the optimization of Vac-HS-SPME sampling of analytes from solid matrices.

Determination of six halogenated solvent residues in olive oil by headspace gas chromatography

The residual amount of halogenated solvents in olive oil is an important indicator of its quality. The National Olive Oil Quality Standard GB/T 23347-2021 states that the residual amount of individual halogenated solvents in olive oil should be ≤0.1 mg/kg and that the total residual amount of halogenated solvents should be ≤0.2 mg/kg. COI/T.20/Doc. No. 8-1990, which was published by the International Olive Council, describes the standard method used for the determination of halogenated solvents in olive oil. Unfortunately, this method is cumbersome, has poor repeatability and low automation, and is unsuitable for the detection and analysis of residual halogenated solvents in large quantities of olive oil. At present, no national standard method for determining residual halogenated solvents in olive oil is available in China. Thus, developing simple, efficient, accurate, and stable methods for the determination of residual halogenated solvents in olive oil is imperative. In this paper, a method based on automatic headspace gas chromatography was established for the determination of residual halogenated solvents, namely, chloroform, carbon tetrachloride, 1,1,1-trichloroethane, dibromochloromethane, tetrachloroethylene, and bromoform, in olive oil. The samples were processed as follows. After mixing, 2.00 g (accurate to 0.01 g) of the olive oil sample was added into a 20 mL headspace injection bottle and immediately sealed for headspace gas chromatography analysis. Blank virgin olive oil was used to prepare a standard working solution and the external standard method for quantification. The solvents used in the preparation of halogenated solvent standard intermediates were investigated and methanol was selected as a replacement for N,N-dimethylacetamide to prepare a halogenated solvent standard intermediate owing to its safety. The effects of different injection times (1, 2, 3, 4, 5, 6 s), equilibration temperatures (60, 70, 80, 90, 100, 110, 120 ℃), and equilibration times (4, 5, 8, 10, 20, 30, 40 min) of the headspace sampler on the detection of the residual amounts of the six halogenated solvents were investigated. The optimal injection time and equilibration temperature were 3 s and 90 ℃, respectively. The method demonstrated good analytical performance for the six halogenated solvents when the equilibration time was 30 min. A methodological study was conducted on the optimized method, and the results showed that the six halogenated solvents exhibited good linear relationships in the range of 0.002-0.200 mg/kg, with correlation coefficients of ≥0.9991. The limits of detection (LODs) and quantification (LOQs) of 1,1,1-trichloroethane and bromoform were 0.0006 and 0.002 mg/kg, respectively. The LODs and LOQs of chloroform, carbon tetrachloride, dibromochloromethane, and tetrachloroethylene were 0.0003 and 0.001 mg/kg, respectively. The average recoveries under different spiked levels were 85.53%-115.93%, and the relative standard deviations (n=6) were 1.11%-8.48%. The established method was used to analyze 13 olive oil samples available in the market. Although no halogenated solvents were detected in these samples, a limited number of samples does not represent all olive oils. Hence, monitoring residual halogenated solvents in olive oil remains necessary for its safe consumption. The LOQs of the method for the six halogenated solvents were significantly lower than that of the COI/T.20/Doc. No. 8-1990 standard method (0.02 mg/kg). In addition, the developed method can be conducted under short operation times with high precision and degree of automation as well as good accuracy. Thus, the proposed method is suitable for the determination and analysis of the residues of the six halogenated solvents in large batches of olive oil samples.

Para-Substituted O-Benzyl Sulfohydroxamic Acid Derivatives as Redox-Triggered Nitroxyl (HNO) Sources.

Nitroxyl shows a unique biological profile compared to the gasotransmitters nitric oxide and hydrogen sulfide. Nitroxyl reacts with thiols as an electrophile, and this redox chemistry mediates much of its biological chemistry. This reactivity necessitates the use of donors to study nitroxyl’s chemistry and biology. The preparation and evaluation of a small library of new redox-triggered nitroxyl sources is described. The condensation of sulfonyl chlorides and properly substituted O-benzyl hydroxylamines produced O-benzyl-substituted sulfohydroxamic acid derivatives with a 27–79% yield and with good purity. These compounds were designed to produce nitroxyl through a 1, 6 elimination upon oxidation or reduction via a Piloty’s acid derivative. Gas chromatographic headspace analysis of nitrous oxide, the dimerization and dehydration product of nitroxyl, provides evidence for nitroxyl formation. The reduction of derivatives containing nitro and azide groups generated nitrous oxide with a 25–92% yield, providing evidence of nitroxyl formation. The oxidation of a boronate-containing derivative produced nitrous oxide with a 23% yield. These results support the proposed mechanism of nitroxyl formation upon reduction/oxidation via a 1, 6 elimination and Piloty’s acid. These compounds hold promise as tools for understanding nitroxyl’s role in redox biology.

The significance in detecting and determining out-of-scope findings for volatile organic compounds in forensic casework

To provide an appreciation for identifying unknown peaks in headspace gas chromatography and a process for reporting additional information for volatile organic compounds (VOCs) in cases. VOCs are frequently abused as inhalants (gases or solvents). They are often abused due to their accessibility and low cost. VOCs are used in a variety of products including household and commercial items such as gasoline, compressed air duster products, nail polish, glues, paints, and varnishes. They are abused because they can be inhaled or insufflated. Abusing these substances can lead to serious health problems including the possibility of death due to chemical asphyxia and/or central nervous system depression. Routine testing procedures can be used to identify many such compounds. Cases for which VOCs were detected that were not in the routine scope of testing were identified during 2020 to 2022. The samples (all blood except for one gastric case) were originally analyzed using either headspace gas chromatography with flame ionized detection (GC/FID) and/or headspace gas chromatography/mass spectrometry (GC/MS). Where possible, if laboratory testing was performed in addition to volatile testing, volatile testing was performed first to limit evaporation of volatile compounds. Based on the results the sample either had further testing performed or an experienced forensic toxicologist was consulted to determine the next course of action. Unknown peaks identified through volatile toxicological testing include 1,1-Difluoroethane (DFE), Chlorodifluoromethane (Freon22), and components found in gasoline such as butane, pentane, benzene, etc. It is important to establish a process to determine when additional peak identification is needed. Frequently, this is provided through case history, but that is not always readily available. Depending on the sample matrix, the detected analytes, and their volatility, results were reported either qualitatively or quantitatively. Case reports for select samples will be discussed further to demonstrate the inherent value of this approach. Challenges exist with the use of headspace gas chromatography in the identification of unknown peaks. These peaks can provide vital information about a case. It is important to be vigilant when assessing such data since these peaks can often be missed or overlooked due to limits in the method. Identified unusual peaks in the chromatography should be interpreted with caution and additional case information needs to be sought. The significant findings from the out-of-scope headspace gas chromatography analysis can provide key toxicological information in cases when no other additional results are found.

Determination of methanol and fusel oils in various types of wines distributed in Korea.

The contents of methanol and fusel oils in various types of wines were determined using headspace-gas chromatography (HS-GC). The HS-GC analysis method showed good linearity, high precision and accuracy, and low LOQ and LOD values. The methanol content in 289 types of wines ranged from not detected (ND) to 333.84mg/kg, and was higher in Korean grape wines than in imported grape wines. Among fusel oils, the contents of 1-propanol (23.61-84.23mg/kg) and isobutanol (34.98-111.39mg/kg) were slightly higher in Korean wild grape wines, whereas that of isobutanol (ND to 55.26mg/kg) was slightly lower in Korean black raspberry wine than in the other wines. The contents of amyl alcohol were lower in Korean plum wine and Korean black raspberry wine than in all of the wines included in the present study, and highest in imported grape wines.

Sensitivity Increase in Headspace Analysis of Hydrocarbons in Water by Using Online Selective Elimination of Gas Extractant

In this study, a novel approach in headspace gas chromatographic analysis using the selective absorption of the gas extractant during concentration of the analytes was developed. The carbon dioxide used as the gas extractant was removed from the sample flow by passing it through a column packed with microdispersed sodium hydroxide granules. The analytical capabilities of the suggested method were illustrated by the determination of aliphatic and aromatic hydrocarbons in water. We established that this method allows the preconcentration of analytes in the gas phase to be increased proportionally to the volume ratios of the gas extractant before and after absorption, while the analyte limits of detection decrease 30-fold. For example, benzene can be detected in water at a concentration of 0.5 μg/L.

New and simple methods of determination partition coefficient and degree hydrolysis of tracer for estimating residual oil saturation by SWCTT technologies

SWCTT (Single-Well Chemical Tracer Test) actively used to determine the reservoir oil saturation as cost effective and quick method. To use this technology, the partition coefficients K and hydrolysis degree H of the tracer which determined experimentally in laboratories are essential for calculation of residual oil and estimation shut-off period of the well. In this paper, FTIR-spectroscopy and pH-metry were proposed for determination of partition coefficient of chemical tracer (ethyl acetate) and hydrolysis degree. Results obtained by these methods showed good correspondence with the data obtained by standard gas chromatographic analysis that confirms its applicability. All of these methods were used for the study of SWCTT parameters for four oilfields with different formation temperatures in the range 27–70 °C and formation water salinities up to 215,015 ppm. It was shown that oil-water partition coefficient of partitioning tracer increases with the rise of salinity. The apparent activation parameters of the hydrolysis reaction were determined by data on the degree of hydrolysis (pH-metry) and the concentration changes of tracer (head space gas chromatography analysis).

Isobutylene contamination of blood collected in 10-ml evacuated blood collection tubes with gray conventional rubber stoppers.

Dual-column headspace gas chromatographic analysis with two flame-ionization detectors is a commonly used analytical technique for forensic blood ethanol quantitation. This technique is also applicable to the identification and quantitation of other volatile organic compounds such as methanol in biological samples. Compound identification by retention time is limited to those compounds with known retention times programmed into the instrument method. Historically, an early-eluting peak from an unidentified compound has been observed in both chromatograms from antemortem blood samples analyzed for ethanol concentration with this technique. The unidentified compound's retention time matches that of methanol on one column but not on the second column. This previously unidentified compound has been identified as isobutylene. The proposed source of the isobutylene contamination historically observed in antemortem blood samples collected in 10-ml gray-top blood collection tubes is the conventional rubber stopper. Isobutylene was detected in deionized water stored in each of the seven lots of 10-ml blood tubes tested; the expiration dates of the tubes tested spanned the years 2002-2022. Misidentification of isobutylene as methanol is possible when using a single-column gas chromatographic system. The presence of isobutylene in blood collected in a gray-top collection tube does not represent laboratory contamination, is not an interferent with blood ethanol quantitation, and does not affect the ethanol concentration in the blood. A 0.150g/dl aqueous ethanol standard was stored in a gray-top tube to evaluate the potential impact of isobutylene on ethanol quantitation. The solution's average ethanol concentration measured after storage was 0.150g/dl.

The effect of sample temperature variations during sample preparation on measured blood ethanol concentration.

Since the accuracy of headspace gas chromatographic analysis of blood for ethanol concentration has been so well established over the past several decades, it has become commonplace in court proceedings to attack preanalytical handling of the blood samples including the lack of measuring sample temperature prior to sample preparation. The impact on measured ethanol concentration of allowing refrigerated (~4℃) samples varying amounts of time to equilibrate with room temperature, 24, 4, 3, 2, and 1h, prior to sample preparation was evaluated. Samples were diluted 1:10 with an internal standard using a diluter/dispenser and analyzed using headspace gas chromatography. The mean ethanol concentration measured for the sixteen samples at each of the five equilibration times was 0.153g/dl. The F-critical from the one-way ANOVA was 2.4937. The calculated F value was 0.4209. Additionally, the effect on measured ethanol concentration of having calibrators at different temperatures than case samples was investigated. Three groups were analyzed: all calibrators, controls, and samples given 24h to equilibrate with room temperature, all calibrators, controls, and samples prepared immediately after removal from refrigeration, and calibrators sampled immediately after removal from refrigerator with samples and controls allowed 24h to equilibrate with room temperature. The mean ethanol concentration measured for the thirty blood samples in each of the three groups was 0.197g/dl. The F-critical from the one-way ANOVA was 3.1013. The calculated F value was 0.0188. Measured ethanol concentrations were insensitive to the variations in preanalytical conditions evaluated in this study.

Development and Characterization of Inhaled Ethanol as a Novel Pharmacological Strategy Currently Evaluated in a Phase II Clinical Trial for Early-Stage SARS-CoV-2 Infection.

Inhaled administration of ethanol in the early stages of COVID-19 would favor its location on the initial replication sites, being able to reduce the progression of the disease and improving its prognosis. Before evaluating the efficacy and safety of this novel therapeutic strategy in humans, its characterization is required. The developed 65° ethanol formulation is stable at room temperature and protected from light for 15 days, maintaining its physicochemical and microbiological properties. Two oxygen flows have been tested for its administration (2 and 3 L/min) using an automated headspace gas chromatographic analysis technique (HS-GC-MS), with that of 2 L/min being the most appropriate one, ensuring the inhalation of an ethanol daily dose of 33.6 ± 3.6 mg/min and achieving more stable concentrations during the entire treatment (45 min). Under these conditions of administration, the formulation has proven to be safe, based on histological studies of the respiratory tracts and lungs of rats. On the other hand, these results are accompanied by the first preclinical molecular imaging study with radiolabeled ethanol administered by this route. The current ethanol formulation has received approval from the Spanish Agency of Medicines and Medical Devices for a phase II clinical trial for early-stage COVID-19 patients, which is currently in the recruitment phase (ALCOVID-19; EudraCT number: 2020-001760-29).

Impact of Polyunsaturated Fatty Acid Dilution and Antioxidant Addition on Lipid Oxidation Kinetics in Oil/Water Emulsions.

As consumers increasingly demand "cleaner" labels, one available strategy is diluting oils high in unsaturated fatty acids into more stable, more saturated oils, thus delaying lipid oxidation by decreasing free-radical propagation reactions between oxidized fatty acids and unsaturated lipids. The effect of diluting fish oil into medium-chain triglycerides (MCTs) on oxidative stability was investigated using lipid hydroperoxides and gas chromatography headspace analysis. Dilutions up to 1 in 20 of fish oil in MCT extended propanal formation from 1 to 6 days in Tween-80-stabilized oil-in-water emulsions. This protective effect was not observed in emulsions wherein the two oils were in separate droplets. Fish oil blended with high oleic sunflower oil (HOSO) also demonstrated a protective effect when the oils were in the same emulsion droplets but not in separate emulsion droplets. The present study indicates that dilution can be used to increase the oxidative stability of polyunsaturated fatty acids in oil-in-water emulsions.

Headspace gas chromatographic analysis of residual solvents in pharmaceuticals: comparison of two matrix media

Dimethylformamide (DMF) and a deep eutectic solvent choline chloride-ethylene glycol (ChCl-Eg) were investigated as potential matrix media for static headspace gas chromatographic (SHS-GC) determination of residual solvents in pharmaceuticals. Sample equilibration temperature, equilibration time and injection time were optimized. In the case of DMF 140°C equilibration temperature was applied. For ChCl-Eg equilibration temperature could not exceed 80°C as ChCl-Eg started to degrade at elevated temperatures. The higher equilibration temperature of DMF solutions favoured a transition of the analytes to the headspace and consequently resulted in lower detection limits of the analytes. Thus DMF has been considered a more suitable matrix medium than ChCl-Eg and was applied for the SHS-GC determination of residual solvents in pharmaceuticals.

Determination of ethanol concentration in alcoholic beverages by direct analysis in real time mass spectrometry (DART-MS)

Determination of the ethanol concentration in beverages remains an occasional request to forensic laboratories. While traditionally determined using headspace gas chromatography (HS-GC), this process involves lengthy run times and the need for specialized headspace sampling equipment for the GC system. The work presented here highlights a potential alternative to HS-GC analysis, using direct analysis in real time mass spectrometry (DART-MS). By incorporating a simple T-junction to the orifice of the mass spectrometer, analysis of the headspace of a beverage can be completed, resulting in measurement of the ethanol concentration in a matter of seconds with greater than 99% accuracy. This work presents the development of a method for ethanol quantitation as well as results from the analysis of both ethanol reference material standards and in-house created ethanol-containing solutions to evaluate the precision and accuracy of the technique. Analysis of ethanolic beverages via DART-MS is shown to be a rapid and reliable alternative to traditional analysis by HS-GC.

Изучение комплексообразования летучих органических соединений с β-циклодекстрином и его производными в водных растворах методом парофазного газохроматографического анализа

Изучение комплексообразования летучих органических соединений с β-циклодекстрином и его производными в водных растворах методом парофазного газохроматографического анализа

Gas chromatographic determination of some carboxylic acids: comparison between solution and headspace analysis

Direct and headspace gas chromatographic analysis is compared for the determination of lactic, oxalic, succinic, malic and citric acids. For better chromatographic behaviour, prior to GC analysis carboxylic acids were derivatized using BSTFA as a silylation reagent. Three solvents – acetone, diethyl ether and dimethylformamide – were tested as a derivatization medium and DMF was considered as the best. Derivatization conditions were optimized and analytical characteristics of the direct gas chromatographic determination of analytes in solutions were determined. The method was applied for the determination of citric acid in food. For the analytes dissolved in DMF, the headspace gas chromatographic determination was not sensitive enough. Concentrations of the derivates in the headspace were very low, thus the limits of detection were high and the method was not of practical use. On the other hand, headspace gas chromatography can be applied for identifying of carboxylic acids in solid samples.

Contrasting the solvation properties of protic ionic liquids with different nanoscale structure

The limiting activity coefficients of several hydrocarbons and aliphatic alcohols in protic ionic liquids: 2-hydroxyethylammonium nitrate (EOAN), propylammonium nitrate (PAN), butylammonium nitrate (BAN), and butylammonium thiocyanate (BASCN), were determined at 298K using gas chromatographic headspace analysis. The activity coefficients of hydrocarbons in EOAN turned out to be much higher than in BASCN or alkylammonium nitrates. The methylene group increments for the Gibbs free energies of solvation of various homological series in EOAN are also much higher than in BASCN, BAN, PAN as well as in aprotic ionic liquids or molecular solvents except water. Water-like solvation properties of EOAN are linked with the presence of a three-dimensional network of hydrogen bonds, high concentration of ion pairs, and the absence of nanoscale domain structure that exists in liquid alkylammonium salts and favors solvation of hydrocarbons in apolar domains. The sensitivity of solvation properties of PILs to their nanostructure suggests that the presence of apolar and polar domains in a liquid can be probed with the studies of solvation thermodynamics.

Rapid and quantitative determination of urea in milk by reaction headspace gas chromatography

In this paper, an efficient and robust technique based on reaction headspace gas chromatographic analysis for the quantification of urea in milk is presented, which is realized by measuring formed carbon dioxide from the enzymatic hydrolysis of urea under the catalysis of enzyme urease. It was observed that the headspace equilibration was finished in 40 min at 35 °C. The new technique was proved to be accurate (relative errors ≤7.17%) and precise (relative standard deviations ≤2.93%). In addition, compared with the reference spectrophotometric technique, the new technique has a higher sample throughput. The proposed approach is simple, fast and has the potential to be a practical tool for the batch analysis of urea in milk production and processing.

Determination of some short chain carboxylic acids in food by headspace gas chromatography

Headspace gas chromatographic analysis is suggested for the determination of acetic and propionic acids in aqueous media. Derivatization of the acids was accomplished by tributyl borate. The derivatization and headspace extraction were coupled into a single step. Analytical characteristics of the suggested technique at the optimized derivatization/headspace extraction conditions were determined. The technique was applied for the analysis of bakery products, ketchup, tomato paste and kefir.

Kraft lignin/cubic boron nitride hybrid materials as functional components for abrasive tools

In this study, the kraft lignin/cubic boron nitride hybrid materials have been obtained and characterized for the first time. The effectiveness of the combination of lignin and boron nitride was evaluated on the basis of Fourier transform infrared spectroscopy. Furthermore, it was confirmed that the addition of cubic boron nitride (cBN) improved the thermal stability of the inorganic-organic material. Upswing in thermal properties allowed to apply the prepared materials in preparation of model abrasive composites. Beneficial influence of the lignin/cBN filler was also proven by a noticeable decrease in the amount of harmful phenol released from the compositions during headspace gas chromatography analysis. Mechanical properties of the lignin/boron nitride hybrids and resin systems were investigated by the three-point flexural test. The obtained results show that the used additives can be promising materials for abrasive tools combining the good properties of lignin as a plasticizer and of cubic boron nitride as a filler which improves the thermal and mechanical properties of finished products and, at the same time, limits the negative impact on human health and environment.