Method for improving accuracy in full evaporation headspace analysis

We report a new headspace analytical method in which multiple headspace extraction is incorporated with the full evaporation technique. The pressure uncertainty caused by the solid content change in the samples has a great impact to the measurement accuracy in the conventional full evaporation headspace analysis. The results (using ethanol solution as the model sample) showed that the present technique is effective to minimize such a problem. The proposed full evaporation multiple headspace extraction analysis technique is also automated and practical, and which could greatly broaden the applications of the full‐evaporation‐based headspace analysis.     

Rapid determination of furfural in biomass hydrolysate by full evaporation headspace gas chromatography

This paper reports a full evaporation (FE) headspace gas chromatographic (HS-GC) method for rapid determination of furfural in the biomass hydrolysate. The data show that a near-complete mass transfer of furfural in the sample from biomass hydrolysate to the vapor phase (headspace) was achieved within 3 min at 105°C when a very small (<40 μL) sample was added to a 20 mL headspace sample vial. The acid-catalyzed furfural decomposition under these conditions was negligible. The furfural in the vapor phase was then determined by HS-GC using a flame ionization detector. The results showed that the method has an excellent measurement precision (RSD<0.5%) and accuracy (recovery=100.2±1.7%) for furfural quantification in carbohydrate hydrolysate samples. The method requires no sample pretreatment, so it is simple, rapid and accurate, and suitable for applications in lignocellulosic biomass conversion to fuel ethanol or other high value-added products.     

Determination of residual monomer in polymer latex by full evaporation headspace gas chromatography

This study demonstrated a full evaporation (FE) headspace gas chromatographic technique for the determination of residual monomer in methyl methacrylate (MMA) polymer latex. A very small amount (approximately 10-30 mg) of latex was added to a sealed headspace sample vial (20 ml). A near-complete monomer mass transfer from both liquid (aqueous phase) and solid phase (polymer particles) to the vapor phase (headspace) is achieved within 5 min at a temperature of 110 degrees C. The method eliminates sample pretreatment procedures such as the solvent extraction. Thus, it avoids the risk of polymer deposition on the GC system caused by a directly injection of extraction solvent in the conventional GC monomer analysis. The present method is simple, rapid, and accurate.     

Novel headspace gas chromatographic method for determination of oxalate in oxygen delignification liquor

A novel headspace gas chromatographic (HS-GC) method is demonstrated for an indirect determination of oxalate in oxygen delignification liquors. A small volume (50-100 microL) of liquor sample is introduced into a sampling vial that contains 1.0 mL of 2 mol/L sulfuric acid. After removal of carbon dioxide (generated from carbonate in the acidic medium) by heating, the sample was mixed with a 0.5 mL of 0.02 mol/L potassium permanganate solution in a closed testing vial. At an elevated temperature (70 degrees C), the oxalate in the sample is rapidly converted to carbon dioxide by reacting with permanganate. The carbon dioxide in the headspace can be measured by gas chromatography with a thermal conductive detector. Using a multiple headspace extraction (MHE) measurement technique, the kinetics of formation of the carbon dioxide from the other organic species in the sample can be determined, and thus a correction can be made for minimizing the interferences. The present method is simple, accurate and can be easily automated.     

Determination of epoxy groups in epoxy resins by reaction-based headspace gas chromatography

This work reports on a new method for the determination of epoxy groups in epoxy resins by reaction-based headspace gas chromatography (HS-GC). After epoxy resins reacted with hydrochloric acid (HCl) solution, the remaining HCl reacted with bicarbonate solution in a closed headspace vial to form carbon dioxide that was measured by HS-GC. It was found that the first reaction can be finished in 30 min at room temperature and the second reaction, together with headspace equilibration, can be achieved within 15 min at 60 °C. The results showed that the method has a good precision and accuracy, in which the relative standard deviation in the repeatability measurement was 4.20%, and the relative differences between the data obtained by the HS-GC method and the reference method were within 8.04%. The present method is simple, efficient, and suitable for the used in the epoxy resin related research and applications.     

Elimination of matrix effects for static headspace analysis of ethanol.

The intention of this work was to develop a simple and fast procedure for a determination of small amounts of ethanol in aqueous protein containing solutions based on combined headspace gas chromatography. In order to provide for short analysis time static headspace methodology was considered for this purpose. In this context the influence of the matrix composition onto the analytical results has been established and internal standardization as well as a full evaporation technique have been evaluated as promising alternatives for a compensation of matrix effects. With respect to speed of analysis, simplicity of sample handling as well as the quality of the analytical performance parameters, precision and accuracy, the full evaporation technique proved to be superior. Thus, the static equilibration of a 20 microliters sample aliquot in a conventional headspace sample vial for 5 min at 100 degrees C is sufficient to obtain equilibrium conditions for gas chromatographic analysis. The accuracy of this method was verified by robust regression analysis and exhibited excellent robustness within the required limits of sample composition ranging from 0 to 20% (w/w) protein content and up to 5 g/l salt content.     

Determination of the residual ethanol in hydroalcoholic sealed hard gelatin capsules by static headspace gas chromatography with immiscible binary solvents

Static headspace gas chromatography (HS-GC) with immiscible binary solvents is described to quantitatively determine the residual ethanol used to seal the hard gelatin capsules by liquid encapsulated and microspray sealing (LEMS; cfs 1200, Greenwood, SC, USA). The effects of decane, dodecane, heptane, 0.1 M HCl, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidinone and dimethyl sulfoxide on the method sensitivity are compared. It is observed that the ethanol headspace concentrations can be increased by fourfolds when aliphatic hydrocarbon solvents are added into the aqueous sample solutions in a HS vial. In addition, a mathematic model based on the concentration equilibriums of liquid–liquid and liquid–gas phases is derived to quantitatively describe the ethanol headspace concentrations versus the volumes of the aliphatic hydrocarbon solvents. The proposed model fits well to the experimental data. The impacts of the oven temperatures and vial equilibration times on the ethanol headspace concentrations are also investigated. Furthermore, the potential interferences of the capsule placebo and hard gelatin capsule shells on the selectivity and quantitation of the method are discussed. The linearity is validated from 5 μg/mL to 500 μg/mL. The limit of quantitation is 5 μg/mL. The accuracy is determined to be 100.8 ± 6%. Finally, this method is successfully used to determine the residual ethanol in the sealed capsules of 5 mg and 10 mg developmental Drug A, and 100 mg and 200 mg developmental Drug B.     

Comprehensive headspace gas chromatographic analysis of denaturants in denatured ethanol

To discourage consumption, ethanol is often denatured using both volatile (e.g., methyl ethyl ketone and isopropanol) and nonvolatile (e.g., denatonium benzoate) chemical substances. As a result, the analysis of denatured ethanol samples is usually performed by multiple techniques such as gas chromatography for the volatile denaturants and liquid chromatography for the nonvolatile ones. However, the need for multiple techniques increases the cost of analysis and forms a severe obstruction for on‐site product control. Using the full evaporation technique combined with gas chromatography and flame ionization detection, only one analytical methodology has to be used here to determine both volatile and nonvolatile denaturants in denatured ethanol. Denatonium benzoate is determined as benzyl chloride following an in‐vial reaction. Compared to conventional techniques, the novel method performs equally well, but it is simpler to apply. At the same time, drawbacks of alternative methods are circumvented such as equilibration issues and alterations to the stationary phase when using liquid chromatography with ion pairing agents or matrix effects when applying static headspace gas chromatography. The developed method showed good linearity, repeatability, and recovery toward all analytes and was applied to the analysis of commercial denatured ethanol for disinfection and ethanol‐based windscreen washer fluids.     

Determination of total sugar content in lignocellulosic hydrolysates by using a reaction headspace gas chromatographic technique

This paper investigates a new analytical technique for the quantitative detection of total sugar content in lignocellulosic hydrolysates by reaction headspace gas chromatography (HS-GC). By detecting the carbon dioxide (CO₂) generated from the reaction between sugars in lignocellulosic hydrolysates and potassium dichromate, the total sugar content in lignocellulosic hydrolysates can be quantified. The data illustrate that the conversion of sugars in lignocellulose hydrolysates can be achieved under the given conditions (at 90 °C for 30 min), the relative standard deviation of this HS-GC technique in the total sugar content determination was within 3.35%, and the measured total sugar content in 15 lignocellulose hydrolysate samples closely matched those measured by the reference spectrophotometric technique (relative differences <7.69%). The present technique is efficient, reliable and suitable to be used in the total sugar content quantification in lignocellulose hydrolysate related research and process control.     

Rapid determination of methanol in black liquors by full evaporation headspace gas chromatography

This paper reported a full evaporation headspace gas chromatographic (GC) technique for determination of methanol content in black liquors (pulping spent liquor). In this method, a very small volume (10-20 microL) of liquor sample is introduced into a headspace sample vial (20 mL) and heated up to a temperature of 105 degrees C. A near-complete mass transfer of methanol from the liquid phase to vapor phase (headspace), i.e., a full evaporation, can be achieved within 3 min. The methanol in the headspace of the vial is then measured by GC. The present method is simple, rapid and accurate.     

Comparison of four extraction methods for analysis of volatile hop‐derived aroma compounds in beer

The volatile organic compound profile in beer is derived from hops, malt, yeast, and interactions between the ingredients, making it very diverse and complex. Due to the range and diversity of the volatile organic compounds present, the choice of the extraction method is extremely important for optimal sensitivity and selectivity. This study compared four extraction methods for hop‐derived compounds in beer late hopped with Nelson Sauvin. Extraction capacity and variation were compared for headspace solid‐phase micro extraction, stir bar sorptive extraction, headspace sorptive extraction, and solvent‐assisted flavor evaporation. Generally, stir bar sorptive extraction was better suited for acids, headspace sorptive extraction for esters and aldehydes, while headspace solid‐phase microextraction was less sensitive overall, extracting 40% fewer compounds. Solvent‐assisted flavor evaporation with dichloromethane was not suitable for the extraction of hop‐derived volatile organic compounds in beer, as the profile was strongly skewed towards alcohols and acids. Overall, headspace sorptive extraction is found to be best suited, closely followed by stir bar sorptive extraction.     

Analysis of nonvolatile species in a complex matrix by headspace gas chromatography

This study developed a phase reaction conversion (PRC) headspace gas chromatographic (HS-GC) technique for the measurements of nonvolatile species in liquid or solid samples. The technique is demonstrated by the measurements of carbonate in aqueous carbonate solutions and in kraft pulp mill liquor samples. A very small amount of sulfuric acid (volume of 0.5 ml, concentration of 2 mol/l) is used to acidify a sample of less than 300 microl in volume and convert the dissolved carbonate into carbon dioxide (gas) in a sample vial (reactor) that is analyzed by thermal conductivity detection through a headspace sampler. The carbonate concentrations measured by PRC-HS-GC in seven kraft liquor samples agree very well with those measured using a coulometric and a titrametric method. Simultaneous analysis of multiple species was also conducted to demonstrate the versatility of the method. The present method is very simple, rapid, reliable, accurate, and fully automated. It can be applied to analyze other nonvolatile species in various industrial and environmental samples.     

Determination of epichlorohydrin and 1,3-dichloro-2-propanol in synthesis of cationic etherifying reagent by headspace gas chromatography

This study demonstrates a headspace gas chromatographic(HS-GC) technique for the determination of residual epichlorohydrin (ECH) and generated 1,3-dichloro-2-propanol (DCP) in synthesis process of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHTAC). By a weight-based sampling method, coupled with significant dilution in 15.8% sodium sulfate and 0.1% silver nitrate mixed solution rapidly, the sample for HS-GC analysis is prepared. Based on the reaction stoichiometry, the conversion (R) of CHTAC during the synthesis process can be calculated from sampling weight and GC peak area. The results showed that the method has a good measurement precision (RSD<2.5%) and accuracy (recovery=101-104%) for the quantification of both ECH and DCP in the process samples. The present method is simple and accurate, which can be used for the efficient determination of the CHTAC conversion in the synthesis research.     

顶空气相色谱法测定化妆品中15种挥发性有机溶剂残留

建立了化妆品中15种挥发性有机溶剂残留的顶空气相色谱测定方法。样品经60 ℃、30 min静态顶空后,采用气相色谱-氢火焰离子化检测器进行检测,外标法定量。加标回收试验结果表明: 15种挥发性有机溶剂残留平均回收率为62.8%～116%,相对标准偏差均小于5%。方法的检出限为0.09～0.68 mg/kg。该方法可有效克服基体干扰,一次进样可同时分离和测定化妆品中15种挥发性有机溶剂,准确灵敏,简单快速,适用于化妆品中挥发性有机溶剂残留的检测。     

Solid-phase microextraction coupled with gas chromatography-ion trap mass spectrometry for the analysis of haloacetic acids in water

Headspace solid-phase microextraction (SPME) was studied as a possible alternative to liquid-liquid extraction for the analysis of haloacetic acids (HAAs) in water. The method involves derivatization of the acids to their ethyl esters using sulphuric acid and ethanol after evaporation, followed by headspace SPME with a polydimethylsiloxane fibre and gas chromatography-ion trap mass spectrometry (GC-IT-MS). The derivatization procedure was optimized: maximum sensitivity was obtained with esterification for 10 min at 50 degrees C in 30 microl of sulphuric acid and 40 microl of ethanol. The headspace SPME conditions were also optimized and good sensitivity was obtained at a sampling temperature of 25 degrees C, an absorption time of 10 min, the addition of 0.1 g of anhydrous sodium sulfate and a desorption time of 2 min. Good precision (RSD lower than 10%) and detection limits in the ng l(-1) range (from 10 to 200 ng l(-1)) were obtained for all the compounds. The optimized procedure was applied to the analysis of HAAs in tap water and the results obtained by standard addition agreed with those of EPA method 552.2, whereas discrepancies due to matrix interferences were observed using external calibration. Consequently, headspace SPME-GC-IT-MS with standard addition is recommended for the analysis of these compounds in drinking water.     

Rapid determination of ethanol in fermentation liquor by full evaporation headspace gas chromatography

This paper reports a full evaporation (FE) headspace gas chromatographic (GC) method for rapid determination of ethanol in fermentation liquor. The data show that ethanol in the fermentation liquor was transferred to the vapor phase (headspace) almost completely within 3 min at a temperature of 105 °C when a very small volume (<50 μL) of sample was directly added to a sealed headspace sample vial (20 mL). The ethanol in the vapor phase was then measured by headspace GC using a flame ionization detector. The results show that the present method has an excellent measurement precision (RSD = 1.62%) and accuracy (recovery = 98.1 (±1.76%)) for the ethanol quantification in fermentation liquors. The method requires no sample pretreatment and is very simple and rapid.     

Multiple headspace single-drop micro-extraction for quantitative determination of lactide in thermally-oxidized polylactide

Single-drop micro-extraction (SDME), an emerging micro-extraction technique, was combined with multiple headspace (MHS) extraction to allow quantitative determination of lactide in thermally-oxidized polylactide. Different solvents, drop sizes and extraction times were tested to obtain best extraction efficiency and the method was further developed to obtain a linear regression plot for the multiple extractions. The combination of SDME and MHS extraction offered several advantages over traditional liquid-solid and headspace extraction techniques. No concentration step was needed and loss of volatiles was prevented as the ageing and extraction were performed in a closed system. Matrix effects, that disturb the quantitation of analytes in solid samples, were removed by the multiple headspace extraction.     

Exploring multiple‐cumulative trapping solid‐phase microextraction for olive oil aroma profiling

Headspace solid‐phase microextraction is a solvent‐free sample preparation technique that is based on the equilibrium among a three‐phase system, i.e., sample‐headspace‐fiber. A compromise between sensitivity and extraction time is usually needed to optimize the sample throughput, especially when a large number of samples are analyzed, as usually the case in cross‐samples studies. This work explores the capability of multiple‐cumulative trapping solid‐phase microextraction on the characterization of the aroma profiling of olive oils, exploiting the automation capability of a novel headspace autosampler. It was shown that multiple‐cumulative solid‐phase microextraction has the potential to improve the overall sensitivity and burst the level of information for cross‐sample studies by using cumulative shorter extraction times.     

Multiple headspace single-drop microextraction-a new technique for quantitative determination of styrene in polystyrene

Single-drop microextraction (SDME), an emerging miniaturised extraction technique, was for the first time combined with multiple headspace extraction (MHE) to enable the quantitative determination of volatiles in solid matrixes by SDME technique. The concept of multiple headspace single-drop microextraction (MHS-SDME) was then applied for quantitative determination of styrene in polystyrene (PS) samples. Good linearity for the multiple headspace extraction was obtained when the migration of styrene was facilitated by grinding the samples and incubating them for 1 h at 150 degrees C prior the first extraction. Two microlitres of butyl acetate was used as the single-drop microextraction solvent and the extraction time was 5 min per cycle. The relative standard deviation (RSD) for single-drop microextraction of styrene standard at n=6 was 7.6%. Linearity was shown for styrene concentrations between 0.005 and 0.75 microg/ml (R2=0.999). This corresponds to total amount of styrene between 0.1 and 15 microg. The limit of quantitation for styrene standard at S/N 10 was 0.005 microg/ml. The developed method was validated against and showed good agreement with an earlier reported dissolution-precipitation method.     

Development of a static headspace gas chromatographic/mass spectrometric method to analyze the level of volatile contaminants biodegradation

Volatile compound biodegradation analysis usually requires the time-consuming step of extraction of the analytes from the matrix using organic solvents or costly radioactive-compounds. Thus, it is desirable to have a simple and fast technique to generate a good evaluation of bacterial biodegradation. The goal of this research was to develop a methodology on the basis of static headspace-gas chromatography/mass spectrometry (HS-GC/MS) to evaluate the level of volatile contaminant biodegradation. The effects of the following parameters were studied: temperature and time of equilibration. The biodegradation experiments were carried out with bacteria inoculation in mineral media in presence of volatile hydrocarbon compounds (toluene, p-xylene, nonane and naphthalene). Autoclaved inoculates were used as control and reference sample. The optimal headspace conditions were observed when the vials were heated at 80 degrees C for 20 min, the syringe at 81 degrees C and an injection volume of 0.4 mL was used. This methodology has the advantage of being relative free from matrix effects.