Multiple headspace solid-phase microextraction for the quantitative determination of volatile organic compounds in multilayer packagings

The theory of multiple headspace solid-phase microextraction (HS-SPME) and a method based on multiple HS-SPME for the quantitative determination of volatile organic compounds (VOCs) in packaging materials is presented. The method allows the direct analysis of solid samples without using organic solvents to extract analytes. Multiple headspace solid-phase microextraction is a stepwise method proposed to eliminate the influence of the sample matrix on the quantitative analysis of solid samples by HS-SPME. Different amounts of packaging and different volumes of standard solution were studied in order to remove a substantial quantity of analytes from the headspace at each extraction and obtain the theoretical exponential decay of the peak area of the four successive extractions and, thus, the total area was calculated from these four extractions. In addition, two fibres were compared: carboxen-polydimethylsiloxane (CAR-PDMS) and divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS), as they showed differences in the linearity of the exponential decay with the number of extractions depending on the compound. The CAR-PDMS fibre was better for the VOCs with a low molecular mass, whereas the DVB-CAR-PDMS fibre was better for the VOCs with a high molecular mass. Finally, the method was characterised in terms of linearity, detection limit and reproducibility and applied to analyse four multilayer packaging samples with different VOCs contents.     

Evaluation of multiple solid-phase microextraction as a technique to remove the matrix effect in packaging analysis for determination of volatile organic compounds

Multiple solid-phase microextraction (SPME) is an useful technique for the direct quantification of solid samples removing any matrix effect. The volatile organic compounds formed in the extrusion-coating process of multilayer packaging materials have already been quantified by multiple HS-SPME coupled to gas chromatography (GC)-mass spectrometry (MS) using volatile organic compound (VOC) solutions in hexadecane for calibration. In this article, water is proposed as solvent to prepare the calibration solutions because it provides a shorter calibration time, better linearity, better reproducibility, and lower detection limits than hexadecane. Besides, the extraction of VOCs from aqueous solutions is exhaustive and avoids the extrapolations needed to calculate the total peak areas, as they can be calculated as the sum of the individual areas of each extraction. Finally, it is checked whether the two solvents provide the same mean values for the total peak areas.     

Direct quantitation of volatile organic compounds in packaging materials by headspace solid-phase microextraction-gas chromatography-mass spectrometry

The quantification of volatile organic compounds (VOCs) in flexible multilayer packaging materials using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was studied. The analytes imclude 22 compounds such as aldehydes. ketones, carboxylic acids and hydrocarbons formed by thermooxidative degradation of polyethylene during the extrusion coating process in the manufacture of the packaging, and many of them are involved in the unpleasant and undesirable odour of these materials. External standard calibration using a solution of the analytes in an appropriate solvent was the first approach studied. Aqueous solutions of the analytes provided low reproducibility and the reduction of aldehydes to alcohols under the HS-SPME conditions. Hexadecane was chosen as the solvent since its polarity is similar to that of polyethylene and its volatility is lower than that of the analytes. However, hexadecane should be added to the sample before the analysis as it modifies the absorption capacity of the fibre. A 75-microm Carboxen-poly(dimethylsiloxane) fibre was used to extract the VOCs from the headspace above the packaging in a 15-ml sealed vial at 100 degrees C after 5 min of preincubation. The influence of the extraction time on the amount extracted was studied for a standard solution of the analytes in hexadecane, together with the influence of the volume of the standard solution and the amount of the sample placed in the vial. Standard addition and multiple HS-SPME were also studied as calibration methods and the results obtained in the quantitative analysis of a packaging material were compared.     

Determination of volatile organic compounds in recycled polyethylene terephthalate and high-density polyethylene by headspace solid phase microextraction gas chromatography mass spectrometry to evaluate the efficiency of recycling processes

A method for the determination of volatile organic compounds (VOCs) in recycled polyethylene terephthalate and high-density polyethylene using headspace sampling by solid-phase microextraction and gas chromatography coupled to mass spectrometry detection is presented. This method was used to evaluate the efficiency of cleaning processes for VOC removal from recycled PET. In addition, the method was also employed to evaluate the level of VOC contamination in multilayer packaging material containing recycled HDPE material. The optimisation of the extraction procedure for volatile compounds was performed and the best extraction conditions were found using a 75 μm carboxen-polydimethylsiloxane (CAR-PDMS) fibre for 20 min at 60 °C. The validation parameters for the established method were linear range, linearity, sensitivity, precision (repeatability), accuracy (recovery) and detection and quantification limits. The results indicated that the method could easily be used in quality control for the production of recycled PET and HDPE.     

液态乳制品包装材料中VOCs迁移安全性研究

利用顶空/气相色谱-质谱(HS/GC-MS)联用法对百利包、利乐包、塑杯3种乳制品包装材料中的挥发性有机物(VOCs)进行迁移安全性研究。结果表明,平衡温度与保温时间对包装中的VOCs有不同程度的影响。百利包中均含有苯,部分含有异丙醇、乙苯、间/对二甲苯、邻二甲苯,包装材料中VOCs含量为85.64~102.10 ng/cm2;利乐包含有苯、间/对二甲苯、邻二甲苯,部分含有异丙醇、乙酸乙酯、乙酸丁酯、乙苯,包装材料中VOCs含量为54.77~75.16 ng/cm2;塑杯均含有苯,部分含有异丙醇、间/对二甲苯、邻二甲苯,包装材料中VOCs含量为82.63~171.25 ng/cm2。利用迁移模型对乳制品进行研究,得出苯迁移最坏情况为0.885×10-3mg/kg;穿过0.015 cm厚度包装材料所需的时间为76 d,大于其保质期45 d。     

Development of a screening method to determine the pattern of fermentation metabolites in faecal samples using on-line purge-and-trap gas chromatographic–mass spectrometric analysis

An on-line screening method to analyse volatile organic compounds (VOCs) in faecal samples was developed. VOCs were isolated from a standard solution or faecal samples using a purge-and-trap system and identified and quantified by GC–MS. The experimental conditions were optimised and the performance of the system was evaluated. Linear calibration curves were obtained with correlation coefficients of at least 0.992. RSDs within and between days were less than 10%. The method was successfully applied to the analysis of faecal samples, yielding 135 different volatile organic compounds identified in 11 faecal samples. Of those, 22 VOCs were found in all volunteers, whereas 34 VOCs were person-specific.     

顶空气相色谱-质谱法测定涂料中的5种挥发性有机物

建立了涂料中5种挥发性有机物(VOCs)的顶空气相色谱-质谱(HS/GC-MS)分析方法.对溶剂、平衡温度、平衡时间、GC-MS的分离检测等实验条件进行了优化.涂料样品经N,N-二甲基甲酰胺(DMF)-水(1 :1,体积比)溶解分散,经90 ℃、90 min静态顶空后,通过DB-VRX色谱柱分离和质谱检测,外标法定量....     

Determination of volatile organic compounds in water using ultrasound-assisted emulsification microextraction followed by gas chromatography

Volatile organic compounds (VOCs) are toxic compounds in the air, water and land. In the proposed method, ultrasound-assisted emulsification microextraction (USAEME) combined with gas chromatography-mass spectrometry (GC-MS) has been developed for the extraction and determination of eight VOCs in water samples. The influence of each experimental parameter of this method (the type of extraction solvent, volume of extraction solvent, salt addition, sonication time and extraction temperature) was optimized. The procedure for USAEME was as follows: 15 μL of 1-bromooctane was used as the extraction solvent; 10 mL sample solution in a centrifuge tube with a cover was then placed in an ultrasonic water bath for 3 min. After centrifugation, 2 μL of the settled 1-bromooctane extract was injected into the GC-MS for further analysis. The optimized results indicated that the linear range is 0.1-100.0 μg/L and the limits of detection (LODs) are 0.033-0.092 μg/L for the eight analytes. The relative standard deviations (RSD), enrichment factors (EFs) and relative recoveries (RR) of the method when used on lake water samples were 2.8-9.5, 96-284 and 83-110%. The performance of the proposed method was gauged by analyzing samples of tap water, lake water and river water samples.     

Static headspace analysis of volatile organic compounds in soil and vegetation samples for site characterization

Traditional methodologies for the characterization of volatile organic compounds (VOCs) in subsurface soil are expensive, time-consuming processes that are often conducted on samples collected at random. The determination of VOCs in near-surface soils and vegetation is the foundation for a more efficient sampling strategy to characterize subsurface soil and improve understanding of environmental problems.In the absence of a standard methodology for the determination of VOCs in vegetation and in view of the high detection limits of the method for soils, we developed a methodology using headspace gas chromatography with an electron capture detector for the determination of low levels (parts-per-billion to parts-per-trillion) of VOCs in soils and vegetation. The technique demonstrates good sensitivity, good recoveries of internal standards and surrogate compounds, good performance, and minimal waste. A case study involving application of this technique as a first-step vadose-zone characterization methodology is presented.     

Development of a headspace solid-phase microextraction-gas chromatography-mass spectrometry method for the identification of odour-causing volatile compounds in packaging materials

A method for the identification of volatile organic compounds in packaging materials is presented in this study. These compounds are formed by thermooxidative degradation during the extrusion coating process in the manufacture of packaging. Headspace solid-phase microextraction (HS-SPME) was used as sample preparation technique prior to the determination of the volatile organic compounds by gas chromatography-mass spectrometry (GC-MS). The effects of extraction variables, such as the type of fibre, the incubation temperature, the pre-incubation time, the size of the vial and the extraction time on the amounts of the extracted volatile compounds were studied. The optimal conditions were found to be: carboxen-polydimethylsiloxane 75 microm fibre, 5 min of pre-incubation time, 100 degrees C of incubation temperature, 20-ml vial, and 15 min of extraction time. The chromatograms obtained by HS-SPME and static headspace extraction were compared in order to show that the HS-SPME method surpasses the static headspace method in terms of sensitivity. Twenty-five compounds were identified including carbonyl compounds (such as 3-methyl-butanal, 3-heptanone or octanal), carboxylic acids (such as pentanoic acid or hexanoic acid) known as odour causing compounds and hydrocarbons (such as decane, undecane or dodecane). Finally, the method was applied to different packaging samples (one odour-unacceptable, two odour-acceptable, and three odourless samples) and to the raw materials in order to find out the odour-responsible volatile organic compounds and their source.     

Evaluation of a Continuous Composite Sampler for Volatile Organic Compounds in Water

Abstract

The high volatility and low water solubility of volatile organic compounds (VOCs), make the collection of representative samples difficult. The standard grab sampling method only gives information of that moment in time when the sample is taken. When the composition of VOCs is varying, continuous composite sampling will give a more representative sample. However, no thorough evaluation of its use for VOCs has been reported.

The use of an automatic continuous composite sampler for the analysis of VOCs in water was studied. The causes and magnitude of the VOCs losses during the sampling process were determined.

Adsorbent cartridges were used to trap the VOCs escaping from solution during the sampling process. Sorption phenomena occurring on the containers and/or tubings were also evaluated. Sorption losses were much more significant than volatilization losses.

The results indicate that a modified version of this sampler can be an alternative for the long term sampling of water for VOC analysis.     

Determination of volatile organic compounds in industrial wastewater plant air emissions by multi-sorbent adsorption and thermal desorption-gas chromatography-mass spectrometry

This paper describes the process of determining the presence of volatile organic compounds in air emissions from industrial wastewater treatment plants (WWTP). The analytical method, based on thermal desorption-gas chromatography-mass spectrometry, was developed to simultaneously determine of 99 volatile organic compounds (VOCs) in air samples. This method is rapid, environmentally-friendly (since no organic solvents are used to extract the analytes) and compatible with a large range of thermally stable polar and apolar compounds. The target VOCs were selected on the basis of their occurrence in real samples and their adverse effects on the environment and human health. To cover the wide range of target compounds, multisorbent tubes filled with Tenax TA and Carbograph 1TD were used. Method validation showed good repeatabilities, low detection limits, a high linear range and good recoveries. At a fixed sample volume of 600?mL no significant losses for any of the target compounds were found in the samples. Stability during storage indicated that samples must be keep refrigerated at 4°C and analysed within three days of collection. Real samples were taken from air emissions of an industrial wastewater treatment plant located in the Southern Industrial Area of Tarragona (Spain) with the aim of studying its contribution as a source of atmospheric VOCs. This WWTP collects wastewater from several chemical factories which produce isocyanates, polyurethanes, chlorinated organics and functional chemicals among other products. Samples from the collecting tank after the primary sedimentation showed higher VOC concentrations than samples from the secondary treatment tank. The most abundant VOCs found in these emissions are included in the USEPA List of Hazardous Air Pollutants. The highest values correspond to acrylonitrile (up to 1843?µg?m^?3) and styrene (up to 573.70?µg?m^?3). The levels of chloroform, 1,4-dioxane, ethylbenzene, 1,2,3-trimethylbenzene and 1,4-diethylbenzene were also high.     

Oral malodor,assessed by closed-loop,gas chromatography,and ion-trap technology

A method is described for the analysis of volatile organic compounds in saliva and tongue coating samples. The techniue is based on an off-line preconcentration step by means of a closed-loop trapping system followed by gas chromatography-ion trap detection. With the closed-loop technique, the volatile organic compounds(VOCs) are released from the matrix and trapped on an adsorbent without interference of water. The VOCs are released from the adsorbent into the gas chromatograph by thermdesorption. After separation, identification of the compounds is performed by ion trap technology. By this technique 82 compounds could be demonstrated in saliva and tongue coating samples. The technique is also used to demonstrate the formation of volatile bacterial fermentation compounds when a protein substrate is added to tongue coating samples. It is considered a very promising tool in further research on oral malodor.     

水性涂料中挥发性有机化合物的气相色谱-质谱法测定

建立了内墙涂料中24种挥发性有机化合物(VOCs)的GC-MS检测方法,重点研究了现有检测方法分离度差和回收率低的问题,采用无水硫酸钠净化、二氯甲烷超声和膜过滤提取体系,改善了各种化合物的回收率,特别是提高了二元醇类化合物的回收率,优化后的实验条件下,样品的加标回收率为70%~94%,相对标准偏差不大于6.8%,检出限为3.1~10.6 mg/L。在30~300 mg/L范围内,方法的线性关系良好,相关系数大于0.99。该方法简便、快速、灵敏、精密度好,完全满足进出口水性涂料中常见的24种挥发性有机化合物的检测要求。     

人体呼出气中挥发性有机化合物的检测方法

呼出气检测作为一种潜在的新型临床检测手段受到广泛关注。本文详细综述了人体呼出气中挥发性有机化合物(VOCs)的各类检测方法和技术,分别对色谱法、质谱法和光谱及传感器法的原理、特点和最新研究进展进行了介绍,对照总结了目前已确定的异戊二烯、丙酮等疾病生物标志物的各种分析方法和实测数据,并展望了未来的研究动向。     

Evaluation of multi-walled carbon nanotubes as an adsorbent for trapping volatile organic compounds from environmental samples

A type of purified multi-walled carbon nanotubes (PMWCNTs) prepared by catalytic decomposition of methane, with a surface area of 98 m2/g, was evaluated as an adsorbent used for tapping volatile organic compounds (VOCs). The performance in evaluation was based on breakthrough volumes (BTVs) and recoveries of selected VOCs. PMWCNTs were also used as a trap packing material to adsorb VOCs purged from spiked water sample. Due to their porous structure, PMWCNTs were found to have much higher BTVs than that of Carbopack B, a graphitized carbon black with the same surface area as PMWCNTs. The recoveries of the tested VOCs trapped on PMWCNTs ranged from 80 to 110%, and not affected by the humidity of purge gas. The results indicate that PMWCNTs are a potential useful adsorbent for direct trapping VOCs from air samples and may be a supplement to VOCARB 3000, a commercially available trap, in purge-and-trap system to preconcentrate VOCs from water samples.     

Determination of UV filters in packaging by focused ultrasonic solid-liquid extraction and liquid chromatography

A focused ultrasonic solid-liquid extraction (FUSLE) and high performance liquid chromatography (HPLC) with a diode array detector (DAD) is proposed for the determination of ten fat-soluble UV filters in packaging. FUSLE technique is relatively new and has been used for the extraction of a few analytes; such as polycyclic aromatic hydrocarbons and other organic pollutants. In this work, it has been demonstrated that FUSLE is a useful, fast and simple extraction methodology for UV filters because the complete extraction was carried out with just 6ml of tetrahydrofuran and in only one cycle of 30s. The developed method has been validated and applied to the analysis of polyethylene-based multilayer packaging samples. The FUSLE-based method allows the sensitive detection of most of the UV-filters in polyethylene, with limits of detection between 0.4 and 8.5ngmg(-1) (except for BDM). Intra and inter-day relative standard deviation values were below 5 and 14%, respectively, except for MBP. In addition, the proposed method was more efficient than tetrahydrofuran extraction under reflux for 2.5h for all the analytes except for EMT and BDM. Therefore, the developed method can be used to establish the absorption capability of different types of packaging and this information will be very useful in packaging selection.     

Novel sample preparation technique with needle-type micro-extraction device for volatile organic compounds in indoor air samples

A novel needle-type sample preparation device was developed for the effective preconcentration of volatile organic compounds (VOCs) in indoor air before gas chromatography–mass spectrometry (GC–MS) analysis. To develop a device for extracting a wide range of VOCs typically found in indoor air, several types of particulate sorbents were tested as the extraction medium in the needle-type extraction device. To determine the content of these VOCs, air samples were collected for 30 min with the packed sorbent(s) in the extraction needle, and the extracted VOCs were thermally desorbed in a GC injection port by the direct insertion of the needle. A double-bed sorbent consisting of a needle packed with divinylbenzene and activated carbon particles exhibited excellent extraction and desorption performance and adequate extraction capacity for all the investigated VOCs. The results also clearly demonstrated that the proposed sample preparation method is a more rapid, simpler extraction/desorption technique than traditional sample preparation methods.     

Quality control in quantification of volatile organic compounds analysed by thermal desorption-gas chromatography-mass spectrometry

This paper presents a detailed study on the calibration of a thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS)-based methodology for quantification of volatile organic compounds (VOCs) in gaseous and liquid samples. For the first time, it is documented to what extent three widely encountered problems affect precise and accurate quantification, and solutions to improve calibration are proposed. The first issue deals with the limited precision in MS quantification, as exemplified by high relative standard deviations (up to 40%, n=5) on response factors of a set of 69 selected VOCs in a volatility range from 16 Pa to 85 kPa at 298 K. The addition of [(2)H(8)]toluene as an internal standard, in gaseous or liquid phase, improves this imprecision by a factor of 5. Second, the matrix in which the standard is dissolved is shown to be highly important towards calibration. Quantification of gaseous VOCs loaded on a sorbent tube using response factors obtained with liquid standards results in systematic deviations of 40-80%. Relative response factors determined by the analysis of sorbent tubes loaded with both analytes and [(2)H(8)]toluene from liquid phase are shown to offer a reliable alternative for quantification of airborne VOCs, without need for expensive and often hardly available gaseous standards. Third, a strategy is proposed involving the determination of a relative response factor being representative for a group of analytes with similar functionalities and electron impact fragmentation patterns. This group method approach indicates to be useful (RSD approximately 10%) for quantifying analytes belonging to that class but having no standards available.     

Discriminant Analysis of Volatile Organic Compounds data related to a new location method of entrapped people in collapsed buildings of an earthquake

Discriminant Analysis is used as a part of a research, which aims at using expired air analysis for the early location of entrapped people under the ruins of collapsed buildings in an earthquake. This work focuses on the possibility of distinguishing Volatile Organic Compounds (VOCs) in the entrapment area which originate from different sources. Five categories of samples were analyzed by Thermal Desorption-Gas Chromatography-Mass Spectrometry (TD-GC-MS). Expired air samples from healthy humans (Category 1) and fasting people (Category 2) were analyzed for studying the VOCs attributed to entrapped people. Headspace air of urban waste disposal bins (Category 3), headspace air of bags with decaying human bodies (Category 4) and urban air samples (Category 5) were analyzed for studying the VOCs attributed to background sources. Discriminant Rotation, a specific type of Discriminant Analysis was applied on the VOCs concentration matrix of the five categories. Combinations of VOCs that best discriminated each category were determined. Cluster Analysis was used to validate the results of Discriminant Analysis. The advantages and limitations of the method are presented and discussed.