Performance evaluation of a sorbent tube sampling method using short path thermal desorption for volatile organic compounds

Air sampling, using sorbents, thermal desorption and gas chromatography, is a versatile method for identifying and quantifying trace levels of volatile organic compounds (VOCs). Thermal desorption can provide high sensitivity, appropropriate choices of sorbents and method parameters can accommodate a wide range of compounds and high humidity, and automated short-path systems can minimize artifacts, losses and carry-over effects. This study evaluates the performance of a short-path thermal desorption method for 77 VOCs using laboratory and field tests and a dual sorbent system (Tenax GR, Carbosieve SIII). Laboratory tests showed that the method requirements for ambient air sampling were easily achieved for most compounds, e.g., using the average and standard deviation across target compounds, blank emissions were < or = 0.3 ng per sorbent tube for all target compounds except benzene, toluene and phenol; the method detection limit was 0.05 +/- 0.08 ppb, reproducibility was 12 +/- 6%, linearity, as the relative standard deviation of relative response factors, was 16 +/- 9%, desorption efficiency was 99 +/- 28%, samples stored for 1-6 weeks had recoveries of 87 +/- 9%, and high humidity samples had recoveries of 102 +/- 12%. Due to sorbent, column and detector characteristics, performance was somewhat poorer for phenol groups, ketones, and nitrogen containing compounds. The laboratory results were confirmed in an analysis of replicate samples collected in two field studies that sampled ambient air along roadways and indoor air in a large office building. Replicates collected under field conditions demonstrated good agreement except for very low concentrations or large (> 41 volume) samples of high humidity air. Overall, the method provides excellent performance and satisfactory throughput for many applications.     

合肥市冬季细颗粒物中碳组分特征分析

利用2020年12月1日至2021年2月28日合肥市细颗粒物(PM_2.5)、有机碳(OC)和元素碳(EC)等环境空气质量监测数据和气象观测数据,分析了合肥市大气PM_2.5中OC和EC的污染特征,并探讨了其来源以及气象因素影响。结果表明：合肥市冬季碳质气溶胶是PM_2.5中主要组分,随着污染程度的加重,碳质气溶胶的质量浓度逐步增加,但其在PM_2.5中的占比先减小后增加。在以PM_2.5为首要污染物的不同污染级别天气条件下,OC和EC的相关性说明不同程度下碳质气溶胶来源复杂。OC/EC表明机动车尾气和燃煤源排放是碳质气溶胶的主要来源。二次有机碳(SOC)会随着污染程度的加重而呈现升高趋势。OC和EC在冬季受温度影响较小;较大的相对湿度对OC和EC具有一定的清除作用,明显降水或连续降水的清除作用更加显著;而风速对含碳气溶胶的影响主要出现在污染天气背景下。     

Workplace monitoring for volatile organic compounds using thermal desorption-gas chromatography-mass spectrometry

The interest in the identification of volatile organic compounds in the workplace has been a major focus of many National Institute for Occupational Safety and Health (NIOSH) field studies. A primary technique for sampling and analysis of these compounds is summarized by NIOSH Manual of Analytical Methods (NMAM) 2549. This is a screening method that uses a multi-bed sorbent to trap a wide variety of compounds and compound classes. Thermal desorption techniques are used as a first attempt to characterize potential contaminants in a workplace and to determine what future sampling and analyses must be performed. Field examples are provided to show the versatility of thermal desorption methods and techniques. Due to their sensitivity, thermal desorption tube methods are sometimes required in order to measure the workplace concentrations of unusual compounds. In other situations, the exposures are too high or varied to make thermal desorption tubes practical. In these cases, the identification of contaminants with thermal desorption tubes leads to new method developments for the quantification of specific compounds using more conventional solid sorbent-solvent desorption based methods.     

吹扫捕集-气相色谱/质谱法同时测定水中的27种挥发性有机物

水中的VOCs经吹扫富集、解吸后,用HP-VOC色谱柱分离,采用全扫描和选择离子监测模式分析,内标法定量。最佳富集条件为:吹扫流速为40 m L/min,吹扫温度为40℃,吹扫时间为15 min,解吸温度为200℃,解吸时间为2 min。该法27种VOCs在一定的质量浓度范围内与其峰面积呈线性关系,相关系数r0.995,检出限为0.02~1.18μg/L。以空白样品为基体进行加标回收试验,测得回收率为79.8%~114%,相对标准偏差为0.3%~12%。     

High Resolution GC - MS Analysis of VOCs in Wastewater and Sludge

High resolution gas chromatography - mass spectrometry (GC-MS) has been widely used in the field of environmental sample analysis for volatile organic compounds (VOCs) (Gryder-Boutet, et al., 1988). Such a technique was applied to the analysis of VOCs at a local municipal wastewater treatment plant. The combination of purge and trap sample preparation and thermal desorption with cryofocusing technology, allows for the detection of a wide range of volatiles in wastewater and sludge samples. Results show that a large variety of organics present in samples are aliphatic and aromatic hydrocarbons. Their concentrations are in part per billion levels between 10 to 150 g/L. Others identified using this method are chlorinated hydrocarbons, sulfides and organic acids. By comparing the chromatograms of different wastewater and sludge samples collected from various treatment process units, it can be seen that most volatiles were removed or degraded after the aeration or digestion process. Information that provides an insight to the measurement of organic compounds in sludges is also discussed in this paper.     

Effect of sample flow rate and sampling duration on the absorption of NO2 in the sodium arsenite monitoring method

The effect of the two most critical parameters, the sample flow rate and sampling duration, on the absorption efficiency of NO2 in the sodium arsenite method of nitrogen dioxide determination in ambient air was studied. Laboratory experiments showed a high sensitivity to these parameters, which were subjected to variation during actual field monitoring. The reported NO2 absorption efficiency of the method of 82% at a flow rate of 0.2 l min-1 was found to be as low as 33% at a flow rate of 1.0 l min-1 for a sampling duration of 24 h. Similarly, a considerable decrease in absorption efficiency with increasing sampling duration from 2 to 24 h was observed at a particular flow rate. Correction factors for the absorption efficiency were evolved that can be used to update the existing database, as well as future NO2 data generated using this manual monitoring method.     

土壤中挥发性有机物的顶空制备方法研究

对土壤中挥发性有机物（VOCs）有效提取的顶空（HS）前处理条件进行了研究。结果表明,在一定的气相色谱条件下,影响顶空装置对挥发性有机物提取水平的主要有顶空平衡时间、平衡温度、基准修正液的加入量等因素,在一定的HS—GC条件下,土壤中挥发性有机物的准确度可达80%。     

Soil-Water Partitioning and Desorption Hysteresis of Volatile Organic Compounds from a Louisiana Superfund Site Soil

The adsorption and desorption of three volatile organic compounds (1,2- dichloroethane, 1,1,2- trichloroethane and 1,1,2,2-tetrachloroethane) from a previously uncontaminated clayey soil sample from a Superfund site in North Baton Rouge,Louisiana was studied. In the linear range of the adsorption isotherm, the partition constants were not affected by the presence of the co-solutes. The adsorption isotherms over a wide concentration range on the soil followed the nonlinearFreundlich isotherm. The desorption of the compounds showedsignificant hysteresis at all concentrations studied. Approximately 20 to 70% of the adsorbed mass of organic compounds resisted the desorption even after five months ofsuccessive desorption steps. The desorption of four compounds(1,2-dichloroethane, 1,1,2-trichloroethane, 1,4-dichlorobenzeneand hexachlorobutadiene) from a contaminated soil sample fromthe same site was also studied. The aqueous concentration declined as the successive desorption steps progressed. For hexachlorobutediene the desorption can be visualized as occurring in two stages. The first stage involved a loosely bound or reversible fraction and the second stage involveda tightly bound or resistant fraction.     

TH_PKU-300B挥发性有机物快速在线监测系统常见故障及解决

针对TH_PKU-300B挥发性有机物快速在线监测系统运行中常见的FID谱图基线不稳定、丙烷峰展宽拖尾、高沸点组分响应下降、GC/MS一直停留在预运行状态、热解析过程中GC进样口压力报警、控制软件温度显示故障、采样体积达不到设定值等故障,分析其产生原因,并提出相应的解决办法和预防措施,同时对TH_PKU-300B系统运维工作提出相关建议。     

对TH_PKU-300B挥发性有机物快速在线监测系统的改进

针对现有TH_PKU-300B挥发性有机机物快速在线监测系统在测定含氧挥发性有机化合物(OVOCs)、含氮挥发性有机物(NVOCs)和高沸点挥发性有机物时存在灵敏度低、精密度差、线性响应较差、记忆效应明显等不足,根据其原理,对其GC-MS通道的部分气路进行改进。通过实验对比分析,证明改进后的仪器系统响应更加灵敏、线性拟合度更高、精密度及解析效率均显著提高,同时检出限也由改进前的体积分数0.1×10~(-9)~1.0×10~(-9)降低至0.02×10~(-9)~0.08×10~(-9),并解决了记忆效应问题。改进后的系统在OVOCs、NVOCs和高沸点挥发性有机物测定方面要优于原系统。     

“罐采样-实验室分析”测定环境空气中117种挥发性有机物要点分析

“罐采样-实验室分析”是当前测定环境空气中挥发性有机物的主流方法。结合已有资料,针对方法涉及的采样、样品运输与保存、分析测试等环节,考察了环境空气中挥发性有机物监测的主要影响因素。罐选择、清洁度、气密性、惰性化是样品保存的先决条件;采样流量控制器的气密性、流量校准等是保证监测准确的基本要素;温度变化对样品保存产生影响;标准气体的湿度、配置平衡时间、保存时间、配制准确性和内标气体的保存时间等会导致校准和溯源产生偏差。样品中的水分及二氧化碳是分析过程中影响监测结果准确性的干扰因素,实验室有机溶剂也会干扰分析的准确性。     

Determination of 16 polycyclic aromatic hydrocarbons in water using fluorinated polyaniline-based solid-phase microextraction coupled with gas chromatography

The study on the performance of a fluorinated polyaniline (PANI) as a fiber coating for solid-phase microextraction (SPME) had been reported and 16 polycyclic aromatic hydrocarbons (PAHs) were selected to evaluate the performance of this fiber. Various parameters including sample volume, extraction temperature, time of desorption and extraction, pH and ionic strength were investigated intensively. A direct comparison between PANI-SPME fiber and commercial fiber was conducted. The results showed that the PANI-SPME coating had high affinity towards target compounds and the proposed method was successfully applied for the detection of real samples: rainfall and Taihu Lake water collected from Southern China. The whole PANI-SPME-GC method offers acceptable accuracy, precision and sensitivity and low detection limits, which is applicable to monitor trace levels of PAHs in real water bodies.     

Ambient level volatile organic compound (VOC) monitoring using solid adsorbents--recent US EPA studies

Ambient air spiked with 1-10 ppbv concentrations of 41 toxic volatile organic compounds (VOCs) listed in US Environmental Protection Agency (EPA) Compendium Method TO-14A was monitored using solid sorbents for sample collection and a Varian Saturn 2000 ion trap mass spectrometer for analysis. The adsorbent was a combination of graphitic carbon and a Carboxen-type carbon molecular sieve. The method detection limits (MDLs) for 11 samples were typically 0.5 parts per billion by volume (ppbv) and lower except for bromomethane and chloromethane, both of which exhibited breakthrough. Thirty-day sample storage on the sorbents resulted in less than a 20% change for most compounds, and water management was required for humid samples to avoid major anomalous decreases in response during analyses. The adsorbent-based system, a system using canister-based monitoring, and a semi-continuous automated GC/MS (autoGC) monitoring system with a Tenax GR/Carbotrap B/Carbosieve S-III adsorbent preconcentrator were compared using spiked ozone concentrations as a variable. In this comparison, the target compounds included a number of n-aldehydes as well as those listed in TO-14A. The effects of ozone on the TO-14A compounds were relatively minor with the exception of negative artifacts noted for styrene and 1,1,2,2-tetrachloroethane. However, a small, systematic decrease in response was evident for a number of aromatic VOCs and 1,1,2,2-tetrachloroethane when ozone was increased from 50 to 300 ppbv. Method averages for multiple runs under the same conditions were typically within +0.25 ppbv of their mean for most compounds. For n-aldehydes, strong positive artifacts using the autoGC preconcentrator and strong negative artifacts for the canister-based and carbon sorbent approaches caused major disagreement among methods. These artifacts were mostly eliminated by using MnO2 ozone scrubbers, although loss of the n-aldehydes for all methods occurred after a single sample collection of 1 h duration, apparently due to the interaction of the n-aldehydes and products of the O3, MnO2 reaction on the scrubber.     

Comparison of 24 h averaged VOC monitoring results for residential indoor and outdoor air using Carbopack X-filled diffusive samplers and active sampling--a pilot study

Analytical results obtained by thermal desorption GC/MS for 24 h diffusive sampling of 11 volatile organic compounds (VOCs) are compared with results of time-averaged active sampling at a known constant flow rate. Air samples were collected with co-located duplicate diffusive sampling tubes and one passivated canister. A total of eight multiple-component sampling events took place at fixed positions inside and outside three private homes. Subsequently, a known amount of sample air was transferred from the canister to an adsorbent tube for analysis by thermal desorption GC/MS. Results for the 11 most prevalent compounds--Freon 11, 1,3-butadiene, benzene, toluene, tetrachloroethene, ethylbenzene, m,p-xylene, o-xylene, 4-ethyltoluene, 1,3,5-trimethylbenzene, and p-dichlorobenzene--show that the ratio of average study values (diffusive sampling to active sampling) is 0.92 with 0.70 and 1.14 extreme ratios. Absolute percent difference for duplicate samples using diffusive sampling was <10% for the four most prevalent compounds. Agreement between the two sampling approaches indicates that the prediction of approximately constant diffusive sampling rates based on previous laboratory studies is valid under the field conditions.     

气相色谱法测定苯酚生产废水中芳香族化合物

建立了用气相色谱法同时测定苯酚生产废水中异丙苯、α-甲基苯乙烯、α-甲基苯甲醇、2-苯基-2-丙醇、苯酚、苯乙酮、2-苯基丙醛等7种芳香族有毒有机污染物的定量分析方法。采用二氯甲烷对水样进行萃取后进行分析测定,气相色谱条件:DB-WAX型色谱柱,FID检测器,程序升温,进样量1μL。方法的检出限、精密度、回收率实验表明,该方法对苯酚生产废水中各污染物组分具有较好的分离效果,对7种物质的检测限均低于0.05 mg/L,5次测定的相对标准偏差小于5%,实际水样的加标回收率大于97%。     

Airborne particulate-associated polyaromatic hydrocarbons,n-alkanes,elemental and organic carbon in three European cities

Total suspended particulate (TSP) samples were collected weekly over a period of one year at four European sites during 1995/6. Two sites were in London-a Central London site (CL, St Paul's Cathedral) and a suburban North London site (NL, Bounds Green); the other two sites were in Porto, Portugal and Vienna, Austria. TSP was collected using a low volume sampler. Organic carbon (OC) and elemental carbon (EC) concentrations were measured using a thermal-optical carbon analyser. Parallel samplers collected TSP for subsequent GC-MS analysis of thirty-nine combustion-associated organic compounds; 16 polyaromatic hydrocarbons (PAHs) and 23 n-alkanes. OC and EC correlate well at all sites (r2 = 0.39-0.65), although the London inter-site correlations were low, suggesting that local sources of OC and EC have a significant influence on local concentrations. Concentrations do not vary widely across the four urban sites, despite the significant differences in urban characteristics. Seasonal patterns of OC:EC ratios were similar at the London and Vienna sites, with highest ratios in autumn and winter, and annual mean OC:EC ratios were identical at these sites. The Carbon Preference Index (CPI) indicated vehicle emissions to have a stronger influence over particulate concentrations at the Vienna and central London sites; there was a stronger biogenic signature in north London and Porto. In addition, two PAH compounds (pyrene and fluoranthene) previously associated with diesel exhaust, were correlated with OC and EC concentrations at the London and Vienna sites.     

Background concentrations of individual and total volatile organic compounds in residential indoor air of Schleswig-Holstein, Germany

During a monitoring campaign concentrations of volatile organic compounds (VOCs) were measured in indoor air of 79 dwellings where occupants had not complained about health problems or unpleasant odour. Parameters monitored were the individual concentration of 68 VOCs and the total concentration of all VOCs inside the room. VOCs adsorbed by Tenax TA were then analysed by means of thermal desorption, gas chromatography and mass spectrometry. The analytical procedure and quantification was done according to the recommendation of the ECA-IAQ Working Group 13 which gave a definition of the total volatile organic compound (TVOC) concentration. Using this recommendation TVOC-concentrations ranged between 33 and 1600 microg m(-3) with a median of 289 microg m(-3). Compounds found in every sample and with the highest concentrations were 2-propanol, alpha-pinene and toluene. Save for a few samples, all concentrations measured have been a factor 2 to 10 lower, compared to data from similar studies. Only a few terpenes and aldehydes were found exceeding published reference data or odour threshold concentrations. However, it has been found that sampling and analysing methods do have a considerable impact on the results, making direct comparisons of studies somewhat questionable. 47% of all samples revealed concentrations exceeding the threshold value of 300 microg TVOC m(-3) set by the German Federal Environmental Agency as a target for indoor air quality. Using the TVOC concentration as defined in the ECA-IAQ methodology is instrumental in assessing exposure to VOCs and identifying sources of VOCs. The background concentrations determined in this study can be used to discuss and interpret target values for individual and total volatile organic compounds in indoor air.     

固相微萃取-气相色谱在水中有机污染物测定中的应用

固相微萃取技术是一种新型的无溶剂的样品前处理方法,集取样、萃取、富集、进样于一体,具有无溶剂、可直接进样、操作简便快捷、灵敏的特点。简述了固相微萃取技术原理,综述了SPME与GC联用在水中有机污染物测定中的应用。具体介绍了该技术在苯系物、酚类化合物、多环芳烃、有机氯化物及其它有机污染物分析中的应用,并提出了该技术的发展趋势及应用展望。     

Volatile Organic Compounds: Sampling Methods and Their Worldwide Profile in Ambient Air

The atmosphere is a particularly difficult analytical system because of the very low levels of substances to be analysed, sharp variations in pollutant levels with time and location, differences in wind, temperature and humidity. This makes the selection of an efficient sampling technique for air analysis a key step to reliable results. Generally, methods for volatile organic compounds sampling include collection of the whole air or preconcentration of samples on adsorbents. All the methods vary from each other according to the sampling technique, type of sorbent, method of extraction and identification technique. In this review paper we discuss various important aspects for sampling of volatile organic compounds by the widely used and advanced sampling methods. Characteristics of various adsorbents used for VOCs sampling are also described. Furthermore, this paper makes an effort to comprehensively review the concentration levels of volatile organic compounds along with the methodology used for analysis, in major cities of the world.     

深圳市宝安区环境空气有机污染现状研究

采用热脱附和气相色谱-质谱联用技术研究了深圳市宝安区环境空气中挥发性有机物的组成,从中鉴定出18种有机化合物,并通过对其中5种苯系物的定量分析结果,讨论了宝安区环境空气有机污染状况。