吹扫捕集和GC-MS测定水中26种挥发性有机物

用吹扫捕集和气相色谱―质谱联用技术对地表水中的26种挥发性有机污染物进行同时测定。实验结果在2.0～50.0μg/L范围内线性良好,相关系数均大于0.99,检出限在0.08～0.91μg/L范围内。方法的平均回收率为87.33%～116.68%,相对标准偏差(RSD)均小于5%。该方法前处理简单快速,采用内标法定量准确度高,重复性好,适用于清洁水中挥发性有机物的测定。     

Determination of volatile priority pollutants in water by purge and trap and capillary column gas chromatography/mass spectrometry

Two wide-bore capillary columns are evaluated for their applicability to the purge-and-trap technique and GC/MS analysis of 34 volatile organics. Neither column is able to completely resolve all 34 compounds, as is also typical of the packed column; however, the analysis is faster than with the packed column (18 to 21 min compared to 30 min), and the column effluent is introduced directly into the mass spectrometer without requiring an open-split interface. Method precision, as assessed from the instrument response at a concentration of 50 micrograms/L per component, is better than +/- 5% for 41% of the compounds using the VOCOL column (diphenyl dimethyl polysiloxane with crosslinking moieties) and for 53% of the compounds using the 007 column (95% methyl 5% phenyl silicone). The instrument response is linear from 20 to 200 micrograms/L for most compounds, and the amounts loaded to either column without serious distortion of the peak shape or resolution can be as high as 5 micrograms per component. Because the VOCOL column resolved more compounds than the 007 column within approximately the same analysis time, this column is further tested for performance with groundwater samples.     

Ultratrace determination of 1,2,4-trichlorobenzene in waste water by purge and trap/gas chromatography coupled to different detectors: Flame ionization (FID), electron capture (ECD), and multiple ion detection-mass spectrometry (MID-MS)

High resolution gas chromatography (HRGC) coupled to a “purge and trap” extraction-injection technique is described as a method of determining 1,2,4-trichlorobenzene in water at levels as low as parts-per-trillion (ppt). In order to investigate the interference from other volatile organic compounds (VOCs) several detection systems were compared: flame ionization, electron capture, and mass spectrometry-multiple ion detection. Concentrations ranging from 15 to 600 ng/L were analyzed in 20 ml standard aqueous solutions. The mean accuracy of the method varied from 89 to 103%, and its mean precision varied from ± 0.85 to ± 7.5 % for all detectors. The detection limits were 20 ng/L for FID, 2 ng/L for ECD and 0.5 ng/L for MID-MS detectors. The procedure was successfully applied to the analysis of industrial waste waters. The necessity of an appropriate internal standard to improve the quantitative determination and to determine possible losses or degradation of 1,2,4-trichlorobenzene during handling or storage is discussed.     

Low‐temperature headspace‐trap gas chromatography with mass spectrometry for the determination of trace volatile compounds from the fruit of Lycium barbarum L.

The total saccharides content of Lycium barbarum L. is very high, and a high temperature would result in saccharide decomposition and the emergence of a large amount of water. Moreover, the volatile compounds from the fruit of L. barbarum L. are rather low in concentration. Hence, it is difficult for a conventional headspace method to study the volatile compounds from the fruit of L. barbarum L. Since headspace‐trap gas chromatography with mass spectrometry is an excellent method for trace analysis, a headspace‐trap gas chromatography with mass spectrometry method based on low‐temperature (30°C) enrichment and multiple headspace extraction was developed to explore the volatile compounds from the fruit of L. barbarum L. The headspace of the sample was extracted in 17 cycles at 30°C. Each time, the compounds extracted were concentrated in the trap (Tenax TA and Tenax GR, 1:1). Finally, all the volatile compounds were delivered into the gas chromatograph after thermal desorption. With the method described above, a total of 57 compounds were identified. The identification was completed by mass spectral search, retention index, and accurate mass measurement.     

Construction of an automated gas chromatography/mass spectrometry system for the analysis of ambient volatile organic compounds with on-line internal standard calibration

An automated sampling and enrichment apparatus coupled with a gas chromatography/mass spectrometry (GC/MS) technique was constructed for the analysis of ambient volatile organic compounds (VOCs). A sorbent trap was built within the system to perform on-line enrichment and thermal desorption of VOCs onto GC/MS. In order to improve analytical precision, calibration accuracy, and to safe-guard the long-term stability of this system, a mechanism to allow on-line internal standard (I.S.) addition to the air sample stream was configured within the sampling and enrichment apparatus. A sub-ppm (v/v) level standard gas mixture containing 1,4-fluorobenzene, chloropentafluorobenzene, 1-bromo-4-fluorobenzene was prepared from their pure forms. A minute amount of this I.S. gas was volumetrically mixed into the sample stream at the time of on-line enrichment of the air sample to compensate for measurement uncertainties. To assess the performance of this VOC GC/MS system, a gas mixture containing numerous VOCs at sub-ppb (v/v) level served as the ambient air sample. Various internal standard methods based on total ion count (TIC) and selective ion monitoring (SIM) modes were attempted to assess the improvement in analytical precision and accuracy. Precision was improved from 7-8% RSD without I.S. to 2-3% with I.S. for the 14 target VOCs. Uncertainties in the calibration curves were also improved with the adoption of I.S. by reducing the relative standard deviation of the slope (Sm%) by an average a factor of 4, and intercept (Sb%) by a factor of 2 for the 14 target VOCs.     

气相色谱法直接进样测定饮用水中挥发性卤代烃

 利用大口径毛细管柱气相色谱/电子捕获检测器(GC/ECD)方法,直接进样测定了饮用水中的三氯甲烷、四氯化碳、一溴二氯甲烷、二溴一氯甲烷、三溴甲烷等5种挥发性卤代烃。所建立的方法简便、快速、灵敏度高,并具有较好的精密度与准确度。当5种卤代烃化合物的质量浓度平均值为9.03～20.19μg/L时,CV为2.9%～7.5%,标准差为0.3～0.9μg/L。样品的加标回收率为80%～118%,标准曲线的相关系数为0.998和0.999。ECD的温度为350℃时,其最低检测限在0.1～0.7μg/L范围内,均低于文献报道值 。     

家具白乳胶中苯系物含量测定

建立了气相色谱内标法测定家具白乳胶中苯系物含量的方法。样品中苯系物经甲醇提取、离心,上清液用60 m EN-20色谱柱分离,气相色谱检测,内标法定量。优化条件下苯系物回收率在96.84%~103.86%,相对标准偏差(RSD)为0.79%~2.28%,定量下限2.4~2.9 mg/L。方法操作简单,准确度和精密度较高,是一种检测白乳胶产品中苯系物含量的有效方法。     

Analysis of Trace Levels of Volatile Organic Contaminants in Municipal Drinking Water by Glass Capillary Gas Chromatography Using Simultaneous Flame Ionization and Electron Capture Detection

Abstract

A glass capillary gas chromatographic system using simultaneous flame ionization (FID) and electron capture (ECD) detection has been employed for the analysis of trace volatile organic pollutants in a municipal drinking water supply. The use of dual detectors with glass capillary columns allows resolution and detection of both halogenated and non-halogenated compounds simultaneously at less than microgram per liter (ppb) concentrations. By using diethyl ether as a solvent in preparing standard solutions of volatile organic compounds, standardization is made more accurate due to a reduction in solvent masking of early eluting peaks of interest. Additionally, ether shows promise for use in an internal standard method for quantification of VOA. These techniques were found to alleviate problems previously encountered in the analysis of purgeable organics and are described.     

High extraction efficiency fiber coated with calix[4] open-chain crown ether for solid-phase microextraction of polar aromatic and aliphatic compounds

The calix[4] open-chain crown ether, 5,11,17,23-tetra-tert-butyl-25,27-di(2-allyloxyethoxyl)-26,28-dihydroxycalix[4]arene was synthesized and used for preparation of solid-phase microextraction (SPME) fibers of enhanced extraction efficiency. The new SPME coating made from calix[4] open-chain crown ether and hydroxyl-terminated silicone oil was developed with the aid of vinyltriethoxylsilane as bridge using sol-gel method and cross-linking technology. The efficiency of the novel fiber in the extraction of polar aromatic and aliphatic compounds, such as phenols, alcohols, and volatile fatty acids, was also investigated. Due to the introduction of the polar open-chain crown ether in calix[4]arene molecules, the calix[4] open-chain crown ether fiber showed much better selectivity and sensitivity to these polar compounds in comparison with calix[4]arene fiber. It also had superior extraction efficiency when compared to commercial poly(dimethylsiloxane)-divinylbenzene and polyacrylate fibers. Parts per billion to parts per trillion level detection limits were achieved for most of the analytes through SPME in conjunction with GC and flame ionization detector. The linear ranges were two to four orders of magnitude, and the RSD values were below 7% for all analytes. The novel fiber was applied to determine volatile alcohols and fatty acids in wine samples. The volatile-free wine prepared in this work was used to assure similar chemical environment for analytes in both calibration solutions and in real wine samples, thus compensating for possible matrix interferences. The established internal standard method using 4-methyl-2-pentanol as internal standard showed satisfactory accuracy and precision.     

Determination of volatile compounds in cider spirits by gas chromatography with direct injection

Two analytical methods based on gas chromatography with direct injection are described for the quantitative analysis of volatile compounds (acetals, aldehydes, esters, alcohols, and volatile phenols) in cider brandies. Analytes were divided into major, 15, and minor volatile, 24, compounds depending on their usual concentration in samples. Parameters usually tested for method validation are evaluated. Correlation coefficients are calculated to estimate linearity, obtaining values higher than 0.999. Detection limits range between 0.325 mg/L (1-propanol) and 1.663 mg/L (methanol) among the major volatile compounds and between 0.086 mg/L (ethyl 2-methylbutyrate) and 0.332 mg/L (ethyl tetradecanoate) among the minor volatiles. Mean recoveries ranged between 109% (ethyl lactate) and 95% (1-butanol) for major volatiles and between 109% (1-octen-3-ol) and 94% (ethyl 2-methylbutyrate) for minor volatiles, thus confirming the accuracy of both methods. Reproducibility for major volatiles is < 5.4% (furfural) in all cases and < 9.6% (hexyl acetate) for minor volatiles. Moreover, the accuracy of the methods is evaluated by analyzing a certified whisky and five samples from interlaboratory assays, generally obtaining results in accordance with previous values.     

一种简易同时蒸馏萃取方法用于八角茴香挥发油提取及其GC-MS分析

设计了一种简易同时蒸馏萃取(SSDE)装置并用于八角茴香挥发油提取及其气相色谱-质谱法(GC-MS)分析。 该装置由圆底烧瓶、恒压滴液漏斗和回流冷凝管构成。 通过对八角茴香挥发油组分的GC-MS分析,比较SSDE法和水蒸汽蒸馏提取法(HD)提取植物源挥发油的效果。 结果表明,SSDE法所得挥发油相对含量在0.1%以上的19种化合物占挥发油总量的98.84%(相对标准偏差(RSD)(n=3)均不大于5.59%,其中RSD﹤5%的17种化合物占鉴定组分89.5%。SSDE法和HD法挥发油平均收率分别为7.30%(RSD=2.37%(n=5))和6.67%(RSD=5.26%(n=5))。 SSDE法简便、快速,适用于八角茴香挥发油的提取。     

Species-specific isotope-ratio measurements of volatile tin and antimony compounds using capillary GC-ICP-time-of-flight MS

The analytical performance of an axial inductively-coupled-plasma time-of-flight mass spectrometer (ICP-TOFMS) as a detector for fast transient chromatographic signals resulting from the coupling to capillary gas chromatography (CGC) was investigated. A cryotrapping GC-ICP-TOFMS method for the determination of volatile metal(loid) compounds (VOMs) in gases was used and the suitability of the TOF mass analyzer for multielemental speciation analysis and multi-isotope ratio determinations was studied in terms of accuracy and precision. Isotope ratios 118Sn/120Sn and 121Sb/123Sb have been determined in in-house gas standard atmospheres in Tedlar bags at two different levels (100 pg and 1 ng) for different elemental species (SnH4, MeSnH3, Me2SnH2, Me3SnH, BuSnH3, SbH3, and MeSbH2). A limitation arising from counting statistics in both detection modes could be shown. A solution containing rhodium (10 ng mL(-1)) and cadmium (40 ng mL(-1)) was introduced simultaneously to the GC outlet. Rhodium acts as a continuous internal standard and Cd is used for mass-bias correction (by measuring the 111Cd/113Cd ratio). The detection system in both pulse counting and analog mode was examined. The best attainable precision was established for Me2SnH2 (analog mode, 12 replicates, 1 ng, RSD 0.34%, accuracy 0.31%) whereas most other species ranged between 0.4 and 0.5% RSD if higher concentrations were used. The limitations of the pulse counting system are clearly seen, with peak heights of more than 2000 counts reaching saturation (for an integration time of 100 ms), which reduces the accuracy of isotope ratio determinations. A dozen VOM could be detected in an aged landfill gas sample; several unidentified Sn compounds were present. Although their isotope ratios are within the confidence value of the standards, it is not yet clear if the acquired precision is good enough to identify isotopic fractionation of metal(loid)s through biovolatilization processes. With the precision achieved, the combination of cryotrapping GC and ICP-TOFMS is a powerful tool for monitoring volatile multi-element species in multi-tracer experiments and isotope dilution methodology.     

Trace level analysis of volatile and semi-volatile organic compounds in water using a membrane/jet separator interfaced to an ion trap mass spectrometer

An ion trap mass spectrometer, equipped with a membrane/jet separator interface, is used for the direct detection of volatile and semi-volatile organic compounds in aqueous solutions. Aqueous sample is passed through a capillary membrane, the outside surface of which is continuously purged by helium. The permeate is pneumatically transported to the mass spectrometer via a jet separator which acts as an additional enrichment device. The performance and response characteristics of non-porous silicone and microporous polytetrafluoroethylene (PTFE) membranes are studied. The microporous membrane allows sufficient water to pass for it to be used as a reagent gas for chemical ionization. Both types of membranes provide detection limits in the parts per trillion (pptr) to parts per billion (ppb) range with a linear dynamic range of 3 orders of magnitude for some volatile organic compounds. Results show that there is no detectable matrix effect on response in the selected cases examined. The use of microporous membranes to analyze more polar compounds, such as 5-hydroxymethyl furfuraldehyde and lactic acid, is also demonstrated. The effects of other experimental parameters, such as membrane temperature and length, on sensitivity are also investigated.     

气相色谱法测定污水处理产生的氧 亚氮的分析方法研究

建立了气相色谱法(GC/ECD)检测污水处理过程中产生的温室气体氧化亚氮(N2O)的分析方法.确定了最佳实验条件:进样口温度、柱温和ECD检测器温度分别为105、100、300℃,以95％ Ar +5％ CH4为载气,柱流速和尾吹气流速分别为25、50 mL/min.N2O的质量浓度在0.255～ 100 mg/L范围...     

Trace-level determination of 1,4-dioxane in water by isotopic dilution GC and GC-MS

The volatile and polar solvent 1,4-dioxane has recently been reported as a contaminant of ground and surface waters, establishing the need to determine this substance in drinking water. This investigation established that 1,4-dioxane can be determined in water by various techniques including direct aqueous injection (DAI) gas chromatography (GC) and purge and trap GC-mass spectrometry (MS). Purge and trap GC-MS is limited by 1,4-dioxane's poor purge efficiency, resulting in detection limits up to 100 times greater than the efficiently purged volatile organic compounds. To attain the sensitivity required for drinking water monitoring, a method based on continuous liquid-liquid extraction with dichloromethane was developed. Isotope dilution was more accurate and reproducible than quantification with external standards, and the improvement in precision led to a lower method detection limit, 0.2 microgram L-1, using a quadrupole ion trap instrument in the electron ionization mode. Isotope dilution accuracy approached 100% in ppb determinations. Isotopic dilution quantification was also possible using a non-selective GC detector owing to the high efficiency of capillary GC columns that resolve the deuterium-labeled solvent from the natural isotopes.     

气相色谱-质谱联用法测定腌制水产品中的挥发性N-亚硝胺类化合物

建立了气相色谱-质谱(GC-MS)快速测定腌制水产品中挥发性N-亚硝胺含量的分析方法。采用GC-MS测定了N-二甲基亚硝胺(NDMA)、N-二乙基亚硝胺(NDEA)、N-二丙基亚硝胺(NDPA)、N-亚硝基吡咯烷(NPYR)、N-亚硝基哌啶(NPIP)、N-二丁基亚硝胺(NDBA)6种化合物,考察了样品不同提取方法、不同固相萃取小柱、不同色谱柱对分离检测的影响。结果显示: 在10～1000 μg/L范围内,线性相关系数可达0.9998以上;重现性良好,相对标准偏差小于8%;回收率可达79%～105%;灵敏度高,检出限低,除NDPA为0.03 μg/kg外,其他5种N-亚硝胺为0.05 μg/kg。该方法前处理快速简捷,易于操作,适用于腌制水产品中N-亚硝胺残留量的检测工作。     

Simultaneous determination of eight common odors in natural water body using automatic purge and trap coupled to gas chromatography with mass spectrometry

Production and fate of taste and odor (T&O) compounds in natural waters are a pressing environmental issue. Simultaneous determination of these complex compounds (covering a wide range of boiling points) has been difficult. A simple and sensitive method for the determination of eight malodors products of cyanobacterial blooms was developed using automatic purge and trap (P&T) coupled with gas chromatography-mass spectrometry (GC-MS). This extraction and concentration technique is solvent-free. Dimethylsulfide (DMS), dimethyltrisulfide (DMTS), 2-isopropyl-3-methoxypyrazine (IPMP), 2-isobutyl-3-methoxypyrazine (IBMP), 2-methylisoborneol (MIB), β-cyclocitral, geosmin (GSM) and β-ionone were separated within 15.3 min. P&T uses trap #07 and high-purity nitrogen purge gas. The calibration curves of the eight odors show good linearity in the range of 1-500 ng/L with a correlation coefficient above 0.999 (levels=8) and with residuals ranging from approximately 83% to 124%. The limits of detection (LOD) (S/N=3) are all below 1.5 ng/L that of GSM is even lower at 0.08 ng/L. The relative standard deviations (RSD) are between 3.38% and 8.59% (n=5) and recoveries of the analytes from water samples of a eutrophic lake are between 80.54% and 114.91%. This method could be widely employed for monitoring these eight odors in natural waters.     

自制炭阱吸附装置与气相色谱-质谱联用测定植物的挥发性有机物

设计组装了炭阱吸附装置,并与气相色谱-质谱(GC-MS)联用测定了银杏叶和利马豆的挥发性有机物。采用炭阱吸附装置与固相微萃取(SPME)收集银杏叶的挥发性有机物,用GC-MS进行分析,结果表明采用炭阱吸附装置对银杏叶挥发性有机物的富集效果优于SPME方法。实验还采用内标法对利马豆的挥发性有机物进行了初步的定量,两次实验结果的重复性较好。由于炭阱吸附装置能够很好地收集植物的挥发性有机物,且可以进行多个样品的平行实验及植物挥发性有机物的定量研究,因此炭阱吸附装置与GC-MS联用更适合用于实验室中植物挥发性有机物的研究。     

Needle‐trap device for the sampling and determination of chlorinated volatile compounds

A needle‐trap device, with immobilized sorbent inside the syringe, coupled with GC–MS was applied for air sampling and determination of chlorinated volatile organic compounds such as dichloromethane, trichloromethane, and tetrachloromethane. The application of a needle trap packed with combination of three sorbents including Tenax TA, Carbopack X, and Carboxen 1000 resulted in detection limits of few pg for chlorinated volatile compounds and recoveries of 99.2–102.8%. The extraction and desorption parameters were optimized within the study. As a result, the precision determined as RSD was equal to 5.05 and 3.03 and 6.52% for dichloromethane, trichloromethane, and tetrachloromethane, respectively. The storage time for chlorinated compounds up to 48 h and reusability of the needle‐trap device were verified. The obtained results have proved the ability of needle traps to compete with other solventless sampling and sample preparation extraction techniques.     

A new approach to determine method detection limits for compound-specific isotope analysis of volatile organic compounds

Compound-specific isotope analysis (CSIA) has been established as a useful tool in the field of environmental science, in particular in the assessment of contaminated sites. What limits the use of gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is the low sensitivity of the method compared with GC/MS analysis; however, the development of suitable extraction and enrichment techniques for important groundwater contaminants will extend the fields of application for GC/IRMS. So far, purge and trap (P&T) is the most effective, known preconcentration technique for on-line CSIA with the lowest reported method detection limits (MDLs in the low microg/L range). With the goal of improving the sensitivity of a fully automated GC/IRMS analysis method, a commercially available P&T system was modified. The method was evaluated for ten monoaromatic compounds (benzene, toluene, para-xylene, ethylbenzene, propylbenzene, isopropylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, fluorobenzene) and ten halogenated volatile organic compounds (VOCs) (dichloromethane, cis-1,2-dichloroethene, trans-1,2-dichloroethene, carbon tetrachloride, chloroform, 1,2-dichloroethane, trichloroethene, tetrachlorethene, 1,2-dibromoethane, bromoform). The influence of method parameters, including purge gas flow rates and purge times, on delta13C values of target compounds was evaluated. The P&T method showed good reproducibility, high linearity and small isotopic fractionation. MDLs were determined by consecutive calculation of the delta13C mean values. The last concentration for which the delta13C value was within this iterative interval and for which the standard deviation was lower than +/-0.5 per thousand for triplicate measurements was defined as the MDL. MDLs for monoaromatic compounds between 0.07 and 0.35 microg/L are the lowest values reported so far for continuous-flow isotope ratio measurements using an automated system. MDLs for halogenated hydrocarbons were between 0.76 and 27 microg/L. The environmental applicability of the P&T-GC/IRMS method in the low-microg/L range was demonstrated in a case study on groundwater samples from a former military air field contaminated with VOCs.