Passive sampling and analyses of common dissolved fixed gases in groundwater

An in situ passive sampling and gas chromatographic protocol was developed for analysis of the major and several minor fixed gases (He, Ne, H2, N2, O2, CO, CH4, CO2, and N2O) in groundwater. Using argon carrier gas, a HayeSep DB porous polymer phase, and sequential thermal conductivity and reductive gas detectors, the protocol achieved sufficient separation and sensitivity to measure the mixing ratio of all these gases in a single 0.5 mL gas sample collected in situ, stored, transported, and injected using a gastight syringe. Within 4 days of immersion in groundwater, the simple passive in situ sampler, whether initially filled with He or air, attained an equivalent and constant mixing ratio for five of the seven detected gases. The abundant mixing ratio of N2O, averaging 2.6%, indicated that significant denitrification is likely ongoing within groundwater contaminated with uranium, acidity, nitrate, and organic carbon from a group of four closed radioactive wastewater seepage ponds at the Oak Ridge Field Research Center. Over 1000 passive gas samples from 12 monitoring wells averaged 56% CO2, 32.4% N2, 2.6% O2, 2.6% N2O, 0.21% CH4, 0.093% H2, and 0.025% CO with an average recovery of 95 +/- 14% of the injected gas volume.     

Integrated sampling and analytical approach for common groundwater dissolved gases

A novel passive gas diffusion sampler (PGDS) combines sampling, storage and direct injection into a single gas chromatograph (GC). The sampler has a 4.5 mL internal volume when deployed, is easy to operate, and eliminates sample-partitioning. The associated GC method analyzes for a large, dynamic sampling range from a single, small volume injection. Dissolved gases were separated on parallel Rt-Molsieve 5A and Rt-Q-PLOT columns and eluted solutes were quantified using a pulse discharge helium ionization detector (PD-HID). The combined sampling and analytical method appears to be less prone to systematic bias than conventional sampling and headspace partitioning and analysis. Total dissolved gas pressure used in tandem with the PGDS improved the accuracy of dissolved gas concentrations. The incorporation of routine measurements of dissolved biogeochemical and permanent gases into groundwater investigations will provide increased insight into chemical and biological processes in groundwater and improve chemical mass balance accuracy.     

A New Analytical Method to Volatile Compounds in Cider Apples: Application to Evaluate the Starch Index

Headspace solid-phase microextraction coupled to Fast gas chromatography (GC) with flame ionization detector and with quadrupole mass spectrometric detector was employed to study the volatile compounds in Asturian cider apples. The best conditions used for volatile analysis of apple were: sample equilibration at 25 °C for 60 min, followed by polydimethylsiloxane-divinylbenzene fiber exposure to the headspace above the sample for 5 min, and finally thermal desorption of the adsorbed substances in the injector port for GC analysis. The use of Fast gas chromatography allowed the separation of 24 compounds in less than 8 min, reducing the analysis time in 80% compared with conventional gas chromatography. The aromatic profile of 26 crushed apple samples included in Designation of Origin Cider from Asturias was analyzed. The chemometric technique named multiple linear regression allowed us to establish a relationship between apple volatile compounds and the starch index. The results obtained are consistent with the known apple ripening model.     

Pumping-induced ebullition: a unified and simplified method for measuring multiple dissolved gases

The incorporation of multiple dissolved gas measurements in biogeochemical studies remains a difficult and expensive challenge. Incompatibilities in collection, handling, and storage procedures generally force the application of multiple sampling procedures for multiple gases. This paper introduces the concept and application of pumping-induced ebullition (PIE), a unified approach for routine measurement of multiple dissolved gases in natural waters and establishes a new platform for development of in situ real-time dissolved gas monitoring tools. Ebullition (spontaneous formation of bubbles) is induced by pumping a water sample through a narrow-diametertube (a "restrictor") to decrease hydrostatic pressure (PH) below total dissolved gas pressure (PT). Buoyancy is used to trap bubbles within a collection tower where gas accumulates rapidly (1 mL/min) to support multiple chemical analyses. Providing for field collection of an essentially unlimited and unified volume of gas sample, PIE afforded accurate and precise measurements of major (N2, 02, Ar), trace (CO2, N20, CH4) and ultratrace (CFC11, CFC12, CFC113, SF6) dissolved gases in Wisconsin groundwater, revealing interrelationships between denitrification, apparent recharge age-dates, and historical land use. Compared to conventional approaches, PIE eliminates multiple gas-specific sampling methods, reduces data computations, simplifies laboratory instrumentation, and avoids aqueous production and consumption of biogenic gases during sample storage. A lake depth profile for CO2 demonstrates PIE's flexibility as an in situ real-time platform for dissolved gas measurements. The apparent departures of some gases (SF6, H2, N2O, CO2) from solubility equilibrium behavior warrant further confirmation and theoretical investigation.     

Intercomparison of volatile organic carbon measurement techniques and data at La Porte during the TexAQS2000 Air Quality Study

The Texas Air Quality Study 2000 (TexAQS2000) investigated the photochemical production of ozone and the chemistry of related precursors and reaction products in the vicinity of Houston, TX. The colocation of four instruments for the measurement of volatile organic carbon compounds (VOCs) allowed a unique opportunity for the intercomparison of the different in-situ measuring techniques. The instruments included three gas chromatographs, each with a different type of detector, and a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) with each system designed to measure a different suite of VOCs. Correlation plots and correlation statistics are presented for species measured by more than one of these instruments. The GC instruments were all in agreement to within 10-20% (slope) with coefficients of variation (r2) of > or = 0.85. The PTR-MS agreement with other instruments was more dependent on species with some very good agreements (r2 values of approximately 0.95 for some aromatics), but isoprene, acetaldehyde and propene were substantially less highly correlated (0.55 < r2 < 0.80). At least part of these differences were undoubtedly due to the timing of sample acquisition in an environment in which VOC levels changed very rapidly on both quantitative and temporal scales.     

Fully Automated Vortex-Assisted Liquid-Liquid Microextraction Coupled to Gas Chromatography-Mass Spectrometry for the Determination of Trace Levels of Phthalate Esters in Liquor Samples

A fully automated vortex-assisted liquid-liquid microextraction (VALLME) system coupled to gas chromatography-mass spectrometry (GC/MS) was developed for the determination of phthalate esters (PAEs) in liquor samples. The whole analytical procedure, including spiking, extraction, phase separation, extractant collection, and GC/MS quantification, were automatically carried out. The use of a commercially available sample vial and a multipurpose sampler equipped with a highly efficient orbital vortex shaker facilitated the accessibility and automation of the method. Key factors, such as type and volume of the extractant, time and speed for VALLME, agitation speed and time required for phase separation, sample pH, salt effects, and matrix effects, were thoroughly investigated. Under the optimum conditions, linearity was in the range 0.05 to 120 μg L^?1. Limits of detection ranged from 0.003 to 0.006 μg L^?1. Enrichment factors were in the range 211 to 304. Reproducibility and recoveries were assessed by testing a series of liquor samples spiked with different concentrations of phthalate esters. This work provided an innovative way to automate the VALLME method and couple it on-line with GC/MS.     

Automated sampler for the measurement of non-methane organic compounds

An automated sampler has been constructed for the unattended collection of whole-air samples in Summa passivated stainless steel canisters. The sampler consists of a Viton diaphragm pump; a differential-pressure flow controller; a 2-position, 3-port valve; a 10-port multiposition valve; and a digital valve sequence programmer that controls the sequence and timing of the electrically actuated valves. All connecting tubing was constructed from Silcosteel tubing. Two configurations of the automated sampler and a passive collection system were evaluated by comparing the combined sampling precisions of the three systems with the analytic precision, derived from replicate analyses of an ambient air sample. The analytic precision was generally < +/- 5%, with higher values observed for analytes with mixing ratios in the tens of pptv. However, analytic precision values for methanol and ethanol were poor, greater than +/- 20%. Values for sampling precision were greater by about a factor of 2 than the analytic precision. The poor results for the light oxygenated hydrocarbons could be caused by sorption of the analytes in the preconcentration and sampling systems and difficulties in peak integration.     

Some insights into the gas chromatographic determination of reduced sulfur compounds (RSCs) in air

The analytical properties of four reduced sulfur compounds (RSCs), including hydrogen sulfide (H2S), methyl mercaptan (CH3SH), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), were investigated to improve the techniques for their measurements at sub-part-per-billion (sub-ppb) concentration levels. Forthis purpose, a gas chromatographic (GC) system with a pulsed-flame photometric detector (PFPD) was interfaced with a thermal desorption (TD) unit for the collection and analysis of RSCs in ambient air. The calibration results obtained by working standards of equimolar concentrations (prepared at five different concentrations of 5, 10, 20, 50, and 100 ppb) were evaluated to properly describe the detection characteristics of the GC/ PFPD setting and of different RSCs. It was observed that the absolute magnitude of calibration slopes changed among different S compounds in a consistent manner (e.g., enhanced sensitivity toward the compound of heavy molecular weight and/or high sulfur contents), while their full scales of linearity range varied in an opposite pattern. The absolute magnitude of the H2S calibration slope values was remarkably sensitive to the initial standard concentrations, while such effects were not so evident from other RSCs. The overall results of this study suggest that the GC detection of H2S by means of the bag sampling technique can suffer from the strongest variability due to the dynamic change of its calibration in accord with its initial concentration.     

Measurement of helium isotopes in soil gas as an indicator of tritium groundwater contamination

The focus of this study was to define the shape and extent of tritium groundwater contamination emanating from a legacy burial ground and to identify vadose zone sources of tritium using helium isotopes (3He and 4He) in soil gas. Helium isotopes were measured in soil-gas samples collected from 70 sampling points around the perimeter and downgradient of a burial ground that contains buried radioactive solid waste. The soil-gas samples were analyzed for helium isotopes using rare gas mass spectrometry. 3He/4He ratios, reported as normalized to the air ratio (RA), were used to locate the tritium groundwater plume emanating from the burial ground. The 3He (excess) suggested that the general location of the tritium source is within the burial ground. This study clearly demonstrated the efficacy of the 3He method for application to similar sites elsewhere within the DOE weapons complex.     

New device and method for flux-proportional sampling of mobile solutes in soil and groundwater

The importance of monitoring the transport of organic contaminants in soil and groundwater, and the pros and cons of existing sampling methods, are outlined. A new, alternative sampling method is proposed, using a passive sampler that functions as a water-permeable, semi-infinite sink for passing solutes of interest. Tracers integrated in the device store information on the volume of water passing through the sampler during the installation period. The conceptual basis of the sampling method is described. This device enables flux-proportional monitoring of the concentrations of mobile contaminants in the soil and groundwater. 14C-labeled phenanthrene (PHEN) and glyphosate (GLY) are used as case study compounds in laboratory experiments. The sorption capacities and uptake kinetics of 13 adsorbents are screened and compared, as well as the dissolution kinetics of three tracer salts: calcium citrate, calcium fluoride (CaF2), and calcium hydrogen phosphate (CaHPO4). The application of the passive sampler is then demonstrated in long-term laboratory experiments, using large soil columns under steady-state hydraulic conditions. The accumulated flux of PHEN was sampled with an accuracy of 3.6%-17.8%, using graphitized carbon, hexagonal mesoporous silica, and cross-linked polymers as adsorbents. The accumulated flux of GLY was sampled with an accuracy of 12.4%, using gamma-alumina as an adsorbent. The advantages and limitations of this new environmental monitoring method are discussed.     

Characterisation of Asturian cider apples on the basis of their aromatic profile by high-speed gas chromatography and solid-phase microextraction

Headspace solid-phase microextraction (SPME) coupled to high-speed gas chromatography with FID detector (HSGC-FID) and with quadrupole mass spectrometric detector (GC–MS) was employed to study the volatile compounds in Asturian cider apples. The optimised conditions used for characterisation of cider apple were: sample equilibration at 25 °C for 12 h, followed by PDMS–DVB fibre exposure to the headspace above the sample for 5 min and finally thermal desorption of the adsorbed substances in the injector port for GC analysis. The use of high-speed gas chromatography allowed the separation of 27 compounds in less than 8 min, reducing the analysis time in 80% compared to conventional gas chromatography. A simple, rapid and reliable method to analyze volatile compounds in cider apples has been developed. The aromatic profile of 59 apple samples included in eight apple varieties was analysed. The different apples were obtained from two consecutive harvests (2005 and 2006). The apples volatile compounds together with chemometric techniques such as principal components analysis (PCA), Bayesian analysis and linear discriminant analysis (LDA), allowed us to differentiate apples on the basis of the sweet or sharp category to which the cider apple variety belongs. Volatile compounds such as ethyl heptanoate, E-farnesene, ethyl butyrate and hexyl caprylate are closely related to cider apple cultivars of the sweet category, while propyl butyrate and butyl acetate are related to the sharp class.     

Estimation of membrane diffusion coefficients and equilibration times for low-density polyethylene passive diffusion samplers

Passive diffusion (PD) samplers offer several potential technical and cost-related advantages, particularly for measuring dissolved gases and volatile organic compounds (VOCs) in groundwater at contaminated sites. Sampler equilibration is a diffusion-type process; therefore, equilibration time is dependent on sampler dimensions, membrane thickness, and the temperature-dependent membrane diffusion coefficient (Dm) for the analyte of interest. Diffusion coefficients for low-density polyethylene membranes were measured for He, Ne, H2, O2, and N2 in laboratory experiments and ranged from 1.1 to 1.9 x 10(-7) cm2 sec(-1) (21 degrees C). Additionally, Dm values for several commonly occurring VOCs were estimated from empirical experimental data previously presented by others (Vroblesky, D. A.; Campbell, T. R. Adv. Environ. Res. 2001, 5(1), 1.), and estimated values ranged from 1.7 to 4.4 x 10(-7) cm2 sec(-1) (21 degrees C). On the basis of these Dm ranges, PD sampler equilibration time is predicted for various sampler dimensions, including dimensions consistent with simple constructed samplers used in this study and commercially available samplers. Additionally, a numerical model is presented that can be used to evaluate PD sampler concentration "lag time" for conditions in which in situ concentrations are temporally variable. The model adequately predicted lag time for laboratory experiments and is used to show that data obtained from appropriately designed PD samplers represent near-instantaneous measurement of in situ concentrations for most field conditions.     

Passive monitoring method for 3-ethenylpyridine: a marker for environmental tobacco smoke

A new method was developed to assess environmental tobacco smoke in air. The method is based on passive sampling and subsequent measurement of the concentration of 3-ethenylpyridine, a vapor-phase compound specific to tobacco smoke. Air samples were collected using a 3M organic vapor monitor. Tests were carried out in a dynamic chamber to determine the sampling rate (25.7 cm3/min). 3-Ethenylpyridine was desorbed from the sampler with 1 mL of pyridine/toluene mixture. 3-Ethenylpyridine was quantified by gas chromatography/mass spectrometry. The limit of detection was 0.01 microgram/sample, corresponding to a concentration of 0.27 microgram/m3 air calculated for a sampling period of 24 h. Field measurements were carried out to test the performance of the method. Mean concentrations ranging from 1.3 to 5.3 micrograms/m3 were measured for 3-ethenylpyridine in smoking environments, but no 3-ethenylpyridine was detected in nonsmoking environments. Active sampling using charcoal tubes was used as a reference method in the chamber tests and field measurements. Individual exposures can be easily and accurately measured by means of the passive sampler. Because of simple sample treatment, the method is also well-suited for large-scale monitoring of environmental tobacco smoke.     

Saturated zone denitrification: potential for natural attenuation of nitrate contamination in shallow groundwater under dairy operations

We present results from field studies at two central California dairies that demonstrate the prevalence of saturated-zone denitrification in shallow groundwater with 3H/ 3He apparent ages of < 35 years. Concentrated animal feeding operations are suspected to be major contributors of nitrate to groundwater, but saturated zone denitrification could mitigate their impact to groundwater quality. Denitrification is identified and quantified using N and O stable isotope compositions of nitrate coupled with measurements of excess N2 and residual NO3(-) concentrations. Nitrate in dairy groundwater from this study has delta15N values (4.3-61 per thousand), and delta18O values (-4.5-24.5 per thousand) that plot with delta18O/delta15N slopes of 0.47-0.66, consistent with denitrification. Noble gas mass spectrometry is used to quantify recharge temperature and excess air content. Dissolved N2 is found at concentrations well above those expected for equilibrium with air or incorporation of excess air, consistent with reduction of nitrate to N2. Fractionation factors for nitrogen and oxygen isotopes in nitrate appear to be highly variable at a dairy site where denitrification is found in a laterally extensive anoxic zone 5 m below the water table, and at a second dairy site where denitrification occurs near the water table and is strongly influenced by localized lagoon seepage.     

Microfabricated gas chromatograph for on-site determination of trichloroethylene in indoor air arising from vapor intrusion. 1. Field evaluation

Results are presented of inaugural field tests of two identical prototype microfabricated gas chromatographs (μGC) adapted for the in situ determination of trichloroethylene (TCE) in indoor air in support of vapor intrusion (VI) investigations. Each μGC prototype has a pretrap and partially selective high-volume sampler of conventional design, a micromachined-Si focuser for injection, dual micromachined-Si columns for separation, and an integrated array of four microscale chemiresistors with functionalized gold nanoparticle interface films for multichannel detection. Scrubbed ambient air is used as the carrier gas. Field-generated calibration curves were linear for injected TCE masses of 26-414 ng (4.8-77 ppb·L; r(2) > 0.98) and the projected single-sensor detection limit was 0.052 ppb for an 8-L air sample collected and analyzed in 20 min. Consistent performance between the prototypes and good medium-term stability were shown. Above the mitigation action level (MAL) of 2.3 ppb for the field-test site, μGC TCE determinations fell within ±25% of those from the reference method for 21 of 26 measurements, in the presence of up to 37 documented background VOCs. Below the MAL, positive biases were consistently observed, which are attributable to background VOCs that were unresolvable chromatographically or by analysis of the sensor-array response patterns. Results demonstrate that this type of μGC instrument could serve the need for routine TCE determinations in VI-related assessment and mitigation efforts.     

A water extraction, static headspace sampling, gas chromatographic method to determine MTBE in heating oil and diesel fuel

A method was developed to determine the fuel/water partition coefficient (KMTBE) of methyl tert-butyl ether (MTBE) and then used to determine low parts per million concentrations of MTBE in samples of heating oil and diesel fuel. A special capillary column designed for the separation of MTBE and to prevent coelution and a gas chromatograph equipped with a photoionization detector (PID) were used. MTBE was partitioned from fuel samples into water during an equilibration step. The water samples were then analyzed for MTBE using static headspace sampling followed by GC/PID. A mathematical relationship was derived that allowed a KMTBE value to be calculated by utilizing the fuel/water volume ratios and the corresponding PID signal. KMTBE values were found to range linearly from 3.8 to 10.9 over a temperature range of 5-40 degrees C. This analysis method gave a MDL of 0.7 ppm MTBE in the fuel and a relative average accuracy of +/-15% by comparison with an independent laboratory using purge and trap GC/ MS analysis. MTBE was found in home heating oil in residential tanks and in diesel fuel at service stations throughout the state of Connecticut. The levels of MTBE were found to vary significantly with time. Heating oil and diesel fuel from terminals were also found to contain MTBE. This research suggests thatthe reported widespread contamination of groundwater with MTBE may also be due to heating oil and diesel fuel releases to the environment. used extensively for the past 20 years as a gasoline additive (up to 15 wt %) to reduce automobile carbon monoxide and hydrocarbon emissions. The fact that MTBE is highly soluble in water (approximately 5 wt %) (3) and chemically inert when compared to other fuel constituents causes it to be often detected at high concentrations in groundwater in the vicinity of gasoline spills. The EPA has reported that low levels of MTBE in drinking water (above 40 microg/L) may cause unpleasant taste and odors and has designated MTBE as a possible human carcinogen (4). Past studies have concentrated on the reporting of MTBE levels in groundwater near gasoline spills. Happel et al. reported an MTBE occurrence rate of approximately 78% at locations where hydrocarbons have impacted groundwater (5). Johnson et al. estimate that 9,000 leaking underground fuel tanks have caused MTBE contamination at community water supplies in the 31 states surveyed (excluding California and Texas) (6). Robbins et al. reported finding a significant number of MTBE detections in groundwater samples taken at sites in Connecticut known to be contaminated by heating oil spills (7). Later, this same research group reported finding MTBE contamination to range from 9.7 to 906 mg/L in heating oil and from 74 to 120 mg/L in diesel fuel in samples collected from storage tanks in Connecticut (8). The method used to analyze these samples was based on fuel-water partitioning and GC analysis. This present study provides the detailed basis for that analytical method. MTBE fuel-water partition coefficients as a function of temperature, which are critical to the method, are also presented. This study also reports on variations in MTBE levels as a function of time observed at several residences and a service station. Analytical results are reported for samples taken from terminals as part of an effort to assess the sources of MTBE in heating oil and diesel fuel.     

Characterization and comparison of three passive air samplers for persistent organic pollutants

The accumulation of persistent organic pollutants by three passive sampling media--semipermeable membrane devices (SPMDs), polyurethane foam (PUF) disks, and an organic-rich soil--was investigated. The media were exposed to contaminated indoor air over a period of 450 days, and concentrations in the air and in the media were monitored for individual polychlorinated biphenyl (PCB) congeners and polychlorinated naphthalene homologue groups. Uptake was initially linear and governed by the surface area of the sampler and the boundary layer airside mass transfer coefficient (MTC). Mean values of the MTC were 0.13, 0.11, and 0.26 cm s-1 for SPMD, PUF, and soil, respectively. As the study progressed, equilibrium was established between ambient air and the passive sampling media for the lower molecular weight PCB congeners. This information was used to calculate passive sampler-air partition coefficients, KPSM-A. These were correlated to the octanol-air partition coefficient, and the resulting regressions were used to predict KPSM-A for the full suite of PCBs. Information on MTC, KPSM-A, surface area, and effective thickness of each sampler was used to estimate times to equilibrium for each medium. These ranged from tens of days for the lower molecular weight congeners to tens of years for the higher molecular weight PCBs. Expressions were also developed to relate the amount of chemical accumulated by the passive sampling media to average ambient air concentrations over the integration period of the sample.     

Characterizing uptake kinetics of PAHs from the air using polyethylene-based passive air samplers of multiple surface area-to-volume ratios

Polyethylene passive sampling devices (PSDs) were deployed to investigate how passive samplers of multiple surface area-to-volume ratios could be used to characterize uptake kinetics for polyaromatic hydrocarbons (PAHs). Theoretically, uptake profiles for different thickness PSDs of the same surface area should show the following: where uptake is linear, the amount of compound accumulated in the different PSDs will be the same and where equilibrium is approached, the amount accumulated by the different PSDs will be proportional to sampler thickness. Polyethylene sheets of the same surface area and approximately 100 and 200 microm thickness were collected after 30, 60, and 90 days of exposure along with samples from a codeployed high volume sampler. Twelve priority pollutant PAHs could be routinely quantified in replicate PSDs. Overall, reproducibility between replicate PSDs was satisfactory, with normalized differences rarely exceeding 25%. The smallest analytes quantified, fluorene, phenanthrene, and anthracene, were shown to approach equilibrium during the deployment period, whereas uptake for fluoranthene and pyrene moved into the curvilinear stage. For most of the larger molecular weight PAHs such as indeno[1,2,3-cd]pyrene, uptake could be described using a linear uptake model. Preliminary sampling rates for the compounds which remained in the linear stage of uptake ranged between 0.5 and 1.5 m3 d(-1) dm(-2). Sampler to air partition coefficients were estimated for PAHs which approached equilibrium and predicted for some of the other compounds. Results suggest that a single deployment of PSDs with multiple surface area-to-volume ratios can be sufficient to determine whether uptake was linear or approaching equilibrium for a range of PAHs.     

Analysing organochlorine pesticides in strawberry jams using GC-ECD, GC-MS/MS and QuEChERS sample preparation

This paper describes a comparison of adaptations of the QuEChERS (quick, easy, cheap, effective, rugged and safe) approach for the determination of 14 organochlorine pesticide (OCP) residues in strawberry jam by concurrent use of gas chromatography (GC) coupled to electron capture detector (ECD) and GC tandem mass spectrometry (GC-MS/MS). Three versions were tested based on the original QuEChERS method. The results were good (overall average of 89% recoveries with 15% RSD) using the ultrasonic bath at five spiked levels. Performance characteristics, such as accuracy, precision, linear range, limits of detection (LOD) and quantification (LOQ), were determined for each pesticide. LOD ranged from 0.8 to 8.9 μg kg(-1); LOQ was in the range of 2.5-29.8 μg kg(-1); and calibration curves were linear (r(2)>0.9970) in the whole range of the explored concentrations (5-100 μg kg(-1)). The LODs of these pesticides were much lower than the maximum residue levels (MRLs) allowed in Europe for strawberries. The method was successfully applied to the quantification of OCP in commercially available jams. The OCPs were detected lower than the LOD.     

介质阻挡放电氦等离子体-气相色谱测定绿豆中脂肪酸含量

基于介质阻挡放电氦等离子体-气相色谱结合微型样品前处理方式,建立绿豆中脂肪酸含量的快速测定方法,采用石英毛细管柱HP-88（100 m×0.25 mm,0.25 μm）（88%-氰丙基/芳基-聚硅氧烷固定液）,载气为超纯氦气（纯度99.999 9%）,载气流量为1.5 mL/min,柱温为程序升温,进样口温度250 ℃,隔垫吹扫流量为3mL/min,分流比为1∶60,检测器温度为280 ℃,等离子体放电气体流量为40 mL/min,进样体积为1 μL;样品中目标物采用异辛烷萃取,氢氧化钾-甲醇甲酯化后上机分析。实验结果表明,绿豆样品中8 种脂肪酸甲酯检测灵敏度在0.105～0.196 μg/mL之间,相对标准偏差在1.04%～1.35%之间。所建方法所需样品量及化学试剂少,样品前处理简单快速,重现性好,能够精确测定绿豆中脂肪酸含量。