Portable Gas Chromatograph Research Articles

Fast on‐site determination of tetrahydrothiophene in natural gas with a portable micro gas chromatograph: A feasibility study

Fast on‐site determination of tetrahydrothiophene in natural gas with a portable micro gas chromatograph: A feasibility study

Terpenes in a conifer forest: Detection at sub-parts per billion level without sample preconcentration

Abstract In a natural atmosphere free from anthropogenic emissions, terpenes constitute a major part of the biogenic hydrocarbon family. The study of their involvement in chemical reactions with various oxidants in the atmosphere requires continuous and accurate checking of their diurnal concentration variations. In past studies, the ever present sample preconcentration step with large sample volumes is expected to be associated with the problems of sample loss or chemical modifications in addition to their limitations on the measurement frequency. To improve upon these drawbacks, a commercially available microprocessor-based portable gas chromatograph with an ultra-sensitive detector was successfully tested and used for in situ measurements. With a direct sample volume of a few hundred microlitres of ambient air and suitable selection of the column packing material, quick separation of the various components was achieved. Excellent operational features and on-line calibration with pure samples allowed accurate and instant measurements during field studies. The photoionization (PI) detector allowed high S/N ratio even at sub-parts per billion level concentration of the hydrocarbons. Data collected over a one-year period under varying meteorological conditions from a conifer forest situated at Gulmarg (34°03′N, 74°24′E, 2650 m MSL) indicates the suitability of this system for remote field studies and also throws light on the lifecycle of these hydrocarbons in the natural atmosphere. The different hydrocarbons measured in this evaluation study includes isoprene, α-pinene and β-pinene.

HVEM of crystallization of amorphous TiNi shape memory films

TiNi alloys, well-known for their shape memory properties that arise due to a martensitic transformation, have recently been considered for application as thin film actuators. Although various methods of thin film preparation have been considered, deposition via d.c. magnetron ion sputtering provides for reproducible film formation as well as possible integration of a TiNi film as a micromachine with a semiconductor device. When sputter deposited at room temperature, the as-deposited films have an amorphous structure. These films can be bent into a particular macroscopic shape prior to crystallization, thereby setting the parent (memory) shape. When used as thin film actuators, TiNi shape memory alloys are quite cost efficient, as compared to the prohibitive manufacturing costs typical when producing bulk shape memory devices. In addition, thin film shape memory devices may be cooled much more quickly than a bulk part, and reversible transformation cycles are achieved in only milliseconds. Applications being considered for these shape memory thin films are as microactuators in optical storage devices and as microvalves in portable gas chromatographs.

Field Determination of Geological/Chemical Properties of an Aquifer by Cone Penetrometry and Headspace Analysis

AbstractThe cone penetrometer with pore pressure measurements was first introduced in 1975. It is generally regarded in the geotechnical community as one of the most efficient tools for stratigraphic logging of soft soils. Recently, the conventional cone penetrometer has been coupled with a porous probe ground‐water sampler for environmental applications.This coupled system was used to perform soil logging, collect ground‐water samples, and evaluate hydraulic conductivity in an effort to determine the extent and preferential flow pathway(s) of a soluble hydrocarbon plume in a Texas aquifer. Ground‐water samples collected by a porous probe sampler were analyzed for hydrocarbon content by a portable gas chromatograph with a photoionization detector (GC/PID) to characterize the extent of the soluble organic plume and provide a field evaluation of ground‐water quality. Aqueous concentrations of hydrocarbons calculated from vapor headspace measurements by this technique were in good agreement with direct concentration measurements obtained in the laboratory using standard EPA ground‐water analytical procedures. This field procedure makes it possible to efficiently use cone penetrometry equipment in less characterized areas allowing rapid delineation of volatile organic plumes by the headspace analysis.Interpretation of the cone penetrometer test data located a buried channel on the site aligned in an east‐west depositional direction. To the north and south of the channel, the soils exhibited reduced hydraulic conductivity due to their respective soil type or depositional density. Analyses of ground‐water samples collected from the area confirmed that soluble hydrocarbon migration was following the more permeable channel. In addition, depth selective ground‐water sampling recorded sharp changes in the vertical concentration profiles indicating that macroscopic vertical dispersion may be negligible at this site.

Comparison of portable gas chromatographs and passivated canisters for field sampling airborne toxic organic vapors in the United States and the USSR

Collection of samples in passivated canisters is widely used in analysis of trace volatile organic compounds in air because preconcentration is usually required to detect analytes. Sample integrity can be comprised by deterioration or artifact formation during storage and preconcentration. A laboratory-tested portable gas chromatograph (PGC) equipped with a highly sensitive photoionization detector (PID) equipped with a highly sensitive photoionization detector (PID) offers the advantage of near real-time data without preconcentration, but its limitations as a field-portable instrument must be recognized. This paper presents data produced simultaneously by the canister/TO-14 method and by PGCs. Data were obtained in US and overseas field studies at industrial, hazardous waste, and roadway sites. Field results suggest that a combination of canister and PGC methods offers a synergistic approach to source assessment measurements.

A field method for measuring solvent vapors in exhaled air--application to styrene exposure.

A method is described for measuring solvent vapors in mixed-exhaled air. The subject exhales through a carbon-containing tube connected to a Wright respirometer. Adsorbed vapors are subsequently eluted by carbon disulfide and analyzed by gas chromatography. Twenty-minute exposures to styrene and the corresponding concentrations of styrene in the breath and venous blood were repeatedly measured for two subjects. Regression analyses indicated that the breath measurements were highly correlated with both the exposures and the blood concentrations of styrene. In another study, styrene was measured simultaneously in the mixed-exhaled air by this technique and in the end-exhaled air by a portable gas chromatograph. The mixed-exhaled air obtained with this method contained about half alveolar air. Analysis of the components of the variance obtained from all the data indicated that the error in measurement by this method was about one-fourth of the total variance.

Rapid analysis of tracer gases for measurement of infiltration rates of indoor air using GC.

Tracer gases such as SF6 and CH4 have often been used to measure infiltration rates of indoor air. These gases have generally been measured by infrared spectroscopic analysis. Use of this method, however, sometimes causes problems because a lot of sample gases are required. On the other hand, a portable gas chromatograph has been developed in our previous work, that is equipped with a short-length capillary column and a micro thermal conductivity detector. This paper then refers to an application of the gas chromatograph to measure several sorts of tracer gases. Study was focused both on the optimum condition of tracer gas analysis and on their calibration method using air as a reference gas. It was consequently found that the introduction of PoraPLOT Q of 8 m length to the capillary column could shorten analysis time up to 1 min to analyze the tracer gases such as CH4, N2O, SF6 and C2H4. Thermal response values of the tracer gases against air (nitrogen+oxygen) under the optimum condition were obtained. The determined values of the tracer gases; using these values, agreed with those using a reference gas mixture. This result suggests that the calibration method by the use of thermal response values of the tracer gases is able to apply to the quantitative analysis of several sorts of tracer gases. It also appeared that the lower limits of detection of N2O and SF6 were enhanced to 2 ppm.

CAPILLARY GAS CHROMATOGRAPHY USING CARBON DIOXIDE AS THE CARRIER GAS

Capillary Gas Chromatography(GC) system using carbon dioxide as the carrier gas was evaluated. The outdoor measurement is often required in environmental analysis using portable GC. But portability and operation time is limited by the carrier gas cylinder volume. We tried to solve this problem by using liquefied gas, such as CO 2 , instead of he as the carrier gas. We compared the differences between CO 2 and he and analyzed environmental air samples using different types of capillary columns. Similar resolution was obtained at flow rate around 1 ml/min in both cases

Analytical Performance of Four Portable Gas Chromatographs Under Field Conditions

A field evaluation of the performance of four portable gas chromatographs was conducted at two field sites, one in the Pacific Northwest (chlorinated solvent contamination) and one in the Desert Southwest (primarily jet fuel contamination). The purpose of the study was to compare the performance of four portable GCs under the same conditions. The gas chromatographs had either electron-capture detectors or photoionization detectors. The study evaluated instrument linearity, instrument detection limits, retention time stabilities, response factor stability, and chromatographic performance. Standards and samples contained 1, 1, 2, 2-tetrachloroethane, trichloroethene, tetrachloroethane, 1, 1, 1-trichloroethane, benzene, toluene, and ethylbenzene. In order to ensure data comparability, the same model wide-bore column and computing integrator were used with each instrument, where possible. Significant differences in the performance of the four models were detected under the specific conditions used for this study. The results indicate the need to fully characterize the performance of portable instruments before field use so that appropriate quality control measures can be planned and implemented based on the performance of a specific analytical system.

A Surface‐Flux Measurement Method for Screening Contamination from Volatile Organic Compounds

AbstractMeasurement of the vapor flux from volatile organic compounds (VOCs) provides a rapid means for screening large areas of potential contamination. The vapor flux is determined from the rate of VOC concentration buildup inside a 3.1L accumulator device that is sealed to the surface of the contaminated soil. After the VOC concentrations are allowed to increase for a few minutes, they are analyzed with a portable gas chromatograph or a total organic vapor analyzer.The measurement approach was evaluated at a field site in an area where the ground water and soil had been impacted with Jet Fuel No. 4 (JP‐4). An indication of the areal extent of impact was determined by mapping the surface VOC vapor flux. The pattern revealed by the flux measurements was found to coincide, in rough outline, with the known extent of toluene concentrations in the ground water and with conventional soil‐gas survey results. In addition, a mathematical model describing VOC diffusion into the accumulator device was verified by performing laboratory measurements of the surface VOC vapor flux on a sandbox designed to simulate a hazardous waste site.

Performance evaluation materials for the analysis of volatile organic contaminants in soil: A preliminary assessment

Abstract During an evaluation of field portable gas chromatographs (GC), site‐specific performance evaluation materials (PEM) were prepared and used as quality control samples. Clean soils from two contaminated sites were spiked with various volatile organic compounds. The PEM were shipped to the field via air carrier and analyzed by GC. The PEM samples were also shipped back to the laboratory and analyzed as double blind samples on a GC and a gas chromatograph / mass spectrometer (GC/MS). PEM samples which were held in the laboratory without being shipped were also analyzed. For GC analyses a static headspace method revealed highly variable recoveries for both shipped and unshipped PEM. An operationally‐defined headspace calibration was used to quantitate the amount of analyte remaining in the soil at various holding times and under various shipment scenarios. The influence of soil characteristics and volatile compound properties, and the effects of holding time and shipping on analyte stability in actua...

Decreased Sensitivity of Photoionization Detector Total Organic Vapor Detectors in the Presence of Methane

The reduction in sensitivity of the Photoyae TIP, TIP-1, and the H-NU101 total organic vapor analyzers equipped with photoi-onization detectors (PID) to toluene and gasoline in the presence of methane (0.5–5.0% v/v) was examined. The results showed an exponential decrease in detector sensitivity, with a reduction of about 30% for 03% methane and 90% for 5% methane. A Photovac TIP (PID), a Century OVA equipped with a flame ionization detector (FID), and a Photovac 10S50 portable gas chromatograph (PID) were used in a soil gas survey to map the areal extent of gasoline contamination. The survey area was paved, and comparison of FID and PID response showed that methane was widespread under the asphalt, including areas where gas chromatography showed no gasoline contamination. Two soil gas samples analyzed in the laboratory showed concentrations of 0.23% and 0.99% methane by volume. Because high concentrations of biogenic methane are found in the environment, this loss of sensitivity may be important when PID...

Morning Transition Tracer Experiments in a Deep Narrow Valley

Abstract Three sulfur hexafluoride atmospheric tracer experiments were conducted during the post-sunrise temperature inversion breakup period in the deep, narrow Brush Creek Valley of Colorado. Experiments were conducted under clear, undisturbed weather conditions. A continuous elevated tracer plume was produced along the axis of the valley before sunrise and the behavior of the plume during the inversion breakup period was detected down-valley from the release point using an array of radio-controlled sequential bag samplers, a vertical SF6 profiling system carried on a tethered balloon, two portable gas chromatographs operated on a sidewall of the valley, and a continuous real-time SF6 monitor operated from a research aircraft. Supporting meteorological data came primarily from tethered balloon profilers. The nocturnal elevated plume was carried and diffused in down-valley flows. After sunrise, convective boundary layers grew upward from the sunlit valley surfaces, fumigating the elevated plume onto the ...

Screening of Ground Water Samples for Volatile Organic Compounds Using a Portable Gas Chromatograph

AbstractA portable gas chromatograph was used to screen 32 ground water samples for volatile organic compounds. Seven screened samples were positive; four of the seven samples had volatile organic substances identified by second‐column confirmation. Four of the seven positive, screened samples also tested positive in laboratory analyses of duplicate samples. No volatile organic compounds were detected in laboratory analyses of samples that headspace screening indicated to be negative. Samples that contained volatile organic compounds, as identified by laboratory analysis, and that contained a volatile organic compound present in a standard of selected compounds were correctly identified by using the portable gas chromatograph. Comparisons of screened‐sample data with laboratory data indicate the ability to detect selected volatile organic compounds at concentrations of about 1 microgram per liter in the headspace of water samples by use of a portable gas chromatograph.

Evaluation of a Carbon Adsorption Method for Sampling Gasoline Vapors in the Subsurface

AbstractMonitoring of the vapor phase has emerged as a very convenient method for detecting volatile organic contaminants in the subsurface. It can provide a reliable way of placing ground water monitoring and recovery wells. The most common method uses a driveable ground probe (DGP) to extract a vapor‐phase sample followed by direct injection of the vapor into a portable gas chromatograph (GC). However, many regional offices of regulatory agencies and consultants do not have ready access to such equipment. This research explores an alternative–the carbon adsorption method—in which the vapor is withdrawn by the DGP but concentrated on a small activated carbon trap (150mg). The carbon traps can be returned to a central laboratory for solvent extraction and GC analysis. This provides the advantages of increased sensitivity, reduction in field equipment and convenience of in‐lab analyses (multiple GC injections are possible). A simple DGP and carbon trap system was constructed and tested at a field site. Vapor‐phase concentrations of target compounds present in gasoline were mapped quite conveniently, ranging from 10,000μg/liter (vapor phase) to less than 10μg/L. These concentrations were also shown to decrease in the direction of the ground surface, as expected. Measurements of target compounds in soil showed that the vapor phase contributed a large fraction of the total contaminant burden where a non‐aqueous‐phase layer (NAPL) had been identified; as important, however, is the rather uniform contamination of the soil outside the NAPL region. Finally, the concentrations of target compounds in the vapor phase and ground water could be related in a manner roughly described by a simple equilibrium model, although exceptions were noted.

Ambient Capillary Chromatography of Volatile Organics With a Portable Gas Chromatograph

La stabilite du detecteur a photoionisation et la resolution des composes organiques sont ameliorees dans l'appareil portatif par l'utilisation d'une colonne capillaire

Subsurface Venting of Vapors Emanating from Hydrocarbon Product on Ground Water

AbstractThe results of an API‐sponsored pilot‐scale subsurface venting system study are presented. The purpose of this study was to evaluate the effectiveness of forced venting techniques in controlling and removing hydrocarbon vapors from a subsurface formation. Both qualitative and quantitative sampling and analytical procedures were developed to measure hydrocarbon vapors extracted from the soil. Vapor recovery and equivalent liquid product recovery rates were measured at each test cell evacuation rate.Two identical test cells were installed. Each cell contained 16 vapor monitoring probes spaced at distances from 4 to 44 feet from a vapor extraction (vacuum) well. Each cell was also configured with two air inlet wells to allow atmospheric air to enter the subsurface formation. The vapor monitoring probes were installed at three discrete elevations above the capillary zone. In situ vapor samples were obtained periodically from these probes to measure changes in vapor concentration and composition while extracting vapors from the vacuum well at three different flow rates (18.5 scfm, 22.5 scfm and 39.8 scfm). In situ vapor samples were analyzed using a portable gas chromatograph to quantify and speciate the vapors. Vacuum levels were also measured at each vapor sampling probe and at the vacuum well.The soil venting techniques evaluated during this study offer an alternative approach for controlling and eliminating spilled or leaked hydrocarbons from sand or gravel formations of high porosity and moderate permeability. These techniques may also be used to augment conventional liquid recovery methods. The data collected during this study will be useful in optimizing subsurface venting systems for removing and controlling hydrocarbon vapors in soil. Study results indicate pulsed venting techniques may offer a cost‐effective means of controlling or eliminating hydrocarbon vapors in soil.

Modification and field testing of a portable gas chromatograph forin situ acetylene reduction activity assay of tropical soils

Small modifications of the Mallard/Holfeld/LaRue GC allow indirect measurement of biological N2-fixation in tropical soils even in remote locations. Examples of ARA from Philippine rice fields are given.

Effective Controls for Ethylene Oxide—A Case Study

Abstract The National Institute for Occupational Safety and Health (NIOSH) has studied the control of ethylene oxide (EtO) exposures associated with hospital sterilizers to determine which combinations of control measures are most effective. This case study describes the evaluation of controls at one hospital. The hospital had a gas sterilizer which used a mixture of EtO (12 percent by weight) in Freon-12[rgrave]. The sterilizer was retrofitted with the manufacturer's control system consisting of a ventilated air gap, local exhaust ventilation above the sterilizer door, and cycle modifications for additional end-of-cycle air flushes. Personal and area samples for EtO were collected with charcoal tubes for laboratory analysis (NIOSH method #1607) and in gas sampling bags for on-site analysis with a portable gas chromatograph. The area in front of the sterilizer was also monitored with an infrared analyzer. All full-shift personal exposures and area concentrations were less than 0.05 ppm. Infrared monitoring showed no potential exposure in front of the sterilizer due to the purge cycle or opening the door a few inches for 15 minutes prior to transferring the load to an aerator. The EtO emitted during the post-sterilization chamber evacuation cycles was controlled by isolating all but the front of the sterilizer in an adequately ventilated recess room. The ventilation rate compared favorably with three design criteria. The airflow created by the slot hood above the sterilizer door controlled emissions from the sterilizer when the door was opened a few inches, consistent with a design equation for a flanged slot. General ventilation was not an important factor in this control strategy. Additional control measures were needed to deal with possible occasional and/or incidental exposures to potentially high concentrations of EtO. Mortimer, V. D.; Kercher S. L; O'Brien, D. M. Effective controls for ethylene oxide—a case study.

An improved portable gas chromatograph for the measurement of nitrogen-fixing activity

An improved portable gas chromatograph using a gas sensor as a detector was constructed and its efficiency was tested for the measurement of nitrogen-fixing activity. The ethylene was quantitatively determined by this gas chromatograph at the same sensitivity as that of a conventional gas chromatograph using a flame ionization detector, when the amount of ethylene injected was less than 1.5 nmol. The equipment was found to be handy and inexpensive, and suitable for the measurement of acetylene reduction activity in the field.