Automated Gas Chromatography Research Articles

A Gas Chromatographic Separation for the H and C Stable Isotope Ratio Determination of Coal Compounds

A new, completely automated gas chromatography technique has been developed to separate the different gaseous compounds produced during underground coal gasification for their (13)C/(12)C and D/H isotope ratio measurements. The technique was designed for separation and collection of H(2), CO, CO(2), H(2)O, H(2)S, CH(4), and heavier hydrocarbons. These gaseous compounds are perfectly separated by the gas-phase chromatograph and quantitatively sent to seven combustion and collection lines. H(2), CO, CH(4), and heavier hydrocarbons are quantitatively oxidized to CO(2) and/or H(2)O. The isotopic analyses are performed by the sealed-tube method. The zinc method is used for reduction of both water and H(2)S to hydrogen for D/H analysis. Including all preparation steps, the reproducibility of isotope abundance values, for a quantity higher than or equal to 0.1 mL of individual components in a mixture (5 mL of gases being initially injected in the gas chromatograph), is ±0.1‰ for δ(13)C(PDB) and ±6‰ for δD(SMOW).

Determination of aromatic hydrocarbons in urban air of Rome

Aromatic hydrocarbons were measured in Rome during 1992–1993 by means a differential optical absorption spectrometer (DOAS) and an automatic gas chromatograph (VOC analyzer). The mean distribution of aromatic hydrocarbons was: benzene 12.6%, toluene 35.4%, and remaining species 42%. The mean yearly concentrations of toluene (128 and 138 μg m −3) were 2–3 times higher than those of benzene (40 and 47 μg m −3). The highest concentrations of aromatic hydrocarbons were measured during the stagnant winter period. The diurnal behavior of aromatic hydrocarbons suggests that motor exhaust emissions are their dominant source. The different reactivities of benzene and toluene during photochemical smog episodes were discussed.

Technique for monitoring ozone precursor hydrocarbons in air at photochemical assessment monitoring stations: Sorbent preconcentration, closed-cycle cooler cryofocusing, and GC-FID analysis

An automated gas chromatograph (autoGC) system that may be used to collect and analyze both polar and nonpolar volatile organic compounds in ambient air has been evaluated. This system combines the use of dual multiadsorbent traps for sampling 57 min h −1 at ambient temperature, a dry helium purge to remove residual water from the sorbents, thermal desorption of analytes onto a Stirling-cooled trap for refocusing, and GC-flame ionization detection (FID). Method detection limits (MDLs), linearity, cleanliness, precision, and accuracy of the autoGC were determined for a set of 57 ozone precursor hydrocarbons. For most of the compounds tested, MDLs were less than 0.40 ppbv, the FID response was linear over the 5–40-ppbv range, and the trap-to-trap precision was ± 10%. This autoGC was found to be a reliable system that would be suitable for use in field sites such as the Photochemical Assessment Monitoring Stations network, which is being implemented in the United States of America.

Gas chromatography mass spectrometry analysis of volatile organic trace gases at Mauna Loa Observatory, Hawaii

Volatile organic trace gases in the remote troposphere at the Mauna Loa Observatory were identified in July and August 1992 during the Mauna Loa Observatory Photochemical Experiment (MLOPEX 2) using an in situ fully automated gas chromatography mass spectrometry (GCMS) instrument. Identification was obtained for 65 organic compounds, 7 additional compounds were identified tentatively. Four target parts per trillion (ppt)‐level species were detected in the selected ion monitoring mode (SIM). The experimental data show typical background air characteristics; for example, abundance of long‐lived compounds such as halogenated hydrocarbons during all measurement periods. Volatile organic compounds (VOCs) from local sources from the island were also seen during daytime upslope flow conditions. These included short‐lived biogenic hydrocarbons such as isoprene and monoterpenes and typical emissions from combustion processes such as alkylated aromatics.

Interfacing a Robotic Station with a Gas Chromatograph for the Full Automation of The Determination of Organochlorine Pesticides in Vegetables

Abstract A fully automated method for the determination of organochlorine pesticides in vegetables is proposed. The overall system acts as an “analytical black box” because a robotic station performs the preliminary operations, from weighing to capping the leached analytes and location in an autosampler of an automated gas chromatograph with electron capture detection. The method has been applied to the determination of lindane, heptachlor, captan, chlordane and metoxychlor in tea, marjoram, cinnamon, pennyroyal, and mint with good results in most cases. A gas chromatograph has been interfaced to a robotic station for the determination of pesticides in vegetables Manuscript 1061

Atmospheric methane at Mauna Loa and Barrow observatories: Presentation and analysis of in situ measurements

In situ methane (CH4) measurement techniques and data from the NOAA Climate Monitoring and Diagnostics Laboratory observatories at Mauna Loa, Hawaii, and Barrow, Alaska, are presented. For Mauna Loa, the data span the time period April 1987 to April 1994. At Barrow the measurements cover the period January 1986 to January 1994. Sixty air samples per day were measured with a fully automated gas chromatograph using flame ionization detection. Details of the experimental methods and procedures are given. Data are presented and assessed over various timescales. The average peak to peak seasonal cycle amplitudes obtained from four harmonics fitted to the detrended data were 25.1 ppb at Mauna Loa and 47.2 ppb at Barrow. When the seasonal cycle amplitude during each calendar year was determined as the difference between the maximum and minimum value from a smooth curve fitted to the data, the average amplitudes were (30.6±4.2) ppb at Mauna Loa and (57.5±11.4) ppb at Barrow. A discrepancy exists between these two methods due to the temporal variability in the positions of the seasonal maxima. The average trend at Mauna Loa was 9.7 ppb yr−1, but this trend was observed to decrease at a rate of 1.5 ppb yr−2. For Barrow the average trend was 8.5 ppb yr−1, and the rate of decrease in the trend was 2.1 ppb yr−2. At Mauna Loa, a diurnal cycle was sometimes observed with an amplitude of up to 10 ppb when averaged over 1 month.

Hydrocarbon Measurements During the 1992 Southern Oxidants Study Atlanta Intensive: Protocol and Quality Assurance

Abstract A major component of the Southern Oxidants Study (SOS) 1992 Atlanta Intensive was the measurement of atmospheric nonmethane hydrocarbons. Ambient air samples were collected and analyzed by a network of strategically located automated gas chromatography (GC) systems (field systems). In addition, an extensive canister sampling network was deployed. Combined, more than 3000 chromatograms were recorded. The SOS science team targeted for quantitative analysis 56 compounds which may be substantial contributors to ozone formation or used as air mass tracers. A quality assurance program was instituted to ensure that good measurements were being made throughout the network for each target compound. Common, high-quality standards were used throughout the network. The performance of individual field systems was evaluated during the intensive through the analysis of challenge mixtures. This methodology helped to identify and correct analytical problems as they arose.

An automated instrument for the analysis of atmospheric dimethyl sulfide and carbon disulfide

An automated gas Chromatograph (GC) has been developed for the analysis of the atmospheric concentrations of dimethyl sulfide (DMS) and carbon disulfide (CS 2) at the Australian Baseline Air Pollution Station Cape Grim. The system comprises cryogenic concentration of DMS and CS 2 from 4 I of air after oxidant and water removal, capillary gas chromatography, and sulfur chemiluminescence detection. Calibtation is by injection of a known quantity of methylethyl sulfide (MES) as an internal standard into the sampled air stream. Detection and quantitation of DMS and CS 2 in the range of 5 to 500 ng/m 3, typical of the annual concentration variation of DMS and CS 2 at Cape Grim, has been achieved with a sampling frequency of 2 samples per hour and a detection limit of 10 pg S per compound. A comparison of results from the automated GC and those obtained by a gold-coated glass wool trapping method with atomic emission detection is presented.

Vehicle-Related Hydrocarbon Source Compositions from Ambient Data: The GRACE/SAFER Method

The composition of three volatile hydrocarbon sources (emissions from vehicles in motion, evaporation of whole gasoline, and gasoline headspace vapor) have been derived from 550 ambient, hourly concentration measurements of 37 C[sub 2]-C[sub 9] volatile organic compounds (VOC). The measurements were made by automated gas chromatograph in Atlanta, GA, during the summertime of 1990. The source compositions were obtained by a novel combination of graphical analysis and multivariate receptor modeling methodologies: GRACE (Graphical Ratio Analysis for Composition Estimates) and SAFER (Source Apportionment by Factors with Explicit Restrictions). For the relatively unreactive hydrocarbon species, the ambient-derived source compositions were in good agreement with direct source measurements made in Atlanta concurrent with the ambient measurements. The prominence of the whole gasoline profile in the ambient data was an unexpected result. The GRACE/SAFER method may provide a cost-effective alternative to the usual direct source measurement of profiles. 22 refs., 3 figs., 5 tabs.

Comparison of Nonmethane Organic Compound Concentration Data Collected by Two Methods in Atlanta

Title I of the Clean Air Act Amendments of 1990 calls for “enhanced monitoring” of ozone, which is planned to include measurements of atmospheric non-methane organic compounds (NMOCs). NMOC concentration data gathered by two methods in Atlanta, Georgia during July and August 1990 are compared in order to assess the reliability of such measurements in an operational setting. During that period, automated gas chromatography (GO) systems (Field systems) were used to collect NMOC continuously as one-hour averages. In addition, canister samples of ambient air were collected on an intermittent schedule for quality control purposes and analyzed by laboratory GC (the Lab system). Data from the six-site network included concentrations of nitrogen oxides (NOX), carbon monoxide (CO), ozone, total NMOC (TNMOC), and 47 identified NMOCs. Regression analysis indicates that the average TNMOC concentration from the Lab system is about 50 percent higher than that from the Field system, and that the bulk of the difference i...

Measurements of peroxyacetyl nitrate at a remote site in the southwestern United States: tropospheric implications

Peroxyacetyl nitrate (PAN) measurements were taken at a remote site in the southwestern United States from October 1987 through January 1989 by using an automated gas chromatograph with electron capture detection. The monthly mean PAN concentrations were found to correlate well with temperature, as PAN levels were higher in the colder periods, consistent with PAN's thermochemical stability. PAN values ranged from below detection limits of 0.030-1.91 ppbv (parts per billion by volume) during this period. During the same period ozone levels were 8-77 ppbv. Monthly mean PAN levels were observed to be inversely correlated with monthly mean ozone levels

Screening for Neuroblastoma in the Northern Region of England Laboratory Aspects

Our pilot study for neuroblastoma screening started in 1986. The study has progressed through several phases, with use of several analytical methods to a procedure based primarily on the use of automated gas chromatography mass spectrometry. The northern region of England has a relatively static population of approximately 3.5 million, with an annual birth rate of 41,000. The region consists of 16 administrative health districts. In 4 years, we have screened 20,829 infants from four health districts. In this program, we screen all children at 6 months of age. A urine sample is collected on filter paper by a health visitor, either at the time of the infant's routine clinic visit or during the health visitor's follow-up visit at home. In the laboratory, the sample is dried and processed for analysis of homovanillic acid (HVA) and vanillylmandelic acid (VMA), using a benchtop Hewlett Packard gas chromatograph mass spectrometer. The results are related to the creatinine content of the urine. Using cut-off limits of 39 micrograms/mg of creatinine for HVA and 25 micrograms/mg of creatinine for VMA, 2,537 infants (12.2%) required a second paper sample and 527 infants (2.5%) were observed with a liquid urine collection. Of these, the conditions of nine infants with elevated levels of HVA or VMA were investigated clinically for the possible presence of neuroblastoma. Two infants were found to have neuroblastoma; the other seven showed no evidence of tumor. In addition, there were three children who, when screened at 6 months of age, had normal levels of HVA and VMA but in whom neuroblastoma subsequently developed.

Screening for Neuroblastoma in the Northern Region of England

Our pilot study for neuroblastoma screening started in 1986. The study has progressed through several phases, with use of several analytical methods to a procedure based primarily on the use of automated gas chromatography mass spectrometry. The northern region of England has a relatively static population of approximately 3.5 million, with an annual birth rate of 41,000. The region consists of 16 administrative health districts. In 4 years, we have screened 20,829 infants from four health districts. In this program, we screen all children at 6 months of age. A urine sample is collected on filter paper by a health visitor, either at the time of the infant's routine clinic visit or during the health visitor's follow-up visit at home. In the laboratory, the sample is dried and processed for analysis of homovanillic acid (HVA) and vanillylmandelic acid (VMA), using a benchtop Hewlett Packard gas chromatograph mass spectrometer. The results are related to the creatinine content of the urine. Using cut-off limits of 39 micrograms/mg of creatinine for HVA and 25 micrograms/mg of creatinine for VMA, 2,537 infants (12.2%) required a second paper sample and 527 infants (2.5%) were observed with a liquid urine collection. Of these, the conditions of nine infants with elevated levels of HVA or VMA were investigated clinically for the possible presence of neuroblastoma. Two infants were found to have neuroblastoma; the other seven showed no evidence of tumor. In addition, there were three children who, when screened at 6 months of age, had normal levels of HVA and VMA but in whom neuroblastoma subsequently developed.

Near-continuous measurement of hydrogen sulfide and carbonyl sulfide by an automatic gas chromatograph

An automatic gas chromatograph with a flame photometric detector that samples and analyzes hydrogen sulfide and carbonyl sulfide at 30-s intervals is described. Temperature programming was used to elute trace amounts of carbon disulfide present in each injection from a Supelpak-S column in a single peak at the end of 15-min runs. The system was used to study the high-temperature fuel-rich sulfur capture reactions of hydrogen sulfide and carbonyl sulfide with injected calcium oxide sorbent, necessitating the nearly continuous measurement of these gaseous sulfur species. The hydrogen sulfide concentration ranged from 300 ppm to 3000 ppm and the carbonyl sulfide from 30 ppm to 300 ppm. The system was also used to monitor sulfur dioxide levels under fuel lean conditions, and the results compared very closely with sulfur dioxide measurements made simultaneously with continuous UV sulfur dioxide instrumentation.

Alprazolam Levels and Response in Panic Disorder

Fifty-five young adult patients completed a study comparing alprazolam, propranolol, and placebo in the treatment of panic disorder and agoraphobia with panic attacks. Twenty completed 5 weeks of treatment with alprazolam. No concomitant psychological treatment was administered. Plasma alprazolam levels were determined at baseline and at the end of the trial by means of automated gas chromatography. These levels were significantly correlated with dose (p = 0.001). Dividing the data into quartiles based on alprazolam concentration, no direct, linear relationship was found between alprazolam levels and response (as defined by a criterion of zero panic attacks). However, analysis of the combined middle two quartiles versus the combined upper and lower quartiles showed a positive trend toward a curvilinear relationship; i.e., there was a greater response rate within the 18-62 ng/ml concentration range than in the combined 0-17 plus 63-107 ng/ml range, (chi 2 = 2.4; p = 0.12). The findings are very preliminary in nature. It remains to be seen if the results will reach significance with a large sample size and a more tightly controlled study design.

Surface measurements of carbon dioxide and methane at Alert during an Arctic haze event in April, 1986

Carbon dioxide (CO2) has been measured at Alert by grab flask sampling since 1975 as part of the World Meteorological Organization's Background Air Pollution Monitoring Program. Deviations of CO2 concentration from the mean annual cycle have previously been attributed to air masses arriving at Alert from the source regions of the industrialized parts of Europe and the Soviet Union. In situ measurements of ambient CO2 and methane (CH4) were made at Alert using an automated gas chromatograph, as part of the Arctic Haze Study during April 1986. The temporal behaviour of CO2 and CH4 during this period was found to be highly correlated with measurements of particulate sulphate and other atmospheric trace species of anthropogenic origin. Examination of calculated air mass back-trajectories provided further evidence that the observed short-term increases in CO2 and CH4 mixing ratios were due to long-range transport from anthropogenic source regions.

Sulfonium salts as derivatizing agents : 2. Determination of theophylline in plasma by automated gas chromatography

An automated gas chromatographic method for determination of theophylline in plasma is described. A novel feature of this assay is the use of triethylsulfonium hydroxide as an on-column alkylating agent. A simple extraction procedure together with automated sample injection and data processing has facilitated processing of large numbers of samples generated in pharmacokinetic studies. The between-run coefficient of variation was 2.2% at 5 μg/ml ( n=5) and 3.9% at 15 μg/ml ( n=6). Within-run coefficient of variation was 2.4% at 5 μg/ml ( n=9) and 3.3% at 15 μg/ml ( n=6). Accuracy was 105% at a concentration of 5 μg/ml and 102% at 15 μg/ml.

Microbial identification by gas chromatography

AbstractGas chromatography is rapidly being accepted as a valuable technique for the identification of microrganisms, as the speed of identification can be significantly greater than current biochemical techniques. The Health Department of the Institute of Naval Medicine has recently installed a fully automated gas chromatograph dedicated to rapid bacterial analysis particularly in the area of clinical microbiology. This paper describes the preparative and anlytical methods employed by the system and the results of preliminary studies.

Pan measurements in a forested area (Donon, France)

Abstract Continuous PAN measurements using a fully automated gas chromatograph have been performed since September 1986 in a forested area (Donon) in the east of France. The results showed a marked seasonal variation with a maximum observed in spring. A PAN concentration of 0.2 ppb can be considered as the background level of this region, while substantial PAN levels (1–2 ppb) were recorded during several transport episodes. One of them is analysed and discussed in detail.

Interactive and multi-sensory analysis of complex mixtures by an automated gas chromatography system

Interactive and multi-sensory analysis of complex mixtures by an automated gas chromatography system