Capillary Column Inlet System for the Gas Chromatography of Biological Samples

Abstract

A glass injection system consisting of a packed precolumn and gasphase splitter has been developed for the introduction of derivatized biological samples on glass capillary columns. The precolumn provides complete sample evaporation before the splitter zone, traps contaminating nonvolatiles, and prevents decomposition or adsorption of components. In addition, a carrier gas control system is described that permits stable and repeatable adjustment of split ratio and capillary inlet pressure.

The linearity of the splitter has been established using a hydrocarbon mixture covering the range of methylene unit (MU) values in which the steroid derivatives are eluted.     

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.     

Pressure Capillary Spot-Test for the Detection of Pollutants in Crops,Vegetation and Environment

Abstract

A new, simple, sensitive and selective technique, pressure capillary spot test, has been developed for the detection and determination of pollutants containing amino, carbonyl, carboxylic or phenolic groups. The pressure has been reduced with the help of a suction pump and a capillary containing p-diemthylaminobenzaldehyde has been used as detector for the semi-quantitative determination of plant growth regulators, indoleacetic acids, in wheat shoots.     

Isolation and Determination of Volatile Organic Compounds from Water by Dynamic Purge-and-Trap Technique Coupled with Capillary Gas Chromatography

The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water.     

Utilization of Dual Phase Gas Diffusion FIA with a Mass Spectrometer as a Detector

Abstract

The coupling of dual phase gas diffusion flow injection analysis with mass spectrometry has been shown to be feasible. This combined technique offers a high degree of selectivity and sensitivity. This technique was developed to determine whether volatile mixed arsenic selenium hydrides are formed in dual phase gas diffusion flow injection analysis hydride generation.     

Determination of Airborne Nicotine by Automatic Two-Stage Thermal Desorption Gas Chromatography

Abstract

An automated two-stage thermal desorption technique has been developed for the determination of airborne nicotine. Pumped samples are collected on adsorbent tubes and analysed by capillary gas chromatography using flame ionisation detection. The preconcentration effect of the adsorbent compared to solvent trapping or solvent desorption methods permits shorter sampling times and precludes the need for a selective detector.

By use of a basic program all exposure volumes and component details are entered into a method run table and after analysis exposure levels are automatically calculated and printed in report form by the data handling system. Consequently a large throughput samples may be analysed automatically and efficiently with minimal analyst involvement or sample preparation.

The technique described was originally developed to sample airborne nicotine in workplace environments where tobacco is processed. Comparison between this technique and the standard NIOSH method for airborne nicotine is discussed.     

Determination of Trace Amounts of Organic Pollutants in the Yellow River by Capillary Column Gas Chromatography-Mass Spectrometry

Abstract

The trace organic pollutants in the Yellow River enriched by a solvent extraction method were pre-separated into four different fractions of fatty hydrocarbons, polycyclic aromatic hydrocarbons, polar compounds and organic acids and were analyzed by the use of combined capillary column gas chromatography-mass spectrometry. Using the combined techniques of relative retention value, mass spectra and mass chromatogram, more than 60 organic pollutants were identified, among which 16 fatty hydrocarbons and 6 polycyclic aromatic hydrocarbons which were quantitatively analyzed. The concentration range of fatty hydrocarbon was 5–800 ng/l, and that of polycyclic aromatic hydrocarbon was 0-90ng/l.     

Gas Chromatographic Analysis in the Synthesis of Poly (Ethylene Oxide) Dimethyl Ethers

ABSTRACT

Gas chromatography (GC) was used in the analysis of the synthesized oligomeric mixtures, involving poly(ethylene glycol)s, poly(ethylene oxide) monomethyl ethers, poly(ethylene oxide) dimethyl ethers and crown ethers. It was demonstrated that the samples could be successfully analyzed on the wide bore capillary column with cross-linked polar stationary phase (FFAP) without derivatization. An on-column injection technique is used to avoid possible sample distortion. Identification and quantitative analysis were achieved taking advantage of the GC homologues retention rule and the FID effective carbon number response rule, thus the limitations of some standard availability and purity problems were avoided. Much useful information such as average molecular weight, polydisperse distribution and so on were obtained by the established method, which is very important in the process monitoring and product quality control.     

A Comparative Study of Hydrodistillation and Hydrodistillation–Solvent Microextraction Methods for Identification of Volatile Components of Echinophora cinerea

A recently developed hydrodistillation–solvent microextraction (HD–SME) method coupled to gas chromatography–mass spectrometry (GC–MS) was applied to the analysis of volatile components of aerial parts of Echinophora cinerea (Boiss). By the use of a simplex optimization method, the effects of extraction time, sample weight and microdrop volume on the extraction efficiency of the method were optimized. In the optimized conditions, 3 µL of n-heptadecane was suspended in the headspace of 6 g of hydrodistillating sample, using a microsyringe. After 7 min, the solvent was retracted back into the syringe and directly injected into the GC–MS injection port. The HD–SME method was compared to a conventional hydrodistillation technique. In general, the extraction with HD–SME was relatively faster and required smaller amounts of sample. The microextraction method also showed some selectivity towards α-phellandrene and Z-β-ocimene monoterpenes. A precision better than 6.5% (expressed as relative standard deviation) was obtained for the method.

     

Membrane Focusing - A New Injection Method For Capillary Gas Chromatography

Abstract

The principles of a new sample focusing technique in capillary gas chromatography are described. A solidsorbent trapped sample is thermally released from the sample tube, transfered to a membrane chamber by a carrier gas and there retained by a gas separation membrane which is highly permeable to the carrier gas. After focusing in the membrane chamber the sample is brane chamber geometry to increase the membrane surface and thereby the carrier gas flow is promising too.

The major advantage of a membrane focusing system as compared to the cryofocusing technique would be no need for a cooling agent. Such a system would be favourable for hydrocarbon analyses at remote sites.     

Evaluation of Octanol-Water Partition Coefficients Using Capillary Gas Chromatography With Cold On-Column Injection

Abstract

A general procedure is described for the determination of the octanol-water partition coefficients (log P) of very lipophilic compounds by the shake flask method, employing the analytical technique of capillary gas chromatography with cold on-column injection. The solute and an internal reference with a known log P value are partitioned between the layers of an octanol-water mixture and their relative concentrations are determined by analysis of each phase, using highly standardized chromatographic conditions. The overall method is demonstrated to be convenient, reproducible, and useful for the determination of the partition coefficients of a wide variety of compounds with log P values as high as 5.7.     

Enzyme Urea Biosensor Based on a Modified Potentiometric PVC-Nonactin Membrane Electrode for Assay of Urea in Blood

Abstract

The developed potentiometric urea biosensor is based on a modified PVC-nonactin NH₃ -sensitive gas electrode. Membrane resistance has been optimised by incorporating lipophilic salt. The coefficient of variation for the standard urea solution is 2.45. The sensor performance has been compared with a photometric method for blood samples.     

Electron Capture Gas Chromatography of Tertiary Amines After a Demethylation Reaction to Secondary Amines

Abstract

A gas chromatographic method for the determination of tertiary amines in micro- and nanogram amounts is presented. The tertiary amine is reacted with ethyl chloroformate to form a urethan, which is cleaved to a secondary amine. This is transformed to heptafluoro-butyramide, which makes quantitative determination with electron capture detection possible. The yields of the secondary amines for two tertiary amines were 60 and 75%. By use of internal standard technique in the entire reaction recoveries of 97.6 ± 2.2% at the 100 μg level and 100 ± 4% at the 200 ng level were obtained.     

Gas Chromatography of δ1-Tetrahydrocannabinol

Abstract

Quantitative gas chromatography of small amounts of δ¹ - tetrahydrocannabinol has been demonstrated on a variety of silicone columns. Retention data in the form of methylene unit values were obtained on these columns.     

Analysis of Malodorous Sulfur Gases and Volatile Organometalloid Compounds in Landfill Gas Emissions Using Capillary Gas Chromatography with Programmed Temperature Vaporization Injection and Atomic Emission Detection

Volatile compounds containing Group V and Group VI elements in landfill gases are of concern as a source of toxic pollutants and unpleasant odors. Conventional analytical techniques for these compounds e.g. ICP-MS, ICP-AES are complicated, expensive and time consuming. The use of a simple programmed temperature vaporization injection (PTV) technique coupled to gas chromatography with atomic emission detection (GC-AED) has been successfully demonstrated to identify compounds containing arsenic, antimony, and sulfur in landfill gas. With an adapted PTV injection system (using a combination of a ten-port and a six-port Valco valves), problems associated with AED discharge tube damage due to high carrier gas flow rate during sample loading can be overcome. The gas samples generated from both a laboratory biowaste digester and a domestic landfill site were characterized using these techniques. Large sample gas volumes were adsorbed onto a cooled sorbent trap containing Porapak Q, followed by rapid liberation onto a porous layer open tubular column (PLOT) using programmed thermal desorption. Arsenic and antimony were also detected in the landfill leachate collected from the same landfill site using hydride generation-atomic absorption spectrometry (Hy-AAS). The efficiency of different traps has also been compared.     

Abstracts

Abstract

The developed potentiometric urea biosensor is based on a modified PVC-nonactin NH₃-sensitive gas electrode. Membrane resistance has been optimised by incorporating lipophilic salt. The coefficient of variation for the standard urea solution is 2.45. The sensor performance has been compared with a photometric method for blood samples.     

Determination of Nonpolar Chlorinated Hydrocarbons and PCB in Microsamples

Abstract

Analysis of small samples of fish eggs, rat brain sections and aquatic macro-invertebrates for 78 PCB congeners, hexachlorobenzene, octachlorostyrene, p, p′-DDE and mirex is described. With a gas chromatograph equipped with an Apiezon L coated glass capillary and electron capture detector capable of determining 10 ng/ml of analyte in hexane, a 10 mg sample may be analyzed with a precision of better than ±5% relative standard deviation.     

Determination of Selected Persistent Organochlorine Pollutants in Human Serum by Solid-phase Disk Extraction and Dual-Column Capillary Gas Chromatography with Electron Capture Detection

Abstract

An improved clean-up method by solid-phase disk extraction was developed to isolate and concentrate trace levels of POPs (persistent organochlorine pollutants) in human serum prior to gas chromatography with electron capture detection on two different capillary columns, providing an improved selectivity. An Empore^TM C₁₈ bonded silica extraction disk cartridge is used for the initial extraction and enrichment of the analytes. Subsequent clean-up is achieved by concentrated sulphuric acid and silica gel adsorption chromatography. Recoveries for selected POPs are ranging from 62 to 74% and a good reproducibility (RSD < 14%) is demonstrated. Human samples analysed under these conditions, show a similar relative concentration profile.     

Isolation,Concentration and Subsequent Analysis by Capillary Gas Chromatography of Trace Amounts of Organophosphorus Compounds from Aqueous Samples

Abstract

Trace amounts (ppb or less) of phosphorus containing compounds present in aqueous samples are adsorbed on XAD-4 and subsequently eluted by means of ethyl acetate. The solvent and the eluted compounds are evaporated and swept over a Tenax-GC tube. This gas stripping method traps the phosphorus containing compounds together with only a small amount of the solvent whereas the water entrapped in the XAD step is removed simultaneously. The compounds are desorbed from the Tenax-GC tube and injected into the gas chromatograph using the combination of thermal desorption, cold trapping and flash heating. The subsequent analysis is carried out on a capillary column and the compounds are detected by means of a flame photometric detector. The various steps of the analytical procedure are discussed, including the recoveries of the different compounds studied and some instrumental aspects.     

Analysis of organic pollutants in sewage by supercritical fluid extraction

Summary Analytical methods have been developed for the determination of organic pollutants of intermediate polarity in sewage. Water samples are first passed through a solid phase adsorption cartridge. The analytes are then extracted from the absorbent with supercritical CO₂ into a small volume of trapping solvent. Finally, the extracts are analyzed directly by capillary gas chromatography and gas chromatography-mass spectrometer. The various parameters (pressure, temperature, type and concentration of modifiers, trapping solvent, flow rate and volume of supercritical fluid and equilibrium time) influencing the efficiency of extraction were studied. Extraction efficiencies for the test compounds are >70%, and relative standard deviations are <4.6% (n=3). The methods established were applied to the analysis of sewage at the Lanzhou Wastewater Treatment Plant, China. 66 organic pollutants were detected, of which 15 compounds appeared in the list of priority pollutants suggested by the US EPA.