Multichannel autosampler for Curie-point pyrolysis capillary gas chromatography

A multichannel autosampler which can automatically analyze up to 20 samples in sequence has been developed for on-line Curie-point pyrolysis – capillary GC. The results obtained from the system show that the analysis of thermally labile samples could be performed without either thermal degradation or reaction during the waiting time before the final pyrolysis. The reproducibilities of the relative peak areas and retention times of the characteristic pyrolysates of a tricomponent copolymer were significantly better than those obtained by manual sample manipulation.     

A splitless Curie point pyrolysis capillary inlet system for use with the adsorption wire technique of vapour analysis

Summary A splitless Curie point pyrolysis inlet system for capillary columns has been built using conventional packed column apparatus. This has enabled the adsorption wire analysis system, for the rapid collection and direct GC analysis of vapours, to be used with capillary columns. Use of the technique for detecting traces of hydrocarbon fuels in arson investigation is described, as are problems occurring in its use.     

Analysis of chemically modified polystyrenes with pyrolysis-capillary gas chromatography

Pyrolysis-capillary GC has been applied to the analysis of chemically derivatized polystyrenes. The reproducibility of the method and the influence of instrumentation has been discussed.     

Element-selective detection using capillary gas chromatography with atomic emission detection

Capillary GC coupled to an atomic emission detector (AED) provides a powerful new hyphenated technique for the separation and characterization of complex mixtures and compounds. The AED provides simultaneous and truly specific multi-element detection. The specificity of detection reduces the need for the complex sample pretreatment procedures which are necessary to reduce the interference from co-eluted substances which is experienced with detectors such as the FID and the ECD. A range of environmentally significant problems has been studied, including PCB analysis, the characterization of the reaction products of a novel waste treatment process, and the profiling of sulfur-containing species formed by the pyrolysis of various types of coal.     

Further applications for capillary gas chromatography in routine quantitative toxicological analyses

The use of capillary column gas chromatography for drug screening in forensic toxicology has become increasingly widespread. Screening procedures however are often lengthy and unsuitable for rapid confirmatory or quantitative applications. In order to develop a practical scheme for confirmatory/quantitative analysis, we have optimized a series of temperature profiles to allow the rapid quantitative determination of a wide range of acid/neutral and basic drugs in extracts from post mortem fluids and tissue. The appropriate profile is selected based on the retention index on a standard crosslinked methyl silicone column used to screen extracts. The use of a 5% phenyl methyl silicone phase allows complementary identification, and allows the separation of some pairs of compounds with identical retention indices in the screning procedure.     

Dynamic headspace capillary gas chromatography: A versatile analytical technique

The applicability of dynamic headspace analyses for viscous liquids and solid samples is demonstrated. Some comments on the usefulness of this technique for quantifying volatiles in polymeric matrices are made.     

The use of precolumns for solvent focusing in capillary column gas chromatography

In trace analysis by capillary GC it is often desirable to use larger than normal injection volumes to obtain sufficient sensitivity. This, however, results in a wider solvent peak and tailing, and may reduce column efficiency. This paper describes the use of a short length of a capillary precolumn coated with a stationary phase of polarity similar to that of the sample solvent and a film thickness greater than that of the analytical column; provided the right combination of polarities of injection solvent and liquid phases are used, the precolumn focuses the solvent band, thereby enabling the maximum injection volume to be increased without measurably reducing efficiency. Typical precolumn dimensions are 1 m length, 0.32 mm i.d., and 0.5 μm stationary phase film thickness. Using a precolumn increases the maximum injection volume up to 8 or 10 μl, or three times that appropriate for a conventional analytical column, with little or no loss in efficiency.     

Trace analysis of semi-volatile organic air pollutants using thick film silicone rubber traps with capillary gas chromatography

Established standard methods for analyzing semi-volatile pollutants by capillary gas chromatography are cumbersome, time-consuming, and expensive. With the longer term aim of replacing the sample preparation procedures with convenient concertrating and thermal desorption steps, thick film silicone rubber traps were constructed in a novel multi-channel configuration. Tests were performed to determine breakthrough volumes and thermal desorption characteristics for total transfer of the trap contents to a capillary column. Initial results are very promising.     

High-temperature separation with polymer-coated fiber in packed capillary gas chromatography

High-temperature gas chromatographic separation of several synthetic polymer mixtures with Dexsil-coated fiber-packed columns was studied. A bundle of heat-resistant filaments, Zylon, was longitudinally packed into a short metal capillary, followed by the conventional coating process with Dexsil 300 material. Prior to the packing process the metal capillary was deactivated by the formation of a silica layer. The typical size of the resulting column was 0.3-mm i.d., 0.5-mm o.d., 1-m length, and packed with about 170 filaments of the Dexsil-coated Zylon. The column temperature could be elevated up to 450°C owing to the good thermal stability of the fiber, Dexsil coating, and metal capillary; furthermore, this allowed the separation of low-volatile compounds to be studied.     

Evaluation of a radio frequency plasma for oxygen-selective detection in capillary gas chromatography

A radio frequency plasma detector for capillary GC has been modified for oxygen-selective detection. Purification of the plasma gas and purging of both ends of the discharge region with helium were crucial to minimizing oxygen background emission from impurities in the plasma. With a pure helium plasma, eluting hydrocarbons released oxygen from the discharge region resulting in interfering signals on the oxygen channel. These interfering signals were efficiently reduced by using a methane-doped (0. 15%) low power RF plasma (15 W) sustained in a high make-up flow (150 mL/min). With this plasma, a 10³:1 oxygen-to-carbon selectivity and a 100 pg oxygen/s detection limit were obtained. The detector was linear over three orders of magnitude. The detection system has been used to screen for oxygenated compounds in two environmental samples.     

A continuous liquid-liquid extraction system coupled on-line with capillary gas chromatography for environmental and ecotoxicological analysis

The applicability of a liquid-liquid extraction system which is coupled on-line with a capillary gas chromatograph was studied for environmental and ecotoxicological analyses. The optimized and automated system was used for the determination of apolar and rather non-volatile organic compounds in aqueous samples. Relevant aspects of sample introduction, phase separation and selection of extraction solvent are discussed. Three routine-tipe applications are described, viz. an improved method for the determination of hexachlorocyclohexanes in ground water and the determination of the so-called NCC-ether and ACC-ether in ecotoxicological studies. Depending on the application studied, the concentration levels varied from 0.1 to 6000 μg/I, using ECD and/or FID detection. Typical coefficients of variation obtained with the total extraction–GC procedure were 2–25%. The system was found to be rugged, it saves time compared with set-ups involving off-line liquid-liquid extraction and considerably reduces the manual work load.     

Analysis of antiepileptic drugs by capillary gas chromatography with on-column injection

A simple and quick gas chromatographic method has been developed for the determination of up to six commonly used antiepileptic drugs in human serum. The antiepileptics are isolated from serum by solid phase extraction on to a reversed phase sorbent and recovered with ethyl acetate as eluent. The ethyl acetate eluate is suitable for direct on-column injection on to a phenyl methyl siloxane capillary column; hydrogen is used as carrier gas and the compounds are separated with a two-ramp temperature program. Detection is by FID. The reproducibility of the method varies between 2 and 6% RSD, depending on the drug and the level analyzed; limits of detection were found to be 14–51 pg and minimum assayed concentrations in serum were between 14 and 51 ng/ml.     

An automated large volume on-column injection technique for capillary gas chromatography

Automated large volume (25-200 μl) on-column injections into a gas chromatograph with a capillary column were successfully performed by coupling a retention gap technique with an air actuated rotary valve. The linearity, injection precision, and carryover were evaluated. Slight boiling point discrimination was observed. This technique is compatible with commonly used chromatographic detectors (FID, ECD, MS) and conditions, while requiring very little instrument modification. The work is directed at the eventual reduction of manpower and turnaround time for sample collection and extraction, and Kuderna-Danish concentration when dealing with methods similar to EPA 625.     

Practical limitations of capillary gas chromatography

Glass capillary gas chromatography is a high resolution separation method which allows the qualitative and quantitative analysis of even complex mixtures, which may contain many components–also isomeric–in a wide range of volatilities, polarities and concentrations. The principal limitation of gas chromatographic application is given by an insufficient volatility of the species to be separated. Elevated temperatures have to be applied if the application range is to be extended and to achieve steep peak profiles, i.e. low detection limits at high resolution. The use of elevated temperatures is limited, of course, by the temperature stability of both the solvent (stationary liquid and support) and the solutes. The problems of trace analysis for low volatility compounds at high resolution and its limitational parameters regarding sampling, separation and detection are discussed. The applicability of glass capillary columns in this field is influenced by the following parameters: tailing behaviour; irreversible adsorption of polar and decomposition of unstable solutes; thermal stability of stationary liquid (including the support deactivation); separation efficiency and sample capacity (film thickness). Multidimensional gas chromatography using capillary columns coupled either with a packed or another capilllary column for preseparations may be applied with advantage in the analysis of complex mixtures.     

An improved method for steroid profile analysis using capillary gas chromatography

Summary Steroid conjugates are hydrolysed enzymatically using β-glucuronidase after extraction from urine using a solid phase extraction cartridge. After hydrolysis the free steroids are removed from the matrix, again utilising solid phase extraction. Derivatisation of the free hydroxyl groups using Hydrox-Sil AQ produces the respective TMS ethers which are extracted into hexane, in which solvent they are stable for many days. Capillary GC analysis with flame ionisation detection produces a profile of the steroids present in the sample. This technique is suitable for following changes in the urinary excretion profiles of patients undergoing investigation for a variety of steroid production-related diseases.