A new configuration for coupling purge-and-trap/cryogenic focusing/capillary column gas chromatography with splitless injection mode

A new configuration for coupling a purge-and-trap unit to a capillary column gas chromatograph via a cryogenic focusing interface has been developed. In this configuration, the precolumn of the cryogenic focusing interface was inserted through the septum of a split/splitless injection port where it served as both sample transfer and carrier gas supply lines. The injection port of the gas chromatograph was modified by plugging the carrier gas and the septum purge lines. This configuration allowed for the desorption of analytes at high flow rates while maintaining low, analytical-column flow rates which are necessary for optimum capillary column operation. The capillary column flow rate is still controlled by the column backpressure regulator. Chromatograms of purgeable aromatics exhibited improved resolution, especially for early eluting components compared to those obtained by direct liquid injection using the normal splitless injection mode. Quantitative sample transfer to the analytical column afforded excellent linearity and reproducibility of compounds studied.     

Possibilities of dynamic headspace analysis coupled with capillary GC for the investigation of solid samples

The advantages of the dynamic headspace method for the analysis of solid samples, as compared with the static head space method, are discussed. Examples of dynamic headspace analyses are given to illustrate its possibilities.     

Sensitive determination of styrene and related compounds in human body fluids by headspace capillary gas chromatography with cryogenic oven trapping

Summary A simple and sensitive method is presented for determination of styrene, toluene, ethylbenzene, isopropylbenzene andn-propylbenzene in human body fluids by capillary gas chromatography (GC) with cryogenic oven trapping. After heating a blood or urine sample containing each compound andp-diethylbenzene (internal standard, IS) in a 7.0-mL vial at 60°C for 20 min, 5 mL of headspace vapor was drawn into a glass syringe and injected into a GC. All vapor was introduced into an Rtx-Volatile middle bore capillary column in splitless mode at oven temperature of 20°C to trap entire analytes, and the oven temperature then programmed to 280°C for GC measurements by flame ionization detection. The present conditions gave sharp peaks of each compound and IS, and low background noises for whole blood or urine samples.     

Cryofocusing in the combination of gas chromatography with equilibrium headspace sampling

Summary When headspace gas chromatography utilizing capillary columns is used for trace analysis, sample enrichment is often needed. This involves splitless sample injection of fairly large gas volumes and relatively long sampling times. As a result of this, the band of the sample vapor may be too large causing peak distortion and poor resolution. This problem can be easily overcome by the use of cryogenic trapping. While this can be accomplished by cooling the whole column to subambient temperature during sample introduction, a more convenient way is to utilize part of the first coil of the capillary column as a cryogenic trap.The paper discusses the theoretical background and instrumentation of cryogenic trapping and demonstrates the possibilities through a number of examples.Enlarged text of a paper presented at the 37th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Atlantic City, NJ, March 10–14, 1986.     

A very thick film open-tubular trap for headspace capillary gas chromatography

Summary An open-tubular trap with a very thick film was studied for “full on-line” headspace capillary gas chromatography, and was used as an enrichment trap for headspace sampling. The preparation of the open-tubular column with up to an 80 μm thick film, by combining both static and dynamic coating, is described in detail. The break-through volume for the open-tubular trap of different film thickness, as the loading capacity for HS sampling, does not increase linearly in proportion to the film thickness. A study of the difference between a packed adsorbent trap and an open-tubular trap shows that HS capillary GC with open-tubular trap loses less of the retention capacity, has better resolution ability and higher recovery. By independently and rapidly heating the open-tubular trap, the GC peaks may have higher resolution. Examples of successful analyses, by the opentubular trap with “full on-line” HS capillary GC, include trace aromatic hydrocarbon (1 ppm-100 ppm) in polybutadiene-styrene rubber and trace alcohol and acrylic esters (10 ppm–1000 ppm) in polyacrylate hydrous emulsion.     

Stationary-phase focusing in capillary gas-liquid chromatography: Enhancement of the maximum permissible sample size

Equations have been derived to predict the extent to which the sample size may be increased, without decreasing the column performance, by stationary-phase focusing at sub-ambient temperatures. Under favorable circumstances the sample size may be enhanced several hundredfold.     

Analysis of headspace samples using off-line sorbent trapping coupled with automated thermal desorption and splitless injection onto a cryogenically cooled wide bore capillary column

Gas chromatographic equipment and procedures are described for automated splitless injection of pseudo-static headspace samples collected externally onto a sorbent trap. The GC microprocessor controls, in sequence, carrier gas backflushing of the sorbent trap for water removal, splitless thermal desorption into a cryogenically cooled wide bore (0.53 mm i. d.) capillary column and oven temperature programming. The method has been routinely applied for profiling the mid-to-high boiling compounds (bp 80–225°C) in the headspace of a variety of foods and beverages. Method criteria, advantages and limitations are discussed. FID and NPD chromatograms for brewed coffee and peanut butter volatiles are presented as typical examples.     

Review: The usefulness of the headspace analysis-gas chromatography technique for the investigation of solid samples

The scope of the headspace sampling technique for the analysis of solid samples is discussed, and the static and the dynamic headspace methods compared. Theoretical aspects relating to quantification are discussed. The paper considers both instrumental requirements and applications.     

Multiple headspace extraction—A procedure for eliminating the influence of the sample matrix in quantitative headspace,gas chromatography

Summary A stepwise gas extraction procedure is described for the quantitative gas chromatographic analysis of volatile compounds in solid and liquid samples. This procedure is a modification of the usual headspace analysis and can be carried out with the same equipment, provided a pressure and time controlled sampling system is used. This procedure is called Multiple Headspace Extraction (MHE) therefore. This method has first been developed for the analysis of monomers in polymers and residual solvents in printed films, but it is shown that can be applied to various other sample types also including even liquid samples.Dedicated to L. S. Ettre on the occasion of his 60th birthday.     

Interlaboratory comparison to evaluate a standardized calibration procedure for the headspace analysis of aromatic solvents in blood

The determination of volatile organic compounds in blood by headspace gas chromatography is one of the central and long-established analytical techniques in occupational medical biomonitoring. Nevertheless, the relatively low success rate in intercomparison programs shows that the headspace technique is insufficiently standardized. A critical stage of the analytical procedure seems to be the preparation of calibration standards in biological matrices. As part of an extensive interlaboratory comparison by the Analyses of Hazardous Substances in Biological Materials working group of the DFG Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, three typical procedures were compared with one another using typical aromatic solvents as an example. The best correlations between the participating laboratories and the best results for the analyses of samples from interlaboratory comparisons were obtained when highly concentrated stock solutions of the aromatic compounds in ethanol were first diluted with physiological saline and then used for spiking horse blood in headspace vials. This procedure can be easily standardized and is therefore recommended by the Analyses of Hazardous Substances in Biological Materials working group for the preparation of headspace calibration standards for aromatic compounds.Dr. Regine Heinrich-Ramm, our highly valued colleague, died in 2002From the Analyses of Hazardous Substances in Biological Materials working group of the Analytical Chemistry Group (Chair: J. Angerer, Erlangen) of the DFG Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (Chair: H. Greim, Weihenstephan)     

Design of a microprocessor-controlled automated injection system for the analysis of gas phase cigarette smoke using glass capillary columns

An automatic injection system for the analysis of gas phase smoke has been designed and evaluated using the microprocessor-controlled Hewlett-Packard 5830 gas chromatograph. The cryogenic preconcentration trap was constructed from relatively inexpensive and readily available materials. It was determined that the use of the preconcentration trap, as opposed to condensing the smoke on the head of the cold (-50°C) chromatographic column, significantly enhanced the resolution of the more volatile gas phase components. Data are presented which illustrate the injection system characteristics. In addition, chromatograms of gas phase smoke are presented which demonstrate the effectiveness of this technique.     

Use of headspace capillary GC to study the development of volatile compounds in fresh fruit

The composition of volatile compounds produced by fruit during growth and post-harvest storage and ripening has been studied and the different headspace methods compared. Static and dynamic headspace sampling have been compared and evaluated according to their capacity to collect and concentrate volatiles from the atmosphere surrounding the fruits, and FID, MSD, and organoleptic detection have been compared. The results emphasize that the headspace sampling procedure selected is crucial to the performance of subsequent analysis.     

Headspace methods for volatile components of grapefruit juice

Summary Static headspace, dynamic headspace (DHS) and strip/trap methods were evaluated with grapefruit juice volatiles and an aqueous model system of selected grapefruit volatile flavour components, to select the best method for the isolation of volatile components for subsequent GC analysis.Recoveries were calculated for these methods in the concentration range 0.01–10gml^–1 and compared. Analyte trapping followed by thermal desorption was performed with Tenax TA traps which gave good results in terms of very low blanks. DHS analysis gave the best results in terms of recovery efficiency and, if adequately combined with a simultaneous steam distillation/solvent extraction method, is the most suitable for the qualitative and quantitative investigation of grapefruit juice volatiles, and it might be extended to other fruit juices or liquid foods.     

Comparison of two systems for sample preparation and injection by dynamic headspace GC analysis

The performance of two commercially available systems employing dynamic headspace techniques for collection, enrichment, and injection of volatile compounds has been compared by GC analysis of test mixtures and dairy products. For technical reasons, it has not been possible to crate identical sorbent materials for both kinds of trap were not available, the most similar adsorbent available were chosen. The total quantity of volatile compounds from a test mixture at the column head was calculated using a theoretical model which enables comparable working conditions to be obtained. Under these circumstances special attention was paid to the repeatability of the data obtained from a test mixture in order to ensure reliable results in quantitative analysis. Significant differences in repeatability between the two systems seemed to originate from their distinctly different technical designs. A qualitative comparison of the systems has been performed using a sample of Swiss cheese. On the basis of the results obtained the systems have been dedicated to different applications in the laboratory of the FAM.     

Methodological aspects of headspace SPME: Application of the retention index system

The applicability of the retention index system to hcadspacc solid phase microextraxtion (HS–SPME) was investigated. In headspace SPME, the two equilibria gas phase/matrix and fiber coating/gas phase have to he considered. In this paper the equilibrium fiber coating/gas phase is discussed separately to characterize it more detailed and to investigate several methodical aspects. Therefore, the different distribution constants K_fiber/gas of n-alkanes, which were used for reference compounds, were related to their Kováts retention indices. The validity of the derived linear relationship log K_fiber/gas versus retention index I is demonstrated for various examples. This relation is helpful for the assessment of distribution constants of substances not available and for the choice of a suitable fiber coating. Furthermore, quantification of analytes in the gas phase can be done without authentic substances.     

Modified capillary GC/MS system enabling dynamic headspace sampling with on-line cryofocusing and cold on-column injection of liquid samples

The paper describes a capillary GC/MS hardware arrangement allowong either:

• (a) on-line injection of sample of gases and vapors coming from dynamic headspace or purg & trap samplers and their subsequent cryofocusing/thermal desorption prior to the analytical capillary column (first column):
• (b) direct injection of liquid samples through a cold on-column injector into a second analytical column (counted in series with the first).

Chromatographic profiles of acacia honey aromas provide condirmation of the suitability of this system.