Sampling for gas chromatography

In this chapter, techniques for the extraction of volatile compounds from various matrices are described. Details are provided on the basic theory and applications of each technique with a focus on providing useful information to the analyst working on the analysis of volatile analytes from difficult matrices. Since the analytes are volatile, most of the techniques are geared toward preparation of samples for gas chromatography, although they are appropriate for many instrumental methods. The chapter is heavily referenced and the reader should refer to the appropriate references for more details on a particular technique or application. 

I. Ciucanu and R. Carpita, Per-O-methylation of neutral carbohydrates directly from aqueous samples for gas chromatography and mass spectrometry analysis, Anal. Chim. Acta, 585 (2007) 81-85. 

Kato, K. Yoshimura, Y. Ito, Y. Oka, H. Nakazawa, H. Preparation of samples for gas chromatography/mass spectrometry analysis of phthalate and adipate esters in plasma and beverages by steam distillation and extraction. AO AC Int. 2002, 85, 719. 

Figure 22-21 Injection valve for HPLC. Replaceable sample loop comes in various fixed-volume sizes. Similar valves can be used to inject gaseous samples for gas chromatography.

Time, Cost, and Equipment Analysis time can vary from several minutes for samples containing only a few constituents to more than an hour for more complex samples. Preliminary sample preparation may substantially increase the analysis time. Instrumentation for gas chromatography ranges in price from inexpensive (a few thousand dollars) to expensive (more than 50,000). The more expensive models are equipped for capillary columns and include a variety of injection options and more sophisticated detectors, such as a mass spectrometer. Packed columns typically cost 50- 200, and the cost of a capillary column is typically 200- 1000. 

Carrizo D, Grimalt JO (2006) Rapid and simplified method for the analysis of polychlor-onaphthalene congener distributions in environmental and human samples by gas chromatography coupled to negative ion chemical ionization mass spectrometry. J Chromatogr A 1118(2) 271-277... 

Gas chromatography is especially useful for gas-phase analysis of partial oxidation, hydrogenation, or hydroconversion products as in many cases a full carbon balance (educts, products, and all side products), in order to evaluate sample performance. As the detection and quantification of permanent gases such as N2, 02, CO, and C02 and also of higher boiling compounds are standard separation problems for gas chromatography, it is wise to employ the method regarding this problem. 

The sediment sample is allowed to dry in open air and then sieved. To 20g of the sample 20% distilled water is added for deactivation purposes and the excess water is then bound to active silica (Siloxid), so that a powdery consistency is obtained. The insecticides studied are extracted with petroleum ether (b.p. 30-60°C) in a Soxhlet apparatus. The extract is concentrated using the vacuum rotary evaporator and the coextractants are separated on a Celite oleum column. The petroleum ether eluate is then concentrated to a volume of 1ml and used for gas chromatography under the following conditions [10, 31-33],... 

Cotterill [119] used the soil extraction method devised by McKone [120] in which a 25g sample of soil was extracted with 50ml of methanol by shaking on a wrist-action shaker for lh. The resulting soil slurry was filtered through a Whatman No. 42 filter-paper. For gas chromatography, a 2ml... 

Macleod KE, Hanisch RC, Lewis RG. 1982. Evaluation of gel permeation chromatography for clean up of human adipose tissue samples for gas chromatographic-mass spectrometric analysis of pesticides and other chemicals. J Anal Toxicol 6(1) 38-40. 

For gas chromatography analysis, samples were spiked with 2-methyl-naphthalene as an internal standard. Samples were analyzed using a Shimadzu GC-17A series gas chromatograph equipped with RTX-5 column, 15 m (length) 0.25 mm (i.d.) and 0.25 pm (film thickness). The initial column temperature was 70 °C and temperature was increased at 20 °C min 300 °C, and column temperature was held for 13 min. Retention times R naphthalene, 3.2 min 2-methyl-naphthalene, internal standard, 4.09 min 1-tetralone, 4.7 min menadione, 5.68 min 1-naphthol, 5.7 min 4-hydroxy-1-tetralone, 6.1 min and 2-methy 1-4-hydroxy-1-tetralone, 6.18,6.27,6.3 and 6.4 min. 

Atrazine, alachlor and trifluralin were determined in the extracts of the samples by gas chromatography using a N-P detector. An EC detector was used for the determination of parathion, 2,4-D ester and the 2,4-D acid after esterification with diazomethane. Car-baryl and 1-naphthol were determined colorimetrically by the procedure of McDermott and DuVall (39). 

R. Zhao, S. Chu and X. Xu, Optimization of nonequilibrium liquid-phase microextraction for the determination of nitrobenzenes in aqueous samples by gas chromatography-electron capture detection. Analytical Sciences International Journal of the Japan Society for Analytical Chemistry, 2004, 20(4), 663-666. 

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