A versatile cryo-focussing flow switching gas chromatography inlet for trace analysis of intractable compounds.

Peter Apps, Lesego Mmualefe

Index: J. Chromatogr. A. 1257 , 171-88, (2012)

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Abstract

A wide variety of samples that can be analysed by gas chromatography do not lend themselves to the usual preparation of solvent extracts for split-splitless injections, and are best handled by purge and trap or equilibrium headspace sampling. A cryo-focussing, flow switching gas chromatography inlet system that handles different types of sample without the need for hardware changes has been prototyped. It provides excellent repeatability and linearity with liquid injections, purge and trap, and equilibrium headspace samples, in both split and splitless modes. The performance of the system was tested with sub-nanogram quantities of challenging analytes such as free carboxylic acids, alcohols, diols, phenols and aldehydes, and volatiles purged from contaminated soil, mammal faeces, a pesticide formulation, and a spice. Repeatability RSDs for peak areas were consistently below 11% and repeatabilities of retention times below 0.05%, independently of sample type (liquid or gas phase) and nature or quantity of compound. Regression coefficients of peak areas vs. quantity were typically ≥ 0.999 over two orders of magnitude ranges extending down to below 0.01 ng, also independently of sample and analyte. Limits of quantitation were robustly below 0.1-0.2 ng. Peak shapes and resolution are the same with use of the cryo-trap and flow switch as they are with conventional injections. Performance is robust to flow rate and, for most compounds, to trapping and desorption temperature. The cryo-trapping flow switching inlet's performance parameters match those of other sample introduction systems, and are achieved with sub-nanogram quantities of intractable analytes.Copyright © 2012 Elsevier B.V. All rights reserved.