Gas Chromatography

1.4.3 Analytical methods

Gas chromatography is the most commonly applied method for the analysis of trace components in human breath. In gas chromatography the compounds are vaporized and separated according to their boiling points. Flame ionization detection (FID) is one of the most common detection methods, as GC-FID exhibits high sensitivity, large linear response range and low noise. The drawback of GC-FID is the identification, which is retention time based only. Retention times in GC are poorly reproducible long-term and between different systems as very subtle differences in the chromatographic system may cause large retention time deviations resulting in insufficient accuracy. In contrast to the GC-FID, gas chromatography coupled to

Each analyte molecule exhibits a unique fragmentation pattern which offers positive confirmation of the peak identity. Despite its widespread use in the area of breath analysis, disadvantages in GC-MS include the need for preconcentration and that it cannot be performed in real time. Other MS-techniques have also been successfully applied, such as selected ion flow tube-mass spectrometry (SIFT-MS) and proton-transfer reaction-mass spectrometry (PTR-MS). PTR-MS is particularly suited to online and multiple measurements and is advantageous for complex gas mixtures such as breath samples as it does not require any preconcentration. However, the identification of compounds is somewhat limited by the fact that characterization is based only on the m/z ratio. SIFT-MS can be used for real time quantification of several trace gases in breath and it is possible to perform direct analysis of single breaths. Real time analysis can also be performed by using analytical methods based such as laser spectrometry and chemical sensors [Kim 2012]. A custom built breath sampler, connected to canned air and utilizing a heater to avoid condensation of the breath will be used in combination with thermal desorption tubes (Carbotrap 300) and a Perkin Elmer GC-MS system with an