Measurement of Gaseous composition of human breath: Breath analysis is a potential innovative field of medicine as well as medical instrumentation, which tenders noninvasive, real-time, as well as point-of-care (POC) disease diagnostics and monitor of metabolic status. The detection of abundant breath biomarkers has been done and the quantification of the identified biomarkers have also been done till date by the usage of GC-MS technique. Modern advancements in laser spectroscopic techniques as well as laser sources have moved breath analysis to newer levels, shifting from laboratory research to commercial reality. Laser spectroscopic detection techniques are not only highly-sensitive and highly-selective, they are as consistently presented by the MS-based techniques, and also possesses the advantageous aspects of near real-time response, low instrument costs, as well as POC function.
A key technique principally applied for breath gas analysis is gas chromatography-mass spectrometry (GC-MS). This technique includes a routine detection sensitivity of ppb to ppt and has the ability of analyzing multiple compounds in a simultaneous and selective way; yet, GC-MS needs complex procedures for sample collection as well as pre-concentration and also possesses high instrument costs.
Apart from the usual GC-MS techniques, a comparatively fresh technique, proton transfer reaction mass spectrometry (PTR-MS), finds usage for breath profiling. Vacuum-free ion mobility spectroscopy (IMS) mixed with a multi-capillary column has been utilized for identification of metabolites and bacteria in human breath as well. IMS is slightly less sensitive as compared GC-MS and PTR-MS and has much potential for the development of a hand-held breath device. By comparing, selected ion flow tube mass spectrometry (SIFT-MS), also belonging to the MS-based category, functions remarkably well in clinical breath analysis; on-line breath analysis of several breath compounds under a variety of physiological conditions have been conducted in clinics with actual human breath. Breath analysis is also conducted by the usage pf electrical sensors, that are moderately cheap and smaller in size, however they possess low detection selectivity and need recurrent calibrations.
Fresh advancements in high-sensitivity, high-selectivity laser spectroscopic techniques as well as laser sources have made it possible for breath analysis to be advanced from the MS-based, time-consuming, laboratory studies to laser-based, real-time, clinical testing. Some of the techniques used nowadays are the tunable diode laser absorption spectroscopy (TDLAS), cavity ringdown spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), cavity enhanced absorption spectroscopy (CEAS) , cavity leak-out absorption spectroscopy (CALOS), photoacoustic spectroscopy (PAS) , quartz-enhanced photoacoustic spectroscopy (QEPAS) and optical frequency comb cavity-enhanced absorption spectroscopy (OFC-CEAS).