Assessment of a combined gas chromatography mass spectrometer sensor system for detecting biologically relevant volatile compounds

Abstract

There have been a number of studies in which metal oxide sensors (MOS) have replaced conventional analytical detectors in gas chromatography systems. However, despite the use of these instruments in a range of applications including breath research the sensor responses (i.e. resistance changes w.r.t. concentration of VCs) remain largely unreported. This paper addresses that issue by comparing the response of a metal oxide sensor directly with a mass spectrometer (MS), whereby both detectors are interfaced to the same GC column using an s-swafer.
 It was demonstrated that the sensitivity of an in-house fabricated ZnO/ SnO2 thick film MOS was superior to a modern MS for the detection of a wide range of volatile compounds (VCs) of different functionalities and masses. Better techniques for detection and quantification of these VCs is valuable, as many of these compounds are commonly reported throughout the scientific literature. This is also the first published report of a combined GC-MS sensor system. These 2 different detector technologies when combined, should enhance discriminatory abilities to aid disease diagnoses using volatiles from e.g. breath, and bodily fluids. 
 29 chemical standards have been tested using solid phase micro-extraction; 25 of these compounds are found on human breath. In all but 2 instances the sensor exhibited the same or superior limit of detection compared to the MS.
 12 stool samples from healthy participants were analysed, the sensor detected, on average 1.6 peaks more per sample than the MS. Similarly analysing the headspace of E. coli broth cultures the sensor detected 6.9 more peaks per sample versus the MS. This greater sensitivity is primarily a function of the superior limits of detection of the metal oxide sensor. This shows that systems based on the combination of chromatography systems with solid state sensors shows promise for a range of applications.

Selectivity in trace gas sensing: recent developments, challenges, and future perspectives

“…228,229 GC-MS technique has been widely used to detect trace gases, VOCs, trace amounts of chemicals since its discovery and shows high selectivity up to ppb level. 230–232 Recent advanced mass spectrometric techniques like GC-MS and selective ion flow tube-mass spectrometry (SIFT-MS) or selected ion-monitoring mass spectrometry (SIM-MS) are widely used for their specificity, selectivity, and sensitivity for gas sensing. However, these techniques are suffered from complicated instrumentation, time-consuming measurement, non-compact, and expensiveness.…”

Hyphenated Mass Spectrometry versus Real-Time Mass Spectrometry Techniques for the Detection of Volatile Compounds from the Human Body

“…A Clarus 500 GC-MS (PerkinElmer, Inc., Gaithersburg, MD, USA) with a single quadrupole detector was used for all of the samples with the GC output split by S-Swafer technology (PerkinElmer, Inc., Gaithersburg, MD, USA), with 50% going to the MS, and 50% going to the MOS sensor. The full assessment of this novel analytical instrument is described elsewhere [ 49 ]. When tested to 29 standards across a range of functional groups and masses, 23 of these compounds showed that the MOS sensor had equal or superior sensitivity to MS.…”

“…Similarly, when tested with the headspace of stool samples and bacterial cultures, the MOS detected more peaks on average than the MS. The enhanced sensitivity of MOS combined with the qualitative data from the MS showed that this instrument has the potential to differentiate samples into clinically relevant groups while also providing metabolic insights [ 49 ].…”

Application of a solid-phase microextraction-gas chromatography-mass spectrometry/metal oxide sensor system for detection of antibiotic susceptibility in urinary tract infection-causing Escherichia coli – A proof of principle study

“…Wiesner et al [10] reported that metal oxide sensors (MOS) had potential use in the faster detection of antibiotic susceptibility. In previous work the combined GC-MS/MOS system showed the potential to detect VOCs in several matrices, thus combining the high sensitivity of MOS with the identification of specific VOCs by the mass spectrometer [17]. The analysis of headspace above E. coli cultures showed more peaks detected with the MOS than the MS detector [17].…”

“…In previous work the combined GC-MS/MOS system showed the potential to detect VOCs in several matrices, thus combining the high sensitivity of MOS with the identification of specific VOCs by the mass spectrometer [17]. The analysis of headspace above E. coli cultures showed more peaks detected with the MOS than the MS detector [17]. In addition the MOS sensor was more sensitive than the MS detector when used for the detection of a mixture of 29 standard VOCs.…”