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

© 2017 IOP Publishing Ltd. 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 two different detector technologies when combined, should enhance discriminatory abilities to aid disease diagnoses using volatiles from e.g. breath, and bodily fluids. Twenty-nine chemical standards have been tested using solid phase micro-extraction; 25 of these compounds are found on human breath. In all but two instances the sensor exhibited the same or superior limit of detection compared to the MS. Twelve 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

Uso da Microcromatografia Gasosa no Estudo da Evolução do Gás CO2 no Processo de Destilação Laboratorial de Petróleo

O petróleo ainda continua sendo a maior fonte de energia não renovável do planeta. No seu estado bruto tem pouca utilidade. No entanto, seus derivados apresentam alto valor econômico. Nas etapas de processamento primário do petróleo alguns compostos de ocorrência natural são indesejáveis, como os ácidos naftênicos, resinas, asfaltenos, compostos sulfurados e metálicos. O poder corrosivo dos ácidos naftênicos preocupa as indústrias petrolíferas devido ao prejuízo causado nas tubulações e refinarias. Estudos recentes indicam que uma parcela desses ácidos quando submetidos a elevadas temperaturas (>280°C) pode sofrer reações de descarboxilação e degradação térmica, originando dióxido de carbono (CO2) e ácidos de cadeias menores como produtos de degradação. Os ácidos de cadeias menores juntamente com os ácidos naftênicos que se mantiveram preservados são corrosivos e o CO2 ao entrar em contato com água forma o ácido carbônico (H2CO3), podendo contribuir nas taxas de corrosão nos equipamentos do refino. Assim, o presente trabalho consistiu no desenvolvimento de uma metodologia para quantificação online do CO2 liberado no processo de destilação de petróleo. A metodologia desenvolvida foi baseada na técnica de microcromatografia gasosa. Os dados quantitativos de concentração de CO2 gerados pela microcromatografia foram relacionados com os valores de temperaturas de destilação, obtendo-se assim uma variação na concentração de CO2 de acordo com a temperatura de destilação do óleo. Com os resultados obtidos observou-se que para todos os petróleos destilados houve uma tendência na formação do gás CO2 partir de temperaturas superiores a 200°C. Na tentativa de elucidar a possível origem deste gás, supôs um mecanismo de descarboxilação para tais ácido

The detection of trace volatiles from complex matrices using gas chromatography mass spectrometry (GCMS) techniques and selected ion flow tube mass spectrometry (SIFT-MS) assessment of volatiles produced from nitric oxide producing smart dressings

Volatile compounds (VCs) hold the potential to diagnose and monitor disease states in a cost effective, rapid, and most importantly non-invasive manner. Gas chromatography mass spectrometry (GC-MS) has been in use since the 1960s and remains the gold standard for qualitative VC analysis. Within this thesis three novel methods and/or utilisations of mass spectrometry are described. Chapter 2 describes and benchmarks a metal oxide sensor (MOS) coupled to a standard GC-MS instrument. Testing this system to the headspace of 12 stool samples the sensor detected a mean 1.6 more peaks per sample then the MS. This superior sensitivity exhibited by the MOS sensor should allow for greater discriminatory abilities to differentiate samples into clinically relevant groups. It has become increasingly important to qualitatively and quantitatively assess the VCs for use in monitoring health. Chapter 3 describes a novel method for the quantification of VCs from the headspace of stool samples analysed using GC-MSis presented. Using 13C labelled carbon compounds as internal standards a method has been designed which quantifies the compounds withinin the stool; 15 compounds were quantified. The EDX110 dressing has been developed by Edixomed Ltd; uses hydrogel technology to generate nitric oxide (NO) to enhance wound healing. A series of experiments first allowed for the development of a robust and reproducible method of real-time quantification. The effect of pH was assessed using citric acid buffered with sodium citrate, pH values3, 3.6, 4.2, 4.8, 5.4, and 6.2 were all analysed. NO production showed an inverse correlation; pH 3 producing 81 μg of NO and pH 6.2 only producing 7μg. With the exception of pH 3 HONO and NO2 remained relatively consistent across the pH values with a median 3 and 0.9μg respectively

Gas Flows in Microsystems

International audienc

Gas Chromatographic Microsystems for Airborne and Aqueous Volatile Organic Compound Determinations

New technologies offering sensitive, selective, and near-real-time identification and quantification of the individual components of complex mixtures of volatile and semi-volatile organic compounds (S/VOCs) are greatly needed in applications such as personal (worker) exposure assessment, air and water pollution monitoring, disease diagnosis, and homeland security. This dissertation describes the characterization of two prototype instruments containing core gas chromatographic microsystems (µGCs); the development and characterization of a microscale vapor extractor (µVE), and its integration with a µGC; and the development of adsorbent materials providing selective preconcentration of polar S/VOCs for use in certain µGC applications. Following a review of the background and significance of the research (Chapter 1), this dissertation then describes the design, modeling, and preliminary characterization of the µVE, which is a passive device containing microchannels and a polymer membrane that transfers dissolved VOCs from aqueous samples passed through the device to the gas phase for analysis by a downstream µGC (Chapter 2). In a proof-of-concept experiment, a hybrid µVE-µGC microsystem extracted four VOCs from a 700 µL sample of synthetic urine in 3.5 min, and then separated, identified, and quantified each VOC in ~80 sec with a projected detection limit as low as 660 parts-per-billion. The hybrid μVE-μGC microsystem may eventually permit rapid field/clinical analyses of water contaminants and urinary biomarkers of exposure and disease. Chapters 3 and 4 describe prototype µGC instruments that are referred to as Personal Exposure Monitoring Microsystems (PEMM-1 and PEMM-2, respectively). PEMM-1 is a laptop-controlled, AC-powered, compact, bench-top unit and PEMM-2 is a battery-powered, belt-mounted unit with embedded controll. Both contain analytical microsystems made from Si-microfabricated components: a dual-adsorbent µpreconcentrator-focuser, a single- or dual-μcolumn separation module, and a μsensor-array detector. The μsensor-array consists of 4-5 chemiresistors (CR) coated with various monolayer-protected Au nanoparticles (MPN), which collectively yield partially selective response patterns that can enhance the recognition/discrimination of VOCs. Other key components include a pre-trap for low-volatility interferences, a split-flow injection valve, and an onboard He carrier-gas canister. In laboratory tests, PEMM-1 demonstrated the determination of 17 VOCs in the presence of 7 background interferences in 8 min. Detection limits were below the corresponding Threshold Limit Values (TLV) of the VOCs. PEMM-2 demonstrated the direct, autonomous determination of 21 VOCs in 6 min, with detection limits ranging from 16−600 ppb, well below TLV levels. A chemometric strategy involving retention time windows was implemented that greatly facilitated vapor recognition and discrimination via the µsensor-array response patterns. Results from a “mock” field test, in which personal exposures to time-varying concentrations of a mixture of five VOCs were measured autonomously, agreed closely with those from a reference GC. Chapter 5 describes the use of a trigonal-tripyramidal room-temperature ionic liquid (RTIL) as a surface modifier for the graphitized carbons, Carbopack B (C-B) and Carbopack X (C-X), used as µpreconcentrator adsorbents. The goal was to impart selectivity for polar compounds, particularly organophosphates and their precursors. Results showed that the capacities for five organophosphorus vapors were consistently enhanced ~2.5-fold with the RTIL-treated adsorbents relative to the untreated adsorbents. Furthermore, the capacities for several non-polar reference vapors were reduced 11 to 26-fold with the modified adsorbents. Implementation in next-generation µpreconcentrator devices is planned.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/151661/1/wjunqi_1.pd