Wake up and smell the...VOC
Volatile organic compounds (VOCs) are organic chemicals that have a high vapour pressure at room temperature. This is due to their low boiling point which means they typically vaporize easily (transition from liquid or solid to a gas) - and this can make them somewhat tricky to analyse. However, below, we offer some solutions on experimental set-ups to make your VOC analysis easier...
Most smells, scents or odours are the result of one or more VOCs detected by the human nose and VOCs are all around us – from perfumes to paints and cosmetics to cleansers. As a result, they are the subject of much experimental research with applications in food and flavour science, biological research, medicine and the environment. For example in flavour science, back in 2008, scientists at the Nestle Research Center (Lausanne, Switzerland), reported a system that predicted the sensory profile of coffee using mass spectrometry to ionize and analyse the hot gases wafting above the coffee surface, (1).
This can be taken one step further – the development of a flavour ingested by a person can be examined in their exhaled breath. This data can be used for food design, e.g. for adjusting the intensity and duration of a food flavour tested by the consumer. The exhaled human breath contains a few thousand VOCs and can be used not only for food and flavour science but also as a “breath biopsy” - to serve as a VOC biomarker to test for diseases such as lung cancer (2). One study has shown that VOCs are “mainly blood borne and therefore enable monitoring of different processes in the body” (3). Exhaled VOCs are being studied for their potential to diagnose a variety of different medical conditions from Alzheimers to diabetes.
This is an area that Cellix explored in depth in the European funded "SniffPhone" project, co-ordinated by Prof. Hossam Haick from Technion University. Cellix worked with partners to develop a tool for the collection and analysis of VOCs from exhaled breath specific for gastric cancer. The volatile markers suggested for study included 2-Propenenitrile, Isoprene, 6-Methyl-5-hepten-2-one, Alpha-methyl-styrene, 1,2,3-Trimethylbenzene, Furfural and 2 Butanone. This involved determining typical gastric cancer VOC profiles collected in exhaled breath while taking into account the diluting indoor/outdoor environment. We examined different exhalation situations / kinetics using real-time mass spectrometry methods with the long-term goal of creating viable protocols for patient single-time screening and continuous screening. The success of this project resulted in SniffPhone winning the Innovation Award from the European Commission. Check out the SniffPhone video below which highlights some of our work in this area:
VOC Experimental Set-up
In our experimental set-up, we used our 4U pressure pump with 3 channels dedicated to VOC samples (#1: Acetone; #2: Ethanol and #3: Isopropanol) which were pre-dissolved in water at known concentrations before passing through our flow sensors, as shown in the schematic below. The samples were vaporized at 140 degC and then pumped, via a heated transfer line at 45 degC, to a mass spectrometer. Ions are separated in the mass analyser according to their mass to charge ratio (m/z), and transferred to the detector for identification.
Mass Spectrometry Results
The spectral scans of each of the 3 VOC channels (#1: Acetone; #2: Ethanol and #3: Isopropanol) were acquired over a time period of 12 hours as shown in the screenshot below. The mass spectrometry results confirmed that the VOCs were correctly generated. This experimental set-up enables many VOCs to be pre-dissolved in water at a known concentration and subsequently pumped into a mass spectrometer or gas sensor giving the user many possibilities of VOC analysis.
Christian Lindinger et al. When Machine Tastes Coffee: Instrumental Approach to Predict the Sensory Profile of Espresso Coffee. Anal. Chem. 2008, 80, 5, 1574-1581. Published 26 January 2008. doi: 10.1021/ac702196z
B. A. Buszewski et al. Human exhaled air analytics: Biomarkers of diseases. Biomedical Chromatogrphy. 21 (6): 553-566. (2007) doi: 10.1002/bmc.835
Wolfram Miekisch et al. Diagnostic potential of breath analysis – focus on volatile organic compounds. Clinica Chimica Acta. 347 (1-2): 25-39. (2004) doi: 10.1016/j.cccn.2004.04.023