The combined use of thermal desorption and selected ion flow tube mass spectrometry for the quantification of xylene and toluene in air

Abstract

Thermal desorption (TD) is commonly employed for volatile chemical analysis, it being the method of choice for occupational health and safety monitoring. TD allows for offline capture of volatiles onto a solid sorbent followed by desorption and analysis at a later time. Although TD is routinely used in conjunction with gas chromatography (TD-GC), the assay throughput is low and requires the use of gas standards for quantification. Another technique increasingly employed for volatile chemical analysis, selected ion flow tube mass spectrometry (SIFT-MS), is capable of real-time absolute (i.e. without calibration standards) quantification of volatile chemicals present at single digit parts per billion or higher concentrations. SIFT-MS is, however, normally used for online direct analysis of gas samples rather than offline collection and analysis. The goal of this study was to determine whether a combination of TD and SIFT-MS could be used to quantify volatile compounds, specifically xylene and toluene, more rapidly than TD-GC and without the need for calibration standards. SIFT-MS was able to quantify xylene and toluene levels within 45 s of desorption. Due to the robustness of the SIFT-MS analysis in the presence of water vapour and other major components of air, the purging of tubes usually required to remove these constituents during the TD cycle was not required, therefore reducing the TD cycle time. Comparing the quantity of xylene and toluene applied to the TD tube with the absolute levels quantified by SIFT-MS subsequent to desorption suggested a recovery of over 95% of the applied compound. We conclude that the combination of TD and SIFT-MS allows more rapid and accurate quantification of xylene and toluene (compared with TD-GC) to be achieved without the need for calibration standards, features which may be advantageous in applications requiring rapid analysis and high throughput.

Progress in SIFT‐MS: Breath analysis and other applications

“…This ATD/ SIFT-MS combination not only provides rapid analysis, but the effective preconcentration of trace gases from the sample ultimately lowers their limit of detection to sub-ppb levels. Using standard samples the linearity of this system has been demonstrated within the concentration range from 1 to 10 ppb (Ross & Vermeulen, 2007). Hryniuk and Ross (2009) have now successfully used this ATD/SIFT-MS combination for breath analysis and found that there was a 1 to 1 concordance between the levels of isoprene and acetone in the breath of 12 healthy volunteers as measured using this combination technique and direct real-time SIFT-MS measurements.…”

“…The performance of Profile 3 SIFT-MS instruments has been illustrated by the data presented in several research papers produced by the teams at Keele , 2009Smith et al, 2008;Wang et al, 2008a;Wang, Š paněl, & Smith, 2008b;, at Prague (Španěl, Dryahina, & Smith, 2007a,b,c) and at Thunder Bay (Ross & Vermeulen, 2007;Ross, 2008;Hryniuk & Ross, 2009;Ross, Babay, & Ladouceur, 2009;). Scrutiny of these papers reveals the value and the quality of trace gas analyses obtained using current Profile 3 instruments.…”

“…A more recent development by Ross and Vermeulen (2007) has involved the combination of SIFT-MS with sample collection techniques, specifically automated thermal desorption (ATD) that is more commonly used in combination with GC systems (Phillips & Greenberg, 1991;Jones, Lagesson, & Tagesson, 1995). ATD involves the adsorption of trace gases from air or breath samples onto the surface of a suitable material and their release (by heating) into a neutral gas stream and thence into the detector.…”

Proton Transfer Reaction Mass Spectrometry: Applications in the Life Sciences

“…Experiments using a mixture of Carbograph 2 and Carbograph 5 also showed low breakthrough volumes (<1%) for a number of VOCs, including o-xylene [201]. Ross and Vermeulen [198] observed good correlation between the amount of toluene and xylene applied to tubes containing Carbograph 1TD (one of the adsorbents in our multi-sorbent bed) and the amount measured after thermally desorbing the tubes. Artifact build-up during storage has been reported when using single sorbent tubes.…”

“…However, it is not always possible to bring the source of volatiles and the analytical device together. To circumvent this problem, volatile storage containers can be used such as Teflon or Tedlar bags ( [191]; [192]; [193]), canisters ( [194]; [195]), and Tenax TA or Carbotrap/Carbograph thermodesorption tubes ( [196]; [197]; [198]; [199]). Thermo desorption tubes trap different groups of volatiles depending on the sorbent placed inside the tubes, either by diffusion or by pumping the gas through the tube.…”