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Calibration and performance of synchronous SIM/scan mode for simultaneous targeted and discovery (non-targeted) analysis of exhaled breath samples from firefighters
Wallace, A., J. Pleil, S. Mentese, K. Oliver, D. Whitaker, AND K. Fent. Calibration and performance of synchronous SIM/scan mode for simultaneous targeted and discovery (non-targeted) analysis of exhaled breath samples from firefighters. JOURNAL OF CHROMATOGRAPHY A. Elsevier Science Ltd, New York, NY, 1516:114-124, (2017).
Many environmental and health studies begin with broad investigations of potentially harmful sources, which are followed by more specific methods that focus only on constituents of interest. For example, target screening revealed that of the thousands of compounds in liquid JP-8 jet fuel, four n-alkanes (C9 to C12) constituted the fingerprint of the fuel and that a series of single-ring aromatic compounds (benzene, toluene, naphthalene, etc.) could be used as markers of adverse health outcomes. Subsequently, only a handful of target compounds were analyzed from the breath of Air Force base personnel to efficiently assess exposures (Pleil et al. 2000). The inverse of this approach has also been implemented. For example, if certain halogenated compounds from water disinfection are suspected to be harmful, then only those compounds are targeted in exhaled breath to document potential exposures (Pleil and Lindstrom 1997). However, what if there are unanticipated sources of contamination in the water, such as methyl tertiary butyl ether (MTBE) or trichloroethylene and vinyl chloride from surface infiltration from spills (e.g., Lindstrom and Pleil 1996a, 1996b)? What if an unknown infectious state of the human subject introduced bacterial off-gas products into the sample (Pleil et al. 2015, Leja et al. 2016)? In these cases, the targeted methods would fail to detect these compounds and products, which could interfere with sample integrity or lead to a false assessment of health state. Therefore, a combination of targeted and non-targeted work could be important both for protecting health and in other applications of clinical practice, such as pulmonary testing and hypoxia, forensic science, and national security (Brodrick et al. 2015, Harshman et al. 2015, Pleil et al. 2016). This has traditionally required separate instrumental methods as described below, and depending upon sampling schemes, could even require 205 additional sample collections.
Traditionally, gas chromatography – mass spectrometry (GC-MS) analysis has used a targeted approach called selected ion monitoring (SIM) to quantify specific compounds that may have adverse health effects. Due to method limitations and the constraints of preparing duplicate samples, the information that could be obtained from separately collecting the full scan chromatogram of the sample has often been sacrificed. However, a hybrid technique called synchronous SIM/scan mode that switches back and forth between the two acquisition methods has become available from equipment manufacturers that maintains the accuracy and sensitivity of SIM for targeted analysis while also providing the full scan chromatogram for discovery of non-target compounds. We have explored the value and performance of this new technology using calibration data and real-world breath samples from a joint EPA/NIOSH collaboration that assessed the safety of firefighters’ protective gear during controlled structural burns. Collecting field samples is costly and must be performed strategically to ensure that time points and replicates are accurate and representative of the intended population. This is especially difficult, if not impossible, to accomplish with firefighters who are working under volatile conditions. The synchronous SIM/scan method decreases the number of field samples that need to be collected by half and reduces error in trying to recreate time points since a breath sample from a single sorbent tube can be used to collect both the SIM and scan data simultaneously. This work demonstrates the performance of the technology using calibration data. As a practical demonstration of the method, we investigate thirty-six firefighter breath samples, document organic compounds of interest, and identify additional non-target compounds.
Record Details:Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL EXPOSURE RESEARCH LABORATORY
EXPOSURE METHODS & MEASUREMENT DIVISION