Data quality improvement for field-portable gas chromatography-mass spectrometry through the use of isotopic analogues for in-situ calibration

Abstract

Environmental contextQuantitative field-based sampling of airborne volatile organics continues to be a challenge because of the absence of laboratory supplies and facilities. Approaches are required to overcome poor data arising from difficulties with calibration of fielded instruments. This method normalises responses across portable thermal desorption gas-chromatography mass spectrometers and requires no advance calibration, enabling accurate and precise use of previously established response factors ported from the laboratory to fielded instruments. AbstractSorbent capture provides a process for collecting airborne volatile organic compounds (VOCs) for analysis by thermal desorption gas chromatography-mass spectrometry (TD-GC-MS). Under typical laboratory conditions, analytical standards are readily available and calibration of instrumentation is a routine process. In contrast, field-portable instruments are standardised using a representative curve prepared on a limited number of instruments and then applied to fielded units. The performance of field-portable TD-GC-MS systems when deployed to multiple remote sites was studied, and a large variability in sensitivity and performance was observed when using the manufacturer-prescribed methods for calibration of instruments and normalisation of the data. This variability was remedied by the implementation of a non-interfering calibration that is pre-incorporated onto the sorbent media. Use of an in-situ calibration curve constructed using stable isotope labelled standards provided robust quantification, accuracy of measurement and diagnostic capabilities for malfunctioning fielded equipment. Pre-incorporation of isotopic analogues onto thermal desorption tubes in advance of field distribution greatly improves the accuracy and reproducibility of analyses and demonstrates, for the first time, definitive quantification of target analytes using field-portable GC-MS in an operational theatre.