Measurement artefacts, ion mobility and other observations in environmental mass spectrometry analyses

Many laboratories are engaged in the measurement of persistent organic pollutants, particularly polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzo-furans (PCDFs) and polychlorinated biphenyls (PCBs), to satisfy various investigative needs and compliance requirements worldwide. However, from a mass spectrometry perspective, the current mandated methods have changed little since their origins in the 1980s and 1990s and fail to address certain issues that can lead to the erroneous rejection or filtering of data, and conversely, to the acceptance of data that may be considered questionable. Notwithstanding any legislative requirements, since the goal of these analyses is ultimately related to human or animal health, producing accurate and reliable data is of the utmost importance. This research highlights various areas of concern and aims to improve upon the current peak identification and measurement practices that can lead to such false negatives, false positives and other errors. A key contribution made by this thesis concerns the role of ion statistics in peak area measurement and its subsequent effect on isotope ratio determination – a primary parameter (together with chromatographic retention time) for compound identification in both high-resolution mass spectrometry (HRMS) and tandem mass spectrometry (MS/MS) methods. In an allied area of research, a comprehensive study of all mono- to deca-chlorinated biphenyls using atmospheric pressure chemical ionisation, both for fragmentation analysis and in conjunction with ion mobility spectrometry (IMS), was undertaken. An additional original contribution described in this thesis shows that, in addition to certain structural information – especially in relation to the degree of chlorine ortho substitution – there are some unusual shifts in the measured IMS arrival time distributions of certain PCB isotopologues and isotopomers suggesting the occurrence of isomerisation in the gas phase. Other patterns emerging from these data are indicative of the toxicity of certain PCBs, both correlating with known toxic congeners and others that are currently classified as non-toxic.