Limitations of low resolution mass spectrometry in the electron capture negative ionization mode for the analysis of short- and medium-chain chlorinated paraffins
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The analysis of complex mixtures of chlorinated paraffins (CPs) with short (SCCPs, C10–C13) and medium (MCCPs, C14–C17) chain lengths can be disturbed by mass overlap, if low resolution mass spectrometry (LRMS) in the electron capture negative ionization mode is employed. This is caused by CP congeners with the same nominal mass, but with five carbon atoms more and two chlorine atoms less; for example C11H17 37Cl35Cl6 (m/z 395.9) and C16H29 35Cl5 (m/z 396.1). This can lead to an overestimation of congener group quantity and/or of total CP concentration. The magnitude of this interference was studied by evaluating the change after mixing a SCCP standard and a MCCP standard 1+1 (S+MCCP mixture) and comparing it to the single standards. A quantification of the less abundant C16 and C17 congeners present in the MCCP standard was not possible due to interference from the major C11 and C12 congeners in the SCCPs. Also, signals for SCCPs (C10–C12) with nine and ten chlorine atoms were mimicked by MCCPs (C15–C17) with seven and eight chlorine atoms (for instance C10H12Cl10 by C15H24Cl8). A similar observation was made for signals from C15–C17 CPs with four and five chlorine atoms resulting from SCCPs (C10–C12) with six and seven chlorine atoms (such as C15H28Cl4 by C10H16Cl6) in the S+MCCP mixture. It could be shown that the quantification of the most abundant congeners (C11–C14) is not affected by any interference. The determination of C10 and C15 congeners is partly disturbed, but this can be detected by investigating isotope ratios, retention time ranges and the shapes of the CP signals. Also, lower chlorinated compounds forming [M+Cl]− as the most abundant ion instead of [M-Cl]− are especially sensitive to systematic errors caused by superposition of ions of different composition and the same nominal mass.
KeywordsPolychlorinated n-alkanes Chlorinated paraffins ECNI low resolution mass spectrometry Self-interferences
The financial support from the German Federal Environmental Agency and the Swiss National Science Foundation under Project 2000.064817.01 and 200020–101473.01 is greatly appreciated.
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