Deconvolution of Mass Spectral Interferences of Chlorinated Alkanes and Their Thermal Degradation Products: Chlorinated Alkenes

Abstract

Chlorinated paraffins (CPs) are high production volume chemicals and ubiquitous environmental contaminants. CPs are produced and used as complex mixtures of polychlorinated n-alkanes containing thousands of isomers, leading to demanding analytical challenges. Due to their high degree of chlorination, CPs have highly complex isotopic mass patterns that often overlap, even when applying high resolution mass spectrometry. This is further complicated in the presence of degradation products such as chlorinated alkenes (CP-enes). CP-enes are formed by dehydrochlorination of CPs and are expected thermal degradation products in some applications of CPs, for example, as metal working fluids. A mathematical method is presented that allows deconvolution of the strongly interfered measured isotope clusters into linear combinations of isotope clusters of CPs and CP-enes. The analytical method applied was direct liquid injection into an atmospheric pressure chemical ionization source, followed by quadrupole time-of-flight mass spectrometry (APCI-qTOF-MS), operated in full scan negative ion mode. The mathematical deconvolution method was successfully applied to a thermally aged polychlorinated tridecane formulation (Cl-Cl). Deconvolution of mass patterns allowed quantifying fractions of interfering CPs and CP-enes. After exposure to 220 °C for 2, 4, 8, and 24 h, fractions of CP-enes within the respective interfering clusters increased from 0-3% at 0 h up to 37-44% after 24 h. It was shown that thermolysis of CPs follows first-order kinetics. The presented deconvolution method allows CP degradation studies with mass resolution lower than 20000 and is therefore a good alternative when higher resolution is not available.

Carbon Chain Decomposition of Short Chain Chlorinated Paraffins Mediated by Pumpkin and Soybean Seedlings

“…Compared with the chlorine atoms of parent SCCPs, the dechlorination and chlorine rearrangement products were all identified by ECNI. 43 The selected parent SCCPs contained 10, 11, and 13 carbon atoms, respectively. However, the daughter chemicals included SCCPs containing 12 carbon atoms.…”

Developments and interlaboratory study of the analysis of short-chain chlorinated paraffins

“…2,3,4,5,6,7heptachloroundedecane) remains unachieved by single-column GC or liquid chromatography (LC), resulting in a typical wide lump in the chromatogram and strong interference with other CPs such as medium-chain chlorinated paraffins (MCCPs) and compounds with similar retention times. Separation between congener groups, other fragmenting ions, and other compounds by mass spectrometry (MS) is difficult too, as at least a mass resolution of 20,000 (full width at half height) is needed [6]. For Cl 5 with electron-capture negative ionization MS (ECNI-MS) have a mass to charge ratio (m/z) of 395.9 and 396.1, respectively.…”

Environmental Risks of Medium-Chain Chlorinated Paraffins (MCCPs): A Review

“…However, mass spectrometers with a resolution below 10 000 FWHM are not able to resolve the commonly occurring mass interferences from different CP congener groups (for example interferences between 12 ) An increased response factor of the longer-chained CPs will increase this percentage even further. 74 In addition to the commonly occurring mass interferences, other mass interferences from, for example, transformation products 79 or unexpected fragment ions formed during the ionization can complicate the analysis even more. However, Schinkel et al 79,81 and Yuan et al 80 showed that it is possible to identify the target congeners when applying deconvolution procedures.…”