The mass spectrometric characterization of polychlorinated n-alkanes and the methodology for their analysis in the environment

Abstract

The major objective of the research was to develop a method for sensitive and specific analysis of C$\sb{10}$-C$\sb{13}$ polychloroalkanes (PCAs) in environmental samples. Our method of choice became high resolution gas chromatography/electron capture negative ion high resolution mass spectrometry (HRGC/ECNI-HRMS) in the selected ion monitoring (SIM) mode. The development of the method involved several steps: (a) Because commercial PCA preparations may contain several thousands of compounds, eight representative compounds of known structure were synthesized in order to examine their chromatographic and mass spectral properties. (b) The electron ionization (EI) positive ion mass spectra, generated with a Kratos Concept (EBE geometry) mass spectrometer, were interpreted with the aid of unimolecular and collision assisted dissociation mass spectra, and enthalpy of formation and force-field estimates of strain energy of ions. (c) ECNI mass spectra were investigated under various ion source conditions to find optimum parameters for sensitivity. (d) Based on these results, a profile of the components of significant abundance in the PCA is determined by an ECNI selected ion monitoring method. (e) Finally, a quantitative analytical procedure was developed. Total PCA concentrations ($\Sigma$PCAs) in sediment samples from the mouth of the Detroit River (MI) (0.3 $\mu$g/g) were higher than of $\Sigma$DDT $\Sigma$DT plus metabolites) (0.19 $\mu$g/g) but lower than of $\Sigma$PCBs (1.5 $\mu$g/g) and $\Sigma$PCTs (2.5 $\mu$g/g). $\Sigma$PCA levels in yellow perch (1.0 $\mu$g/g) were similar to $\Sigma$PCB levels in silver bass (0.09-1.2$\mu$g/g). Mean $\Sigma$PCA levels $(n=5)$ in air samples from Egbert, Ont., (44$\sp\circ$ 14$\sp\prime$ N, 79$\sp\circ$ 47$\sp\prime$ W), collected in 1990, were 543 $\pm$ 318 pg/m$\sp3$, which is similar to $\Sigma$PCB levels (74-682 pg/m$ sp3$) reported earlier. The highest observed $\Sigma$PCA concentration of 924 pg/m$\sp3$ was higher than the highest $\Sigma$PCB concentration ($\Sigma$ = 91 congeners), $\sim$682 pg/m$\sp3.$ The mean $\Sigma$PCA concentration for water collected over a six month period from Selkirk, MB, of 30 $\pm$ 14 ng/L was significantly higher than that of $\Sigma$PCBs (1.1 $\pm$ 1.2 ng/L). Concentrations of $\Sigma$PCAs in beluga whales (Delphinapterus leucas) from the St. Lawrence River estuary were higher than in blubber samples from a variety of marine mammals from various regions of the Arctic. Sediment cores from 4 Canadian lakes ranging from 49$\sp\circ$N to 81$\sp\circ$N, were also analyzed for PCAs. Concentrations of total PCAs in surface sediments from Lake Winnipeg (50$\sp\circ$N/96$\sp\circ$W, Manitoba) and Hazen lake (81$\sp\circ$N/71$\sp\circ$W, High Arctic) were 176 and 4.5 ng/g (dry wt), respectively, corresponding surficial fluxes were 147 and 0.9 $\mu$g/m$\sp2$ yr. The high flux of PCAs to Lake Winnipeg suggests local contamination. The surficial flux of PCAs to Fox lake (61$\sp\circ$N/135$\sp\circ$W), a sub-arctic lake in the Yukon, was also high, 34 $\mu$g/m$\sp2$ yr, but much lower in Lake Nipigon (49$\sp\circ$N/89$\sp\circ$W, N.Ontario), 3 $\mu$g/m$\sp2$yr. (Abstract shortened by UMI.)