Determination of the Sum of Short Chain Polychlorinated n‐Alkanes with a Chlorine Content of Between 49 and 67% in Water by GC‐ECNI‐MS and Quantification by Multiple Linear Regression

Abstract

AbstractThis new approach for the quantification of the sum of short chain polychlorinated alkanes in mixtures (commonly abbreviated as SCCPs, where P stands for paraffin) with average chlorine contents between 49 and 67% and different C‐number distributions is the background for ISO CD 12010, allowing standardized analysis according to the European water framework directive in unfiltered surface water, ground water, drinking water and waste water. A quantification method for the sum of short chain polychlorinated n‐alkanes by GC‐ECNI‐MS (gas chromatography coupled with electron capture chemical ionization mass spectrometry), independent of the chlorine content and robust against changes in C‐number distribution, was developed. This means that the very different response factors in GC‐ECNI‐MS, depending on the chlorine content, are no longer a problem for the analysis of SCCPs. Furthermore, problems with the selection of analytical standards due to batch dependent technical mixtures and different environmentally occurring mixtures can be overcome by using this robust method. The calibration was performed using synthetic mixtures mimicking a variety of different technically produced SCCP mixtures with average chlorine contents between 49 and 67% and different C‐number distributions. By this means, the calibration is also traceable. The method was based on the integration of selected m/z value (mass/charge relation value) signals over the full retention range of the compounds. Quantification was performed using multiple linear regression calibration with two selected m/z signals, and verified with two other mass combinations. The selection of the m/z values used for quantification was carried out by means of an orthogonal calibration design. A stepwise procedure was utilized to produce the best quantification results, with the minimum number of quantification m/z signals, together with the minimization of potential interferences to be encountered in water analysis. The weighted sum of the peak areas of two m/z values, m/z 327 and 423, led to a sum determination which was applicable to the different SCCP mixtures most likely to be found in the aquatic environment. The problem with the very different response factors of the selected m/z values in GC‐ECNI‐MS, caused by the differing chlorine content of the SCCP mixtures, was overcome as well by forming the weighted sum of the two selected peak areas. The method was especially suitable for water analysis because of the low detection limit achieved by GC‐ECNI‐MS for chlorinated compounds.