Simultaneous Determination of C₁ and C₂-Halocarbons and Monocyclic Aromatic Hydrocarbons in Marine Water Samples at NG/L Concentration Levels

Abstract

A Purge & Trap technique for the analysis of volatile organic compounds (VOCs) combined with GC-MS was applied to measure simultaneously concentrations of 13 C-₁ and C₂-chlorinated hydrocarbons (CHCs) and monocyclic aromatic hydrocarbons (MAHs) down to the I ng/l level. It proved to be impossible to reach this level working with an automated online apparatus because of two reasons. First, the low reproducibility was caused by the water vapour present in the gas stream after purging samples. The second reason was the presence of unpredictable contamination. An off-line purge system, however, combined with thermal dcsorption by means of the on-line apparatus gave reproducible measurements (standard deviations from 2.6 to 15.7%). Contamination was lower than 0.76 ng/l for all VOCs except for benzene, toluene and chloroform. The signal/noise ratio of three corresponded to concentrations below 0.63 ng/l for all VOCs. In this way limits of detection (LODs) of 0.48 (tetrachloroethylene) to 1.25 ng/l (o-xylene) were obtained, except for chloroform benzene and toluene. Their LODs were 4.93, 4.79 and 2.68 ng/l because of the contamination. Precision and accuracy were determined. The long term reliability of the method was evaluated using analytical quality control charts. In addition, sample treatment and storage were checked by adding deuterated surrogates. Results of analysis of water samples taken in the North Sea region and the Scheldt estuary illustrate the applicability of the method. Target compounds were detected in concentrations from 0.5 to 100 ng/l.

Key Words:

• Volatile organic compounds (VOCs)
• C₁- and C,-organochlorines
• monocyclic aromatic hydrocarbons
• purge and trap
• marine pollution