A new method for the routine trace analysis of polychlorinated biphenyls in waste oil and contaminated soil

Abstract

Polychlorinated biphenyls (PCBs) were used in various industries and equipment such as transformers, paints and capacitors until 1979. PCBs enter the environment through improper disposal by users and manufacturers. The Stockholm Convention on persistent organic pollutants of which South Africa is a signatory states the identification and removal of PCB containing equipment with levels higher than 50 mg/l. PCB analysis in oils and oil contaminated soil is normally expensive in terms of time, instrumentation and uses large volumes of hazardous solvents which further increase cost per sample. Commercial laboratories are constantly under pressure to provide a faster turnaround time per sample at low cost and of an acceptable quality, therefore, a new method was developed to find a balance between these requirements. Numerous methods exist for the extraction and analysis of PCBs in waste oils and soils such as liquid-liquid extraction (LLE) and solid phase extraction (SPE) coupled with detection on GC-MS (gas chromatography- mass spectrometry). Most methods for the extraction and analysis of PCBs are laborious, time consuming and are of high cost per sample which is not suited for a commercial environment where sample throughput is also of cardinal importance. The newly developed method utilizes the interaction of PCBs with dimethylsulphoxide (DMSO) for a fast liquid-liquid extraction that was combined with solid phase microextraction (SPME). For implementation in a commercial laboratory limited sample clean-up is a necessity and, therefore, the sensitivity and selectivity of GC-MS/MS (gas chromatography mass spectrometry/ mass spectrometry) was used. GC-MS/MS is able to filter out most spectral interferences and provides a high level of confidence in terms of identifiers. This fast liquid-liquid extraction using small amount of solvent and automated submerged SPME GCMS/ MS makes this method ideal for commercial laboratories, low cost per sample, fast turnaround time and provides a quality result. Cost is further reduced by using GC-ECD (electron capture detector) for screening of samples, GC-ECD is extremely sensitive for halogenated compounds, ideal for PCB analysis. Robustness of any method is important and more so for commercial laboratories. PCBs were successfully extracted from soil and various oils. Current regulatory limits for total PCBs are 50 mg/l in oil and 610 μg/kg in soil. This method offers a quantification limit of 5.35 mg/l in waste oil and 35 μg/kg in soil which is below the allowed maximum contamination levels (MCL) of these matrices.