engleski

Microwave-assisted extraction of polychlorinated biphenyls from pine needles

Polychlorinated biphenyls (PCBs) are persistent, lipophilic, bio-accumulative and toxic compounds. In spite of bans and restrictions of PCB use all over the world, they are still present in all parts of the biotic and abiotic environment. Pine needles have often been used as a bioindicator for environmental levels of organochlorine compounds (1, 2, 3). The surface of pine needles acts as a passive sampler for lipophilic compounds such as PCBs from the surrounding air. The difficulties encountered in the analysis of PCBs in pine needles include the complexity of wax composition, many anthropogenic interferences and low concentrations of analytes. Various extraction methods have been performed for the extraction of organochlorine compounds from pine needles: shaking with appropriate organic solvent (1), Soxhlet extraction (2), ultrasonic extraction (3) and recently, accelerated solvent extraction (4). Until now, microwave-assisted extraction (MAE) has been used for environmental matrices such as soil, but not for pine needles. The aim of this study was to investigate application of MAE in the extraction of six indicator PCBs (PCB-28, PCB-52, PCB-101, PCB-138, PCB-153, PCB-180 ; numbered according to IUPAC) from pine needles. PCBs were extracted from dried and ground needles (5 g) using dichloromethane (20 mL). Extractions were carried out in Teflon PFA extraction vessel (GreenChem Plus) using Microwave Accelerated Reaction System for Extraction MarsX (CEM, USA). MAE conditions are shown in Table 1. Due to the complex composition of wax, multistage cleanup was required. The analysis was done on a gas chromatograph with a 63Ni electron capture detector. Details about cleanup procedure and gas chromatographic conditions have been described earlier (5). This study investigated the effects of power, extraction temperature and time on PCB analysis. At 600 W and 1200 W, five and two combinations of temperature and time were applied, respectively. Recovery and repeatability of the method were tested by adding 4 ng of analyzed PCB congeners per gram of dried ground pine needles and left standing 24 hours. The recoveries of PCBs were calculated after subtracting the mean levels of two non-fortified samples from the fortified ones. Although analytes recoveries (6 % to 70 %) overlapped in all applied MAE conditions, the repeatability of the method, expressed as RSD, depend on MAE conditions. When extraction temperature was 80 °C or 110 °C at 600 W and 1200 W, the repeatability was not satisfactory. The treatment time was between five and 40 minutes and the results indicate that repeatability was not affected by time. At 40 °C, repeatability was improved and RSDs were below 35 %. Unsatisfactory repeatability was probably caused by to high temperature, and the resulting interferences were not time-dependent. In conclusion, the recoveries were not high probably due to the multiphase clean-up, which was absolutely necessary, due to low PCB levels in pine needles and also due to incomplete extraction. At 1200 W, 40 °C and 15 minutes extraction time, for all compounds reproducibility was below 35% and it was concluded that in spite of relatively low recoveries (31 % to 44 %), the method is suitable for PCB analyses from pine needles. Similar low recoveries were also obtained with extraction method used earlier (5). An advantage of MAE over other conventional extraction techniques is that it takes small quantities of solvent and short extraction time. References: [1] S. Jensen, G. Eriksson, H. Kylin, Chemosphere 24 (1992) 29-245. [2] W.A. Ockenden, E. Steinnes, C. Parker, K.C. Jones, Environ. Sci. Technol. 32 (1998) 2721-2726. [3] K.-D. Wenzel, L. Weißflog, E. Paladini, M. Gantuz, P. Guerreiro, C. Puliafito, G. Schüürmann, Chemosphere 34 (1997) 2505-2518. [4] K-D. Wenzel, A. Hubert, M. Manz, L. Weissflog, W. Engelwald, G. Schüürmann, Anal. Chem. 70 (1998) 4827-4835. [5] S. Herceg Romanić and B. Krauthacker, Bull Environ Contam Toxicol 72 (2004) 1203-1210.

indicator PCBs; organochlorine compounds; microwave-assisted extraction; pine needles

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