engleski

Intralaboratory testing of method for the determination of organochlorine compounds in pine needles

Pine needles are covered with epicuticular wax (long-chain esters, polyesters and paraffin mainly) which has ability to absorb airborne lipophilic pollutants. This fact makes pine needles suitable for biomonitoring at a selected site. Polychlorinated biphenyls (PCB) and organochlorine pesticides are two groups of synthetic, lipophilic, aromatic compounds intensely used over the last decades. These compounds are present in pine needles at ppb levels and differences in samples from site to site are very small. Therefore, a reliable accurate and precise method is necessary for monitoring studies. The aim of this work was to introduce a method for determination of six PCB congeners (PCB-28, PCB-52, PCB-101, PCB-138, PCB-153, PCB-180 IUPAC numbering system) and organochlorine pesticides (HCB, a-HCH, b-HCH, g-HCH, p,p˘-DDT and its metabolites p,p˘-DDD and p,p˘-DDE) in pine needles. The method of Franich and co-workers (Frasenius J. Anal. Chem. 1993; 337:347) was adopted and modified. To dried grounded needles dichloromethane was added and the organochlorine compounds were extracted. Due to the complexity of wax composition multistage clean up was required. Waxes were repeatedly precipitated by cooling. Clean up of extracts was continued by saponification under alkaline conditions and adsorption chromatography on multilayer silica column (containing silica gel impregnated with sulphuric acid and silica gel with sodium hydroxide). Purified extracts were evaporated and polychlorinated biphenyls and organochlorine pesticides determined by HRGC/ECD on two different capillary columns. Recovery and repeatability have been determined by the addition of known amounts of compounds to subsamples of dried ground needles extracts at three levels: 0,2-0,8 ng/g, 0,9-2,8 ng/g and 6,9-27,0 ng/g of dried sample. For each fortification level, five subsamples were analysed. At the first level the recoveries were poor because the amount of compounds added was near the determination limit. Recoveries ranged between 32% and 94% (depending on the compound) at the second level, and between 25% and 59% at the third level. Relative standard deviations (RSD in %) for repeatability were below 52%, with the exception of g-HCH (61%), PCB-28 (73%) and PCB-52 (78%) at the second level. At the third level RSD were below 55% with the exception of g-HCH (65%) and p,p˘-DDE (61%). Within-laboratory reproducibility has been tested over a longer period on samples collected at different sites by addition of 0,9-2,8 ng compound per gram of dried sample. Recoveries ranged between 29% and 54% while RSD ranged between 23% and 55% depending on the compound. Although the recoveries were not very high they were repeatable and, considering the levels of compounds present in the pine needles, it is considered that the method is suitable for monitoring studies.

organochlorine pesticides; polychlorinated biphenyls; extraction from pine needles; gas chromatographic analysis

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