Analysis of arsenic species in fish after derivatization by GC-MS

The derivatization of organoarsenic compounds by different reagents like thioglycolates or dithiols and the subsequent analysis by GC-MS as a molecular specific technique was investigated and described. The possible derivatization reagents methyl- and ethylthioglycolate (TGM and TGE), 1,3-propane- and 1,5-pentanedithiol (PDT and PeDT), which transfer the polar and nonvolatile analytes dimethylarsenate (DMA), monomethylarsonate (MMA), arsenite and arsenate into volatile compounds, were evaluated. The application for real samples like fish material was also studied. In addition the gas chromatographic separation and resolution was optimized and experiments were carried out to determine the highest derivatization rates. Derivatization reagents were evaluated in terms of quantity and stability of the formed chemical species. All derivatization products were characterized by mass spectrometry in order to identify the separated arsenic species. The most efficient conversion of DMA and MMA was observed by using ethylthioglycolate as derivatization agent. Finally, the derivatization procedure and the GC-MS-method were validated to determine linearity, precision, selectivity, analytical limiting values and recoveries. For the proposed method a limit of detection (LOD) of 5.8 pg for DMA and 14.0 pg for MMA was found. The accuracy was established by comparing the mean value measured for DMA in the certified reference material BCR-627 (tuna fish) with the certified one. MMA was not quantified in marine samples due to its low content. In shrimp samples DMA was not detectable. For codfish a DMA-content of 0.20±0.004 mg kg(-1), for "Surströmming" an amount of 0.38±0.02 mg kg(-1) and for herring, which showed the highest amount of DMA, a content of 1.15±0.03 mg kg(-1) was determined.