INTERFERENCES DURING MERCURY SPECIATION DETERMINATION BY VOLATILIZATION, CRYOFOCUSING, GAS-CHROMATOGRAPHY AND ATOMIC-ABSORPTION SPECTROSCOPY - COMPARATIVE-STUDY BETWEEN HYDRIDE GENERATION AND ETHYLATION TECHNIQUES

The interfering effects of sodium chloride and a mixture of metal ions on the speciation determination of mercury by derivatization (hydride generation or ethylation), preconcentration by cryotrapping, gas chro matographic separation and detection by quartz furnace atomic absorpti on spectroscopy were investigated, The potential of the masking agent EDTA to overcome the interference was also studied, The experiments we re arranged according to a 2(n) + 1 factorial experimental design, so the possibility of synergistic effects among the variables considered was also taken into account, NaCl interferes in the determination of m ethylmercury (MeHg+) by ethylation, but causes fewer problems in the c ase of inorganic mercury (Hg2+) or if the analysis is carried out by h ydride generation, The presence of metal ions strongly decreases the s ensitivity in the determination of both compounds by hydride generatio n, but has no effect if ethylation is used as the derivatization techn ique. EDTA only partially eliminates the interfering effect of metals in the determination of MeHg+ by hydride generation, It also avoids de composition of MeHg+ to Hg-0, promoted by NaCl, after derivatization o f the compounds by hydride generation, The results obtained are discus sed in terms of a comparison between the two derivatization techniques used, i.e., hydride generation and ethylation, Potential chemical pat hways and reaction mechanisms for the observed interferences are also given.