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Cold vapor atomic absorption spectrometry (CV-AAS) based on photochemical reduction by exposure to UV radiation is described for the determination of methylmercury and total mercury in biological samples. Two approaches were investigated: (a) tissues were digested in either formic acid or tetramethylammonium hydroxide (TMAH), and total mercury was determined following reduction of both species by exposure of the solution to UV irradiation; (b) tissues were solubilized in TMAH, diluted to a final concentration of 0.125% m/v TMAH by addition of 10% v/v acetic acid and CH(3)Hg(+) was selectively quantitated, or the initial digests were diluted to 0.125% m/v TMAH by addition of deionized water, adjusted to pH 0.3 by addition of HCl and CH(3)Hg(+) was selectively quantitated. For each case, the optimum conditions for photochemical vapor generation (photo-CVG) were investigated. The photochemical reduction efficiency was estimated to be approximately 95% by comparing the response with traditional SnCl(2) chemical reduction. The method was validated by analysis of several biological Certified Reference Materials, DORM-1, DORM-2, DOLT-2 and DOLT-3, using calibration against aqueous solutions of Hg(2+); results showed good agreement with the certified values for total and methylmercury in all cases. Limits of detection of 6 ng/g for total mercury using formic acid, 8 ng/g for total mercury and 10 ng/g for methylmercury using TMAH were obtained. The proposed methodology is sensitive, simple and inexpensive, and promotes "green" chemistry. The potential for application to other sample types and analytes is evident.

Ruthenium, deposited on a L'vov platform, is proposed as a permanent modi®er for the determination of Ag, Pb and Sn in aqua regia extracts from sediments by electrothermal atomic absorption spectrometry. The coating process is simple: a solution containing Ru is pipetted repeatedly on to the platform inserted in a graphite tube and is submitted to a temperature program. In a 50% v/v aqua regia solution, high pyrolysis temperatures could be used: 1200 ³C for Ag and Pb, and 1500 ³C for Sn. At these temperatures, similar characteristic masses to those found for a nitric acid medium, using a Pd±Mg modi®er, were obtained, showing that the high concentration of chloride does not interfere with the determination. In the aqua regia medium, the permanent modi®er is much superior in comparison with Pd or PdzMg, modi®ers applied as a solution, which could not stabilize the analytes satisfactorily. Very long tube lifetimes, around 1700 cycles, were obtained for Pb and Sn in this medium. Three sediment reference materials were partially dissolved using a mixture of aqua regia and hydrogen peroxide in a microwave oven. The results for Ag and Pb were in agreement with the recommended values, demonstrating the ef®ciency of the extraction. However, for Sn, the precison was less satisfactory, indicating that the extraction may be less ef®cient and reproducible for this analyte. Other advantages of the permanent Ru modi®er are the low blanks due to in situ cleaning of the modi®er and the shorter analysis time in comparison with the modi®ers in solution.

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