Determination of Ag, Pb and Sn in aqua regia extracts from sediments by electrothermal atomic absorption spectrometry using Ru as a permanent modifier

Ruthenium, deposited on a L'vov platform, is proposed as a permanent modifier 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 degrees C for Ag and Pb, and 1500 degrees C for Sn. At these temperatures, similar characteristic masses to those found for a nitric acid medium, using a Pd-Mg modifier, were obtained, showing that the high concentration of chloride does not interfere with the determination. In the aqua regia medium, the permanent modifier is much superior in comparison with Pd or Pd + Mg, modifiers 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 efficiency of the extraction. However, for Sn, the precison was less satisfactory, indicating that the extraction may be less efficient and reproducible for this analyte. Other advantages of the permanent Ru modifier are the low blanks due to in situ cleaning of the modifier and the shorter analysis time in comparison with the modifiers in solution.