Usefulness of the chemical modification and the multi-injection technique approaches in the electrothermal atomic absorption spectrometric determination of silver, arsenic, cadmium, chromium, mercury, nickel and lead in sea-water

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Abstract
A critical study of the use of chemical modification and background correction systems was carried out for the direct determination of several high and medium volatility and refractory metals (Ag, As, Cd, Cr, Hg, Ni and Pb) in sea-water samples by ETAAS. The influence of increasing sea-water inorganic matrix on the atomic signals, by the introduction of a large injection volume, was evaluated for different chemical modifiers [mainly Pd(NO3)2 , Mg(NO3)2 and also reduced palladium, which was done by using different reducing agents, viz., ascorbic acid, hydroxylamine hydrochloride and citric acid] and with two background correction systems [deuterium arc background correction (DABC) and Zeeman effect background correction (ZEBC)]. The influence of the salt matrix from sea-water was found to be very important for medium volatility metals such as Ag, As and Pb (charring temperatures between 1100 and 1400 °C), whereas for refractory (Cr and Ni, with charring temperatures of 1500 and 1600 °C, respectively) and high volatility metals such as Cd and Hg (charring temperature of 500 and 300 °C, respectively) this influence was insignificant. By using chemical modification and background correction, the interferences from the saline matrix were lowered for all metals studied (except Pb) and their direct determination in sea-water samples became possible. For high and medium volatility metals the use of reduced palladium offers better analytical performance than the use of palladium nitrate, while the addition of reducing agents does not improve the analytical performance for refractory metals.

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