Ultrasonic solid-liquid extraction (USLE) of trace metals from biological and environmental samples and its subsequent quantification by electrothermal atomic absorption spectrometry (ET-AAS) is nowadays an emerging methodology in the analytical laboratory. However, this methodology is far from maturity as can be readily demonstrated from the controversial data reported by different workers. In the light of our own experience and a survey of published data, a general approach for USLE-ET-AAS is discussed, taking into account the different variables which affect ultrasonic solid-liquid extraction, namely, the ultrasonic device chosen for ultrasonic extraction (e.g. ultrasonic bath or ultrasonic probe), particle size, acid concentration, sonication time and sonication amplitude, sample mass and analyte-matrix binding.

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Different oxidation methodologies based on ozone and focused ultrasound for the degradation of organic matter and organic-mercury compounds (spiked) present in human urine are discussed. Inorganic and total mercury can be determined in human urine. A flow-injection cold-vapour atomic absorption spectrometer system was used for mercury measurements. Optimization of cold vapour generation was performed with NaBH4 and SnCl2. A two-level full factorial design (2(4)) was applied to understand the cross-effects among the variables influencing the degradation of organic-mercurials and organic matter in urine by KMnO4/HCl/focused ultrasound, namely, KMnO4 and HCl concentration, ultrasonication time and ultrasonication amplitude. Optimization results showed that all variables were significant. New trends in the application of focused ultrasound and ozone are highlighted. As a result of the optimization procedure, one simple, rapid and accurate method was developed for the determination of total mercury in urine samples The method is based on the ultrasound assisted degradation of organo-mercurials and organic matter in urine in the presence of KMnO4/HCl/Focused Ultrasound. The procedure can be accomplished within 3 min, using 50% sonication amplitude provided by a probe ultrasonic device (63 W maximum output power, 22.5 kHz frequency). The method was applied to measure the mercury content in spiked urine from different non-exposed volunteers.