Ultrasound assisted extraction for the determination of mercury in sediment samples employing cold vapour atomic absorption spectrometry

Abstract

An extraction procedure involving ultrasound assisted radiation was proposed for the determination of mercury in river sediment samples using cold vapour atomic absorption spectrometry (CV AAS). The optimization step was performed using a two-level full factorial design, being that the studied factors were thiourea and hydrochloric acid concentrations, time and temperature of sonication and absorbance as the chemometric response. The experimental conditions of the extraction procedure found by optimization were as follows: hydrochloric acid concentration, 4 mol L⁻¹; thiourea concentration, 0.75% (m v⁻¹); sonication time, 20 min and sonication temperature, 60 °C. The validation studies demonstrated that by employing the optimized conditions, the method allows the determination of mercury using an external calibration technique with limits of detection and quantification of 10 and 35 ng L⁻¹, respectively, and precision expressed as a relative standard deviation of 4.31% for a mercury solution with a concentration of 5.00 μg L⁻¹. The limits of detection and quantification calculated for a sample mass of 0.20 g are respectively 1.04 and 3.46 ng g⁻¹. The method accuracy was confirmed by analysis of the certified reference materials: NIST SRM 2709a San Joaquim Soil and BCR 320 Channel sediment. This method was applied for the determination of mercury in five sediment samples collected from the São Paulo River (Bahia State, Brazil). The mercury concentrations obtained varied from 13.8 to 38.5 ng g⁻¹. These values are compatible with other data reported in the literature for mercury contents in uncontaminated sediment samples.