This work presents the development of an analytical method for sample preparation aiming at the K determination in silicate rocks (basalt, monzogranite and shale fines) following ultrasound dissolution and analysis by F AES. Sample preparation method was optimized by using fractional factorial designs. The following optimal conditions were obtained for each silicate rock: 0.1 g of sample mass for any of the three samples, and volumes of HNO3, HCl and HF, respectively, of 2.5, 0.8 and 2.5 mL for basalt; 3.5, 0.8 and 2.5 mL for monzogranite, and 2.5, 1.0 and 2.0 mL for shale fines. Sample dissolution was achieved by using the ultrasound bath at room temperature (25 °C) for 1 hour. The accuracy was evaluated through the analysis of two certified reference materials, for which there was no statistical difference between the certified and the found K concentration values (95% confidence level). The K concentrations determined were: 1.45 ± 0.01 for basalt; 4.19 ± 0.03 for monzogranite and 1.60 ± 0.02 for shale fines. The developed method presented accurate and reliable results for K amounts in silicate rocks and is simple and safe, which are important features for the implementation of a methodology as a routine analysis.

Um método simples e robusto para a determinação de arsênio em sedimentos por espectrometria de absorção atômica com geração de hidreto (HG-AAS) usando a amostragem em suspensão é proposto. Água régia (5% v/v) e ácido fluorídrico (1% v/v) foram misturados a uma alíquota do sedimento com tamanho de partícula 50 µm e colocados no banho ultra-sônico por 30 min. A suspensão foi deixada em repouso por 48 h para uma extração eficaz do analito para a fase aquosa. O volume final da suspensão foi ajustado com HCl 1 mol L-1. Uma solução de NaBH4 estabilizada com NaOH foi usada como agente redutor. A arsina foi transportada ao tubo T de quartzo aquecido a 900 °C para detecção. Cinco materiais de referência certificados de sedimento foram analisados e as concentrações obtidas foram concordantes com os valores certificados, de acordo com o teste-t para um nível da confiança de 95%, com RSD (desvio padrão relativo) menor que 13%. O limite de detecção (LOD) na amostra foi de 0,6 µg g-1. O procedimento proposto para a determinação de arsênio em sedimentos é preciso, exato e adequado para a análise de rotina de amostras ambientais.

A simple and robust method for the determination of arsenic in sediments by hydride generation atomic absorption spectrometry (HG-AAS) using slurry sampling is proposed. Aqua regia (5% v/v) and hydrofluoric acid (1% v/v) were mixed with an aliquot of the sediment with particle size of 50 µm in an ultrasonic bath for 30 min. The slurry was allowed to stand for 48 h for an effective extraction of the analyte to the aqueous phase. The final volume of the slurry was made up with HCl 1 mol L-1. A NaBH4 solution stabilized with NaOH was used as reducing agent. The arsine was transported to the quartz T-tube heated at 900 °C for detection. Five certified reference materials of sediment were analyzed and the obtained concentrations were in good agreement with the certified values, according to the t-test for a 95% confidence level with RSD (relative standard deviation) lower than 13%. The limit of detection (LOD) in the sample was 0.6 µg g-1. The proposed procedure for arsenic determination in sediment is precise, accurate and adequate for the environmental samples routine analyses.