Ultrasound-assisted extraction for mercury speciation by the flow injection-cold vapor technique

Abstract

A simple and rapid ultrasound-assisted extraction method with hydrochloric acid for mercury speciation in fish tissues was developed. Centrifuged extracts were directly injected into a flow injection-cold vapor atomic absorption spectrometry system. First, methylmercury was separately determined using sodium tetrahydroborate as reducing agent after selective extraction with 2 mol dm ^–3 hydrochloric acid. Second, inorganic mercury was determined by selective reduction with stannous chloride in 5 mol dm ^–3 hydrochloric acid extracts containing both mercury species. Total mercury could not be determined in the sonicated acid extracts using sodium tetrahydroborate as reducing agent because the methylmercury and inorganic mercury sensitivities were different. The detection limit was 11 and 5 ng g ^–1 for methylmercury and inorganic mercury, respectively. The recovery was >92% and the precision (RSD) ranged from 5 to 10% for three replicates of each sample analyzed by the standard additions method. Total mercury, calculated as the sum of methylmercury and inorganic mercury, was in agreement with the total mercury content determined after microwave digestion. The method was validated by means of three fish certified reference materials. The concentrations found were in good agreement with the certified values.