New design of cold finger for sample preparation in open system: Determination of Hg in biological samples by CV-AAS

Abstract

This paper presents studies involving the determination of Hg in biological samples by cold vapor atomic absorption spectrometry (CV-AAS) using a simple and inexpensive system for sample digestion. The system consists of a glass tube that is closed with a small glass tube filled with cold water, which is called cold finger, and helps the recirculation of the acids within the bigger tube. The use of cold finger avoided the loss of analyte and the excessive evaporation of the acids during the heating. Thus, lower amount of acid was required, decreasing the risk of contamination. Studies of temperature of the digester block were performed with aqueous standard solutions in an interval between 80 and 120°C. No significant loss of analyte was observed when compared with the open system. Certified reference materials (CRMs) were used to evaluate the accuracy of the proposed methodology. For this process, samples were digested with HNO3 for 2h in a digester block between 90 and 120°C, using the open system with the cold finger. The use of the cold finger system was efficient with similar results to those expected for CRMs for mercury (Hg) concentrations. For the open system, loss of analyte was observed when the digestion temperature was increased. The limit of detection (LOD) was 0.08μgL−1. The digestion procedure using cold finger in an open system is useful, at boiling point solution temperature, safe and simple for Hg determination in biological samples. Moreover, it can be used as an alternative to microwave-assisted digestion.