(1:1, v/v) was added to each tube and kept for 10 min at room temperature then close the tubes and placed in covered PTFE container. It was then heated following a one-stage digestion programmed at 80% of total power (900 W), 2–4 min were required for complete dissolution of all samples. The digestion tubes were cooled, and the resulting solution was diluted up to 10 mL with 0.2 M HCl. The prepared samples were stored in Teflon tubes as master sample solutions.
Mercury determination was carried out by cold vapor atomic absorption spectrometry (CVAAS), using sodium tetrahydroborate as reducing agent and hydrochloric acid as carrier solution. About 500 lL of the each stock sample solution of CRM, and real samples were transferred to the PTFE flasks of the MHS-15 system and 10 mL of a 0.15 M HCl solution were added, along with 40 lL of the antifoam agent. The system was sealed and 3% (m/v) NaBH
was added for 5s to the PTFE flask. A stream of high purity argon gas at a flow rate of 200 mL/min carried the Hg vapor generated in system to the quartz cell, and the signals of the generated Hg atoms were measured. Calibration was performed using aqueous standards (1–25 lg/L) and subjected to CV AAS procedure described above. The validity and efficiency of the microwave assisted digestion method was checked with certified values of CRM DORM -2, as reported in our previous work (Shah et al., 2009b).
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