A time-based flow injection–cold vapor–atomic absorption spectrometry system with on-line microwave sample pre-treatment for the determination of inorganic and total mercury in urine

Abstract

A time based injection system used in conjunction with cold vapor generation atomic absorption spectrometry and microwave-aided heating oxidation with potassium persulfate has been developed for the determination of total and inorganic mercury in urine samples. Inorganic mercury is determined after reduction with SnCl 2 while total mercury is determined after an on-line oxidation step with persulfate prior to the reduction step to elemental mercury with SnCl 2. The difference between total and inorganic mercury determines the organomercury content in samples. Experimental parameters were optimized by the univariate optimization method. A linear calibration graph was obtained in the range 0.2–20 μg l −1 of Hg 2+ by using injection times from 0 to 12 s of a solution of 20 μg l −1 of either inorganic or organic mercury. The detection limit based on 3 σ of the blank signal was 0.1 μg Hg l −1 regardless of the mercury species under evaluation. The relative standard deviations for five independent measurements were 1.5% and 1.0% for total and inorganic mercury. The recoveries of different amounts of inorganic and organic mercury added to urine samples ranged from 98.5% to 102.2% and from 97.0% to 103%, respectively. Good agreement with certified values of the total mercury containing urine reference materials were also obtained. With the proposed procedure, 20 urine samples of unexposed subjects from Mérida city were measured; and the values lay in the range between 1.8 and 6.7 μg l −1. In addition, the use of a mercury standard solution as the carrier converts the flow injection manifold used in this work to an on-line standard addition system which permits a rapid and simple test for monitoring the mercury levels in these samples.