A new cold vapor technique within the context of green chemistry is described for determination of mercury in liquid samples following high-intensity ultrasonication. Volatile Hg evolved in a sonoreactor without the use of a chemical reducing agent is carried to a quartz cell kept at room temperature for measurement of the atomic absorption. The mechanism involved lies in the reduction of Hg(II) to Hg(0) by reducing gases formed upon sonication and subsequent volatilization of Hg(0) due to the degassing effect caused by the cavitation phenomenon. Addition of a low molecular weight organic acid such as formic acid favors the process, but vapor generation also occurs from Hg solutions in ultrapure water. The detection limit of Hg was 0.1 microg/L, and the repeatability, expressed as relative standard deviation, was 4.4% (peak height). Addition of small amounts of oxidizing substances such as the permanganate or dichromate anions completely suppressed the formation of Hg(0), which confirms the above mechanism. Effect of other factors such as ultrasound irradiation time, ultrasound amplitude, and the presence of concomitants are also investigated. Some complexing anions such as chloride favored the stabilization of Hg(II) in solution, hence causing an interference effect on the ultrasound-assisted reduction/volatilization process.
A new method is described for the determination of thiomersal (i.e., a stabilizing agent) in eyedrop solutions by sono-induced cold vapour generation-atomic absorption spectrometry following an UV/H 2 O 2 advanced oxidation process. A green methodology has been developed that eliminates the need for both strong oxidising conditions for degradation of thiomersal and conventional chemical reducing agents, such as tin chloride or sodium tetrahydroborate(III), for cold vapour generation. Conversion of thiomersal into Hg(II) is performed under 10 min UV irradiation of the eye-drop solution in the presence of 100 mL of H 2 O 2 . Sono-reduction of Hg(II) to yield Hg(0) is carried out in a batch reactor coupled to a quartz furnace atomizer kept at room temperature for measurement of the Hg atomic absorption. This reduction/vaporization process was enhanced by addition of formic acid to the sample solution prior to ultrasound irradiation. The method has been applied to the determination of thiomersal in seven commercial eye-drop solutions. The limit of detection was 0.04 mg mL À1 of thiomersal and the between-batch precision expressed as relative standard deviation for n ¼ 4 separate UV oxidations ranged from 3 to 7%.
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