Greener analytical method for determination of thiomersal (sodium ethylmercurithiosalicylate) in ophthalmic solutions using sono-induced cold vapour generation-atomic absorption spectrometry after UV/H2O2 advanced oxidation

Abstract

A new method is described for the determination of thiomersal (i.e., a stabilizing agent) in eye-drop solutions by sono-induced cold vapour generation-atomic absorption spectrometry following an UV/H₂O₂ 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 μL of H₂O₂. 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 μg mL⁻¹ of thiomersal and the between-batch precision expressed as relative standard deviation for n = 4 separate UV oxidations ranged from 3 to 7%.