Determination of thiomersal by flow injection coupled with microwave-assisted photochemical online oxidative decomposition of organic mercury and cold vapor atomic fluorescence spectroscopy

• Thiomersal was determined on line using FI-MW/UV-CVGAFS.
• MW/UV allows a “green” on line oxidation of organic mercury to HgII.
• Each measure requires less than 5 min with a LOD of 3 ng mL−1 (as mercury).
• Hg concentration in commercial ophthalmic solutions ranges between 7.5 and 59.0 μg mL−1.

We developed a flow injection (FI) method for the determination of thiomersal (sodium ethylmercurithiosalicylate, C9H9HgNaO2S) based on the UV/microwave (MW) photochemical, online oxidation of organic mercury, followed by cold vapor generation atomic fluorescence spectrometry (CVG-AFS) detection. Thiomersal was quantitatively converted in the MW/UV process to Hg(II), with a yield of 97 ± 3%. This reaction was followed by the reduction of Hg(II) to Hg(0) performed in a knotted reaction coil with NaBH4 solution, and AFS detection in an Ar/H2 miniaturized flame. The method was linear in the 0.01–2 μg mL−1 range, with a LOD of 0.003 μg mL−1. This method has been applied to the determination of thiomersal in ophthalmic solutions, with recoveries ranging between 97% and 101%. We found a mercury concentration in commercial ophthalmic solutions ranging between 7.5 and 59.0 μg mL−1.

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