Dielectric barrier discharge-plasma induced vaporization for the determination of thiomersal in vaccines by atomic fluorescence spectrometry

Abstract

Direct determination of thiomersal in vaccine by atomic fluorescence spectrometry with dielectric barrier discharge (DBD)-plasma induced vaporization was developed. No sample pretreatments other than dilution were needed in the measurement. The evaporation and atomization of thiomersal in vaccine samples was achieved rapidly in one step. The produced mercury vapor was transported to atomic fluorescence spectrometry for analysis. It is a green method that obviates the need of strong oxidization procedure for degradation of thiomersal to inorganic mercury and reduction agents such as sodium tetrahydroborate(III) or tin(II) chloride to generate Hg vapor. The DBD plasma was generated in a quartz tube (i.d. 5 mm and o.d. 6 mm) by a concentric circles model. The operating parameters such as discharge gas type, gas flow rate, and power were optimized. Possible interference by concomitant elements was also investigated. External calibration was achieved with aqueous standards solution of thiomersal. Under the optimal experimental condition, the detection limit was 0.03 μg L⁻¹ for Hg, equivalent to 0.06 μg L⁻¹ of thiomersal in solution. The analytical precision, represented by the relative standard deviation (RSD) from multiple measurements (n = 5) of 5 μg L⁻¹ thiomersal (as Hg), was 2.5%. This method was also applied to measure thiomersal in five commercial vaccines. In the absence of CRMs for thiomersal in vaccine samples, it was validated by comparing with results from inductively coupled plasma mass spectroscopy (ICP-MS), which showed good correlation.