Determination of thimerosal in human and veterinarian vaccines by photochemical vapor generation coupled to ICP OES

Abstract

A simple and fast method is described for the determination of Hg, present as thimerosal, in vaccines by photochemical vapor generation coupled to axial view inductively coupled plasma optical emission spectrometry. Mercury emission was detected at 253.652 nm. No sample treatment was necessary other than simple dilution and addition of 10% v/v formic acid. Vapor generation conditions were optimized and included formic acid concentration, sample flow rate, reactor tube dimensions and argon flow rate. External calibration was achieved using aqueous standard solutions of Hg²⁺ containing 10% v/v formic acid. The detection limit (3 s, n = 10) was 0.3 µg L⁻¹ of Hg or 0.6 µg L⁻¹ of thimerosal in solution, equivalent to 60.0 µg L⁻¹ of thimerosal in the original vaccine solution or 0.03 µg of thimerosal per dose. The procedure was applied to the analysis of anti-rabies, diphtheria/tetanus, hepatitis B and influenza vaccines, sourced from two producers. Thimerosal was present in the vaccines within a narrow range of 47.4 ± 0.4 to 53.7 ± 0.7 µg per dose (0.5 mL vaccine), in agreement with product information, except for the influenza vaccine from one of the producers, for which the thimerosal mass per dose was below the detection limit. Recoveries of 93–102% demonstrated the robustness of the methodology. Precision, expressed as relative standard deviation, yielded 2.9% under conditions of repeatability and 4.4% for reproducibility. This simple procedure is currently adopted by Tecpar (Curitiba, Brazil) to control the amount of thimerosal in anti-rabies vaccines.