Comparability assessment of the results of thiomersal quantification in adsorbed immunobiological medicinal products by colourimetry and by cold vapor atomic absorption spectrometry

Abstract

To ensure the quality of immunobiologicals, it is required to quantify the thiomersal preservative present in a number of them. The authors have previously developed an analytical procedure for thiomersal quantification in non-adsorbed immunobiological medicinal products, which is based on cold vapor atomic absorption spectrometry (CV AAS). The aim of the study was to analyse the possibility of using the CV AAS procedure for thiomersal content determination in adsorbed immunobiologicals and evaluate the comparability of thiomersal quantification results obtained by colourimetry and CV AAS. Materials and methods: the study used the national reference standard of mercury ions content and the pharmacopoeial reference standard of thiomersal content in adsorbed medicinal products (PhRS 3.1.00427), as well as samples of immunobiologicals by different manufacturers: a DTP vaccine, anatoxins, hepatitis B and influenza vaccines, and combined vaccines. The study involved CV AAS and the colourimetric reaction between mercury and dithizone. Results: the specificity of the CV AAS procedure is demonstrated by the coefficient of variation (3.95%) and the coefficient of correlation between the test sample volume and thiomersal content (0.9956). The regression analysis and the Fisher’s test value of 0.16 indicate the absence of bias. The trueness of the method is satisfactory, as the percent recovery differs from the total spiked amount by less than 10%. For the sensitivity of the CV AAS procedure, its quantification and detection limits are 6.9×10-3 μg/ mL and 2.3×10-3  μg/ mL, respectively. The Fisher’s test value obtained in the comparability assessment of the results of thiomersal quantification by colourimetry and CV AAS (1.29) is lower than the conventional tabulated one (3.96). Conclusions: according to the study, it is possible to use the CV AAS procedure for thiomersal quantification in adsorbed immunobiologicals. The established detection limit allows evaluating residual amounts of thiomersal in in-process intermediates during the production of preservative-free immunobilogical dosage forms. The comparability assessment of the results of thiomersal quantification by colourimetry and CV AAS, carried out using oneway ANOVA and Fisher’s test, showed the possibility of using PhRS 3.1.00427 to control the consistency of operation when reproducing the CV AAS procedure.