Gas diffusion flow injection determination of thiomersal in vaccines

A new simple gas diffusion flow injection method has been developed for the determination of thiomersal in biological samples. The method is based on cold vapor generation of monoatomic mercury from thiomersal reaction with acidic stannous chloride solution (0.6%) acting as reducing agent. The evolved mercury partially diffuses through a Teflon membrane into an acidic permanganate (2.25 × 10−4 mol L−1) acceptor stream, where it is oxidized and re-converted to Hg(II). The resulting decrease in acceptor stream absorbance is sensitively monitored at 528 nm. Flow injection variable parameters such as reagents concentrations, injected volume, reactor length, temperature and flow rate were carefully investigated and optimized. The concentration–response relationship was linear over a concentration range of 1–30 mg L−1 with a correlation coefficient greater than 0.99 and a good reproducibility (RSD < 1.42%, n = 6) at 10 mg L−1. A detection limit of 0.07 mg L−1 (S/N = 3) and a sampling frequency of 5 samples h−1 were obtained. The method was successfully applied for the determination of thiomersal in different types of vaccines and gave results in close agreement with those found by previously established HPLC method with no significant interference from vaccines matrices.