Development of online microdialysis–microfluidic-based photocatalyst-assisted vaporization device–inductively coupled plasma-mass spectrometry hyphenated analytical system for in vivo quantification of the transition of brain extracellular mercury after thimerosal administration

•An online hyphenated analytical system with in vivo sampling and sample pretreatment was developed.•Detection limits achieved 2.7 and 1.7 ng L−1 in saline samples for methylmercury and thimerosal, respectively.•In vivo quantification of the transition of brain extracellular mercury was successfully performed.•The transition patterns of brain extracellular mercury after thimerosal administration were similar to that of methylmercury.