Measuring insulin in human vitreous humour using LC-MS/MS

Besides its particular importance as a widely used therapeutic agent, insulin (and its synthetic derivatives) has been suspected, purported, and proven to be a lethal weapon in numerous cases of attempted or successful homicide and suicide. In addition to blood and urine as common matrices for clinical diagnosis and post-mortem analysis, vitreous humour has gained considerable attention in autopsy and follow-up investigations due to its ability to provide valuable information on cause and time of death. However, post-mortem insulin analyses using such specimens have been rare due to the limited penetration of peptide hormones into the vitreous body, and immunoassays were exclusively employed in those studies. In the present communication, the determination of insulin(s) from vitreous humour by means of immunopurification combined with ultrahigh performance liquid chromatography--high resolution/high accuracy (tandem) mass spectrometry is reported. Exploiting the constantly increasing sensitivity and robustness of modern mass-spectrometry-based instruments, the option to identify insulin in post-mortem vitreous samples is demonstrated with a specimen collected from a non-diabetic victim who died from an insulin overdose. This communication represents the first successful mass-spectrometry-based analysis of post-mortem material related to an insulin poisoning case.