Matrix-assisted Laser Desorption/ionization In-Source Decay Mass Spectrometry Analysis of Human Insulin and Insulin Analogues for the Identification of Insulin from Insulin Preparations

The identification of human insulin and insulin analogues is necessary in forensic investigations. However, there is no quick and accurate method to identify them (components from insulin preparations). In this study, we aimed to develop a method to elucidate differences in amino acid sequences among human insulin and six insulin analogues. The mass spectra of seven insulin preparations were measured using the in-source decay method in matrix-assisted laser desorption/ionization (MALDI-ISD) with 1,5-diaminonaphthalene MALDI matrix. The mass spectra measured in the spiral mode yielded a series of c ion peaks that reflected the amino acid sequence in the C-terminus of the insulin B-chain and could discriminate the seven insulin preparations. The MALDI-ISD method is a rapid and convenient approach to identify human insulin and six insulin analogues that are components of all insulin preparations sold in Japan. In particular, this method can discriminate human insulin from insulin lispro, both of which have identical molecular weights, and therefore identifying them is difficult using conventional methods.