Sensitive and fast identification of urinary human, synthetic and animal insulin by means of nano-UPLC coupled with high-resolution/high-accuracy mass spectrometry

The double-chain polypeptide insulin and its synthetic (Insulin Glulisine, Insulin Aspart, Insulin Glargine, or Insulin Lispro) or animal analogues (porcine insulin or bovine insulin) are potential performance-enhancing agents in elite sports or potentially effective toxins in forensic science.The present study demonstrates an analytical method to purify the insulins simultaneously from urine specimens with an approach based on immunoaffinity isolation, using coated magnetic beads (anti-mouse) and a primary anti-insulin antibody (IgG, monoclonal). The extracts were purified sufficiently for separation by means of nano-flow liquid chromatography coupled with nano-scale high-resolution, high-accuracy ESI-MS/MS. Elucidation of collision-induced dissociations with product ion experiments using the fivefold protonated precursor ion of each target analyte enabled all synthetic and animal insulins to be differentiated from their human counterpart, which was particularly important for Lispro, possessing the same molecular mass as human insulin.The method was fully validated for specificity, limit of detection (LOD, 0.5 fmol/mL), precision (<20%), recovery (approximately 30%) and linearity (2-40 fmol/mL) for all target analytes.