Development of a fast method for direct analysis of intact synthetic insulins in human plasma: the large peptide challenge

Intact insulins are difficult to analyze by LC-MS/MS due to nonspecific binding and poor sensitivity, solubility and fragmentation. This work aims to provide a simpler, faster LC-MS method and focuses on solving the above issues. A novel charged-surface chromatographic column produced peak widths for insulin that were significantly narrower than traditional C18 columns when using formic acid as mobile phase. Mass spectral fragments m/z >700 provided greater specificity, significantly reducing endogenous background. Detection limits in human plasma were 0.2 ng/ml for insulin glargine, glulisine and detemir, and 0.5 ng/ml for insulin aspart. Average accuracy for standard curve and QC samples was 93.4%. A simple SPE LC-MS analysis was developed for direct, simultaneous quantification of insulin glargine, detemir, aspart and glulisine.