Quantification of serum C-peptide by isotope-dilution liquid chromatography–tandem mass spectrometry: Enhanced detection using chemical modification and immunoaffinity purification.

Highlights: [•] We developed a highly sensitive method for quantification of serum C-peptide. [•] This method is based on isotope-dilution mass spectrometry. [•] We applied chemical modification and immunoaffinity purification to this method. [•] These resulted in a 23-fold enhancement of the sensitivity. [•] This method enables high sensitivity and precision covering the reference interval. [ABSTRACT FROM AUTHOR]