Quantitative analysis of urinary C-peptide by liquid chromatography-tandemmass spectrometry with a stable isotopically labelled internal standard

We describe the first results of a quantitative LC-tandem mass spectrometry method for urinary C-peptide with the use of [H-2(14)]C-peptide as interna l standard. LC was based on gradient elution of a Hypersil PEP C-18 column. Mass spectrometry was performed in the negative electrospray ionization mo de and by monitoring of the transitions at m/z 1514/1334 ([H-2(14)]C-peptid e) and 1507/1320 (C-peptide). For sample preparation, we applied ultrafiltr ation. The analytical performance of the method in terms of measurement pre cision gave an RSD of <2% (n=10). The overall imprecision was investigated from independent analysis of two urine samples in six-fold and resulted in an RSD<5%. The limit of detection, expressed as signal-to-noise ratio 3, wa s similar to0.15 ng C-peptide injected. Analysis of 10 random urine samples from laboratory volunteers showed interference-free ion chromatograms at a signal-to-noise ratio of similar to 75 on average. The C-peptide concentra tions calculated from quantification by the bracketing calibration techniqu e ranged from 32 to 165 ng/ml. (C) 2000 Elsevier Science B.V. All rights re served.