Capillary electrophoresis-electrospray mass spectrometry for the analysis of recombinant bovine and porcine somatotropins

Abstract

A Beckman P/ACE 2050 high-performance capillary electrophoresis (HPCE) instrument has been interfaced with a Vestec electrospray ionization (ESI) mass spectrometer for the analysis of recombinant proteins. Peak resolution is not compromised by coupling HPCE to an ESI mass spectrometer. Recombinant bovine and porcine somatotropins (rbSt and rpSt) were used as model proteins. The standard curve of the capillary zone electrophoresis (CZE) method with UV detection for the determination of rpSt is linear in the range of 7-300 fmol with theoretical plates of approximately 410,000 m-1. The relative standard deviation for the rpSt peak migration time is less than 1%. The multiply-charged ion clusters obtained in the CZE-ESI mass spectrum for a sample of rpSt ranged from mlz 1363.2 (the cluster with 16 charges) to 1982.5 (the cluster with 11 charges). The average molecular weights of 21,812.6 and 21,798.3 for a sample of rbSt and rpSt determined in this study were nearly identical to the theoretical values of 21,812.0 and 21,797.9, respectively. Detection limit of the CZE-ESI mass spectrometer is approximately 100 fmol. The CZE method separated mono- and dideamidated species and monoacetylated compounds while the ESI mass spectrometer detected an analogue and a truncated homologue of rpSt comigrating with the major peak. The presence of mono- and dioxidized homologues was also detected in the major peak of some rbSt and rpSt samples. These data clearly indicated that, individually, both CZE and ESI mass spectrometric methods could not detect all impurities. Coupling of the HPCE Instrument and the ESI mass spectrometer enhances analytical capabilities of both tools for rapid characterization of recombinant proteins.