Protein digest analysis by pressurized capillary electrochromatography using an ion trap storage/reflectron time-of-flight mass detector.

Pressurized capillary electrochromatography (pCEC) has been coupled to an ion trap storage/reflectron time-of-flight mass spectrometer for the analysis of peptide mixtures and protein digests. Taking advantage of the electroosmotic flow, high separation efficiency has been achieved in pCEC due to a relatively flat flow profile and the use of smaller packing materials. A supplementary pressure was used in these experiments which suppressed bubble formation and also allowed the tuning of the elution of peptides using the electrical field. In this work, a fast separation of a six-peptide mixture has been successfully performed. Using columns only 6 cm long, a tryptic digest of bovine cytochrome c was fully separated in around 14 min by properly tuning the applied voltage and the supplementary pressure. In addition, relatively complex protein digests, such as a tryptic digest of chicken ovalbumin, were analyzed using this pCEC/MS system, and more than 20 peaks were resolved in the total ion current chromatogram within 17 min. The use of an ion trap storage/reflectron time-of-flight mass spectrometer as an on-line detector further increased the resolving power of the pCEC by unambiguously identifying coeluting components. The nonscanning property of the time-of flight mass analyzer and the ion signal integration capability of the ion trap were successfully combined to provide rapid and sensitive full-mass range detection in these experiments.