Chapter 2: How to Couple and Handle Liquid Chromatography with Mass Spectrometry

In the last two decades the coupling of high-performance liquid chromatography (HPLC or LC) with mass spectrometry (MS) has become very efficient by using a connection via atmospheric pressure ionization (API) sources. In principle, various API techniques in combination can now transfer almost all molecules from the liquid phase into the gasphase as ions. The resulting ionic species can easily be guided by electric fields into the mass spectrometric analyser. Proteins and peptides are typically sprayed by electrospray ionization (ESI) due to the inherent soft conditions. Atmospheric pressure chemical ionization (APCI) is a complementary technique for ionizing small molecules of low polarity, but is rarely used for protein and peptide ionization.

This chapter focuses on these two ionization techniques (ESI and APCI) and presents examples and information about the correct decision and application of ionization sources coupled to adequate chromatographic separation and mass spectrometric detection techniques.