Online Affinity Assessment and Immunoaffinity Sample Pretreatment in Capillary Electrophoresis-Mass Spectrometry

Capillary electrophoresis (CE) has emerged as a very useful technique for the analysis of a variety of components ranging from small ions to large biomolecules. CE provides efficient separations and short analysis times, and allows compound analysis under near-physiological conditions. In the early 1990s of the last century the capability of CE to assess biomolecular affinity interactions was demonstrated and coined affinity capillary electrophoresis (ACE). In the same time, the use of affinity materials for selective online extraction of compounds before CE analysis was established. This immunoaffinity (IA) CE approach aims for highly specific isolation and preconcentration of target analytes from a biological matrix. Currently, both ACE and IA-CE have developed into proven analytical approaches. Over the last two decades, CE coupled to mass spectrometry (MS) has been demonstrated to be a powerful hyphenated technique, combining the high separation efficiency of CE with the selectivity of MS. MS has also been introduced as a detection technique for both ACE and IA-CE. This chapter provides an overview of the developments and applications in ACE-MS and IA-CE-MS. First, the basic aspects of CE, ACE, and IA-CE are introduced. Subsequently, the hyphenation of CE and MS detection is treated, specifically highlighting aspects that are important for affinity determinations. The setup and performance of reported ACE-MS and IA-CE-MS methods are treated systematically and orderly tables summarizing practical aspects of each method are provided. The application of ACE-MS and IA-CE-MS is outlined treating typical examples, such as peptide library screening, study of protein-ligand interactions, and bioanalysis of peptides and proteins.