Carrier ampholyte-free free-flow isoelectric focusing for separation of protein

Free-flow isoelectric focusing (FFIEF) has the merits of mild separation conditions, high recovery and resolution, but suffers from the issues of ampholytes interference and high cost due to expensive carrier ampholytes. In this paper, a home-made carrier ampholyte-free FFIEF system was constructed via orientated migration of H⁺ and OH^- provided by electrode solutions. When applying an electric field, a linear pH gradient from pH 4 to 9 (R² = 0.994) was automatically formed by the electromigration of protons and hydroxyl ions in the separation chamber. The carrier ampholyte-free FFIEF system not only avoids interference of ampholyte to detection but also guarantees high separation resolution by establishing stable pH gradient. The separation selectivity was conveniently adjusted by controlling operating voltage and optimizing the composition, concentration and flow rate of the carrier buffer. The constructed system was applied to separation of proteins in egg white, followed by MADLI-TOF-MS identification. Three major proteins, ovomucoid, ovalbumin and ovotransferrin, were successfully separated according to their pI values with 15 mmol/L Tris-acetic acid (pH = 6.5) as carrier buffer at a flow rate of 12.9 mL/min.