Prince:Strong Cation Exchange
Strong Cation Exchange separates compounds based on polarity and charge. More specifically strong cation exchange bind basic peptide (peptides with a positive charge) and neutral polar peptides. Non-polar and acidic polar peptides flow through the column and are collected. The column is then washed with very acidic solution to remove neutral polar peptides followed by a very basic wash to remove basic peptides. The peptides are now separated into three different fractions for mass spectrometry.
Figure: 1. A column is normally used for SCX. The beads in the column contain acidic groups which bind to basic peptides. The column is loaded with a solution of peptides. 2. This is the acidic group bound to the Si beads. There are two different kinds of interactions taking place. The first is an interaction between the negatively charged sulfate group and the positively charged resin. The second is a hydrogen bonding interaction between the silicon resin and neutral polar peptides. Neutral polar peptides are removed from the resin by washing with concentrated acid. The acid has a stronger affinity for the silica resin than the neutral polar peptides have for the silica resin, so the peptides are released from the silica and washed from the column. Basic peptides are removed from the column using a basic solution. Again the basic solution has a greater affinity for the negatively charged sulfate causing the basic peptides to be released and washed from the column.