There are two viable options for analysis of iron (II) and iron (III) by CE.
Option 1. Add EDTA and analyze the iron-EDTA complexes. Use the CElixir OA Kit because the complexes will be anionic.
Option 2. Use off-line selective complexation of the iron (II) and (III) species and perform the analysis by MEKC. Use the CElixir SDS Kit in this case. Takagai & Igarashi describe the process in a research article available here. This was reported to be the most effective method to achieve separation of the two analytes.
Option 3. Use an Imidazole-Acetic acid buffer, pH4. You may not get separation of Fe(II) and Fe(III) but there will be CE migration. This buffer is however not supplied by MicroSolv.