Non-aqueous liquid chromatography of some metalloporphyrins on a reversed-phase column

The effect of the hetaerons tetraphenylarsonium chloride (Ph4AsCl) and tetraphenylarsonium perchlorate (Ph4AsClO4) on the retention of neutral and cationic metalloporphyrins on a reversed-phase column with an acetonitrile-tetrahydrofuran (85:15, v/v) mobile phase was investigated. The adsorption properties of the two hetaerons on the stationary phase were dramatically different. While Ph4AsCl adsorbed, reaching saturation at a concentration of 4 mM, Ph4AsClO4 did not adsorb. The retention of neutral metalloporphyrins was unaffected, while cationic metalloporphyrins demonstrated decreasing retention with an increase in the concentration of either hetaeron. The possible equilibria involved are discussed.