The chromatographic performance of metal chelating analytes on a C18 functionalized styrene-divinylbenzene stationary phase is studied. The influence of metal ions impurities on their peak shapes and the metal sorption properties of such a stationary phase are investigated. Quantitative evidence is obtained to support the proposition that sorption of metal ions onto the stationary phase results in a chromatographic performance loss of the investigated metal chelating analytes. Since their retention is a function of strong complexing interactions and van der Waals forces, the mixed retention mechanism is best described as one of “metal interaction.” Also when the base material is itself strongly hydrophobic and displays no ionic character whatsoever, pure reversed phase interactions may not be always achievable.