Chelates of cobalt(III) and iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol as test probes for the characterization of chromatographic effects on a reversed-phase liquid chromatography stationary phase

The chromatographic effects on a reversed-phase liquid chromatography (RPLC) phase were established with the use of chelates system: cobalt(III) and iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol as the test probes. Both chelates have the same octahedral structure, M:L = 1:2, the former chelate is cationic and can be used to probe the ion-exchange phenomena on a RPLC phase, whereas the latter is not charged and can be used as reference molecule with respect to the charged one. Based on well-established LC phenomena referred in the literature, the suitability of the chelate system for examining some chromatographic effects was tested. It was concluded that the proposed test method is sensitive towards the ion-exchange phenomena on the LC phase and the hydrogen bonding between the solvent eluent and the LC phase. In addition, chromatographic effects due to the presence of ultrasonic field or due to the presence of aromatic amines in the eluent were observed with the help of the proposed test method. Based on molecular computation, the properties of chelates were compared with properties of quaternary amines, the probes most frequently used for testing LC phases, and the possible differences in an interaction of the mentioned compounds with a surface of a RPLC phase were indicated.