Reversed phase chromatographic separations of cationic and anionic metal complexes
Date
1987
Authors
Hewavitharana, Amitha Kumudini
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Abstract
Separation of a variety of mixtures of cationic chromium(III) complexes and anionic cobalt(III) complexes by Ion-pair Reversed Phase HPLC is reported. Achieving separation, or rather improving the resolution of mixtures of highly charged anionic Co complexes, was of major concern.
To improve resolution, a number of mobile phase parameters are manipulated. They include changing the organic solvent composition, the length and the number of alkyl chains of the ion interaction reagent and the concentration of the ion interaction reagent. A higher concentration of organic solvent improves the resolution by narrowing the peaks, but the other two parameters do not change the resolution significantly.
Resolution is further improved by minimising peak tailing through masking of the active sites on the stationary phase. For this, a competing ion is incorporated in the above method. In this way a dramatic improvement in resolution is achieved within very short elution times and with very low amounts of organic solvent in the eluent. This method gives complete separation of anionic Co complex mixtures but has failed so far to separate geometrical isomers.
The effect of the nature and the concentration of the competing ion on resolution is also investigated. Peak splitting is observed with higher concentrations of the competing ion in the eluent. Finally, the effect of the temperature and the sample size on peak splitting is studied.