Ethylenediamine–hydrochloric acid–zinc(II) eluent for the suppressed ion chromatographic separation of strontium(II) from a large amount of calcium(II): application of the method to the simultaneous determination of magnesium(II), calcium(II) and strontium(II) in high salinity sub-surface waters

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Abstract
A new eluent has been developed for the suppressed ion chromatographic separation of strontium from large amounts of calcium. Together with a Dionex CS-2 separator column, the eluent, a mixture of 2.5 mmol dm–3 ethylenediamine, 5 mmol dm–3 hydrochloric acid and 1 mmol dm–3 Zn2+, was successfully used for the simultaneous determination of strontium, magnesium and calcium in high salinity sub-surface waters. The results of the determination of magnesium, calcium and strontium in sub-surface Arab-D brine and its mixtures with aquifer Wasia and sea-water compare well (p > 0.1) with those obtained by a standard atomic absorption spectrometric method. A base line separation of magnesium, calcium and strontium from each other and from a large excess of sodium in a sub-surface brine can be achieved in approximately 8.0 min. This is a considerably shorter time than that required to achieve a reasonably good separation factor between calcium and strontium by other liquid chromatographic methods, although such methods have not been used for the determination of alkaline earth metal cations in sub-surface waters.