Ion chromatography of magnesium, strontium, calcium and barium ions using a metallic copper electrode as a potentiometric detector

The determination of inorganic cations by high-performance liquid chromatography (HPLC) has received increased attention over recent years and when compared with most conventional spectroscopic methods, HPLC offers the considerable advantage of allowing a number of cations to be determined in a single run. This approach has been successfully used for the determination of alkali metal and ammonium ions, alkaline earth metal ions, transition metal ions and lanthanides. These methods have been based on ion-exchange or ion-pairing separation techniques, coupled with conductivity, coulometric or spectrophotometric detection. In the latter case, detection was accomplished by a post-column reaction system wherein coloured metal complexes were formed. An important disadvantage of such a post-column reaction detector is the band broadening which inevitably results in the mixing coil. We have previously described a potentiometric HPLC detector based on an active copper surface as the sensing electrode. This device was originally applied to the direct detection of copper complexing ligands such as amino acids, but we also recently reported its application in flow-injection analysis to the indirect detection of cations in a suitable carrier. The aim of this communication is to indicate the utility of potentiometric detection in cation chromatography as an alternative to presently used detection methods.