Simultaneous determination of alkali and alkaline earth metals by ion chromatography with neutral carrier-based ion-selective electrode detector

Neutral carrier-based potentiometric detectors that can monitor both mono- and divalent cations have been developed for ion chromatography. The solvent polymeric membranes doped with a mixture of monesin methyl ester (MME; a monovalent cation-selective ionophore) and a divalent cation-selective ionophore (ETH 1117 or ETH 4030) have the combined properties of each single ionophore. These double ionophore-doped ISE membranes showed similar selectivities for ammonium, alkali and alkaline earth metal ions. The ion chromatograms of ten representative cations (Li+, Na+, NH+4, K+, Rb+, Cs+, Ca2+, Mg2+, Sr2+ and Ba2+) proved their practical utility. The MMEETH 1117 electrode, which showed better detection limits for most cations tested here and a longer lifetime (16 days), was further utilized for determining alkali and alkaline earth metal cations in commercial mineral waters. The results were in good agreement with those determined by using inductively coupled plasma atomic emission spectrometry.