Critical evaluation of the applicability of neutral carrier-based calcium selective microelectrodes

The performance of calcium ion-selective microelectrodes based on a neutral carrier for extra- and intra-cellular measurements of free Ca 2+ ions as reported in the recent literature is assessed. A novel membrane consisting of readily available components is presented which overcomes the technical problems associated with very fine electrode tips. Measured selectivity factors, log K pot CaM , for M 2+ = Na + , K + , and Mg 2+ are -5.5, -5.4, and