Abstract: The system comprised a carrier stream of water or aqueous acidic solution, flowing through a cell containing a glass pH micro-electrode, and a syringe containing Dowex HGR-W2 ion-exchange resin, for exchange of metal ions for H+ for subsequent injection into the carrier stream. Two injections were made per sample, one before and one after ion exchange. The calibration graph was rectilinear for pH 1 to 5. The method was reasonably accurate, reproducible, rapid and simple. The method can be applied to determine a wide range of metal ion concentration. and can be made selective for one ion in the presence of others by pre-complexation. The method is applicable to study dissolution rate curves, and was applied to the dissolution of CaCO3 in H3PO4 as an example.