Evaluation of acoustic emission as a means for carbonate determination

A method is described for the determination of total carbonate by means of acoustic emission. Acoustic signals are generated from effervescence of carbon dioxide when aqueous samples containing carbonate or hydrogencarbonate are acidified. Two approaches are evaluated. The first involves direct mixing of carbonate and acid streams in a flow system. Detection limits around 0.1 M are observed with this arrangement. In the second approach, the flow system is used to preconcentrate the carbonate species onto an anion exchange column prior to acidification. Limits of detection below 3.5 pmol of carbonate are achieved with this method (1 mM hydrogencarbonate at a flow rate of 1 ml min-’ for 3.5 mm). Sensitivity is found to be optimum when a glass frit is placed in-line and the acid flow is opposite to that of the carbonate. Calibration curves are nonlinear for both the direct and preconcentration methods. Limitations of the proposed methods are discussed.