COMPARISON OF PHOTOMETRY AND CONDUCTOMETRY FOR THE DETERMINATION OF TOTAL CARBONATE BY GAS PERMEATION FLOW-INJECTION ANALYSIS

The experimental system involves the permeative preconcentration of CO2 from an acidified sample through a tubular silicone rubber membrane into a suitable receptor. Procedures for measuring the CO2 collected in the receptor by the absorbance change of an acid-base indicator incorporated in the receptor or by the conductance change of the receptor are compared. Previous theoretical considerations of the photometric system are augmented for numerical modeling and the theoretical behavior of the conductometric system is considered in detail. Experimental data generally conform to theoretical expectations. Based on either reproducibility or sensitivity, the conductometric measurement method using a solution of 1-10mM tris(hydroxymethylamino)methane as receptor is recommended. The interference from sulfite or sulfide can be eliminated by adding acidic permanganate to the sample; considerably more involved arrangements are necessary to eliminate interferences from cyanide.