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 CO 2 from an acidified sample through a tubular silicone rubber membrane into a suitable receptor. Procedures for measuring the CO2 collected i n the receptor by the absorbance change of an acid-base indicator inco rporated in the receptor or by the conductance change of the receptor are compared. Previous theoretical considerations of the photometric s ystem are augmented for numerical modeling and the theoretical behavio r of the conductometric system is considered in detail. Experimental d ata generally conform to theoretical expectations. Based on either rep roducibility or sensitivity, the conductometric measurement method usi ng a solution of 1-10mM tris(hydroxymethylamino)methane as receptor is recommended. The interference from sulfite or sulfide can be eliminat ed by adding acidic permanganate to the sample; considerably more invo lved arrangements are necessary to eliminate interferences from cyanid e.