DEVELOPMENT OF A NEW METHOD FOR DIRECT MEASUREMENT OF (RHO)CO2 IN NATURAL-WATERS

A new direct measurement method for pCO2 in water samples is presented . The technique is based on the fact that the dissolved CO2 in a water sample is able to diffuse through the wall of a thin silicon rubber t ubing, whereas the dissolved ions remain. The CO2 passing through the wall is equilibrated with the deionized water flowing inside the tubin g, and its electric conductivity is measured by a conductivity flow ce ll afterward. Laboratory experiments on 255 CO2 standard samples with pCO2 varying from 300 to 30,000 ppmv show a mean CO2 exchange ratio R across the silicon rubber membrane of 0.95, with SD = +/-0.04. For pCO 2 in the 40-300 ppmv range (40 CO2-standard samples), a mean exchange ratio R = 0.93+/-0.09 has been determined. The detection limit of this method is 0.6 muM (approximately 18 ppmv at 25-degrees-C).