CONTINUOUS-FLOW METHOD FOR THE DETERMINATION OF TOTAL INORGANIC CARBONATE IN WATER

A double-tube separation system with an inner tube of microporous PTFE and an outer tube of PTFE is proposed for the continuous determination of total inorganic carbonate (TIC) in natural waters. Carbon dioxide produced by mixing a sample with 0.5 M sulphuric acid in the outer tube permeates through the microporous PTFE wall and dissolved in 5 mM sodium hydroxide solution in the inner tube. The inner stream passes two electrical conductivity (EC) detectors, one before and the other after the double-tube separator, and TIC in the sample is measured as the difference in the signals obtained from the two detectors. The relative electrical conductivity was proportional to the concentration of TIC in the range 5 X 10(-5)-5 x 10(-3) M. The limit of detection (signal-to-noise ratio = 3) was 1.0 x 10(-5) M. The time required for a 98% response was 2 min. Sulphide interfered but was completely decomposed by using chromate. The method was applied to the determination of TIC in lake waters.