The Determination of Total Carbon Dioxide in Water

1. The method described involves extraction of the dissolved gas from an acidified sample in a modified van Slyke apparatus, and measurement of the electrical resistance of a standard sodium hydroxide solution before and after equilibration with the extracted gas. 2. The original sample must be not less than about 30 ml. for which a 10 ml. sample is drawn into the extraction apparatus. 3. There is a linear relation between the resistance finally measured and the total carbon dioxide content of the original sample up to a maximum determined by the strength of the standard hydroxide solution, which is thus adjusted to the desired range of carbon dioxide concentration, e.g. 0.005N-NaOH for 0-50 mg./l. and 0.02N for 0-200 mg./l. CO2. 4. The method is easily sensitive to 0.3 mg./l. in the range 0-50 mg./l. total carbon dioxide and about 1 mg./l. in the range 0-200 mg./l. With a rigidly standardized procedure increased accuracy was obtained so that replicate determinations on standard solutions in the 0-50 mg./l. range did not differ by more than 0.16 mg./l. 5. Precautions for handling samples containing carbon dioxide in solution prior to determination have been suggested. 6. About 15-20 min. are required for each determination and to Mrs D. E.