The Determination of Total Carbon Dioxide in Water

Abstract

ABSTRACT 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. The original sample must be not less than about 30 ml. for which a 10 ml., sample is drawn into the extraction apparatus. 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 ·005 N-NaOH for 0 –50 mg./L and 0 ·02 N for 0 –200 mg./l. CO2. 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. Precautions for handling samples containing carbon dioxide in solution prior to determination have been suggested. About 15 –20 min. are required for each determination and to Mrs D. E..