Colorimetric Method for Determination of Traces of Carbon Dioxide in Air NORMAN A. SPECTOR' AND BARh-ETT F. DODGE Yale University, New Haven Conn.
A colorimetric method for determining traces of carbon dioxide, using a Lumetron photoelectric colorimeter, depends on the decrease in color intensity of a solution of sodium hydroxide colored with phenolphthalein indicator. The alkalinity of the solution decreases as it absorbs carbon dioxide from the gas sample to be analyzed and consequently the depth of color decreases. The change in the amount of light which the solution transmits is made a measure of carbon dioxide concentration. The precision and sensitivity of the method are functions of the carbon dioxide concentration as well as the volumes of the gas sample and absorbing solution. In general the precision increases with increase in carbon dioxide concentration being measured, with the use of larger gas samples and, within limits, with the use of smaller volumes of absorbing solution. The accuracy of the results is considered to be of the same order as the precision. A 1-liter gas sample is sufficient to determine a carbon dioxide concentration in air of 0.0010% (10 p.p.m.) with a precision of 10%-i. e., +=0.00010/0. Apparatus and Solutions. A Lumetron photoelectric colorimeter, Model 402E, manufactured by the Photovolt Corporrttion, New York, X. Y., was used for the light transmission measurements. The instrument reads directly in per cent transmission. A 100-mm. cell was used with this instrument, requiring a solution volume of 80 cc. and providing a light path 100 mm. long.
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HE motive underlying the development of this analytical
method was its application to the removal of carbon dioxide from atmospheric air. Such removal is essential to the proper functioning of many processes, and the evaluation of absorption coefficients indicating the performance of equipment for this service requires a rapid and accurate determination of traces of carbon dioxide in the inlet and exit air streams. This paper presents the development of a method for accurately determining traces of carbon dioxide in air over the concentration range from 0.0315%, usually found in atmospheric air, down to 0.0005%. For this range ordinary gas analysis apparatus cannot be used and the gravimetric methods previously available required large volumes of gas and were too long and tedious. Analytical methods reported in the literature were re\
