Gas Phase Chromatography--Study of the Gow-Mac Gas Density Balance--Application to Quantitative Analysis

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Abstract
The gas density balance invented by Martin (1) is one of the very first chromatographic detectors, but practical difficulties in its construction have prevented until recently any widespread utilization of this detector. The Gow-Mac balance, patented by Standard Oil Co. (Indiana, U.S.A.), is, on the other hand, of surprising simplicity and at the same time offers comparable performance. The purpose of the present study is to define the optimum operating conditions of the Gow-Mac balance, mounted on a chromatograph of our own construction. A systematic study of response as a function of the nature of the carrier gas and of flow rates shows that the highest sensitivities have been obtained with CO2, then with nitrogen, and finally with argon, using the largest possible ratio of Reference/Measuring flow rates, but with the Reference flow rate constant for a given carrier gas, i.e., 4 liter/hr. for CO2 and 6 liter/hr. for nitrogen and argon. The gas density balance gives the concentration in weight per cent of the different constituents of a mixture directly, if the peak areas are multiplied by a coefficient that depends upon the molecular masses of the solute and the carrier gas. The precision of such direct quantitative measurements is satisfactory, and every mixture thus analyzed can serve as a standard, either for determining the coefficients of response for any other detector, or for use with an automatic process chromatograph operating with a bar graph recorder. Since it avoids quantitative calibrations, the gas density balance is of certain importance in a control laboratory where rapidity of operation is of the utmost importance.

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