A promising general method has been developed for the detection and continuous recording of component bands in chromatographic separations employing liquid eluents (paper, string or packed column chromatography).
Since the method is based primarily upon colligative, rather than structural, properties, its applicability is not limited to specific classes of components or eluents. ,, PRIh'CII'LES Fhc method utilizes measurements of the temperature differential which is established between a cellulose wick saturated with-the pure eluting solvent and a similar wick which is continuously bathed with the liquid effluent from the chromatographic column ; both wicks are enclosed in a thermostatted chamber saturated with solvent vapor. The use of thermistors as the temperature-sensing elements permits use 0% 'a' conventional Wheatstone bridge circuit, which can bc balancecl when both wicks arc bathed with pure solvent. Since a small electrical ck-rent passes continuously through the thermistors in the bridge circuit, the temperatures sensecl by the thern$stors depend primarily upon competition. between the following processes of heat input and heat removal.
I. Heat input : a. Electrical heating of the thermistor. b. Heat evolved by condensation of solvent on the wick.
- Heat removal: a. Thermal conduction of heat. to the liquicl flowing through the wick. b. Heat absorbed in vaporization of the solvent (ancl, possibly, volatile solutes) from the wick.
The electrical heating and liquid flow are held essentially constant. When the column effluent liquid contains solute in a compdnent band, the thermal conductivity 7 of the eluting solvent is not significantly altered by the presence of solute. The vapor pressure of solvent, however, is lowered by the presence of solute, causing the ratio of the rate of vaporization to the rate oi condensation to become lower on the sample