Development of a thermogravitational microcolumn with an interferometric contactless detection system.

We present a new type of thermogravitational (TG) column, a so-called TG microcolumn with transparent windows and a very small sample volume of less than 50 μL. The TG microcolumn has a planar geometry with a thickness of 0.523 ± 0.004 mm, a height of 30 mm, and a width of 3 mm. The concentration difference between two points at different heights is measured with an interferometer using active phase control. From the concentration difference we can determine the thermal diffusion coefficient, D(T), using the refractive index variation with concentration, which has to be determined independently. We studied the three binary mixtures of dodecane, isobutylbenzene, and 1,2,3,4-tetrahydronaphthalene with a concentration of 50 wt % at a temperature of 298 K. The thermal diffusion coefficients agree within a few percent with the proposed benchmark values. In addition we investigated also the binary mixture toluene/n-hexane and compare the results with literature values. For the investigated mixtures the typical measurement times were between 30 min and 2 h with an applied temperature difference of ΔT = 6 K.