Specific Interactions

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In addition to the Dispersive parts of the surface energy, you can measure the Specific, more polar, characteristics.

Specific Interactions

Tmeasure °C

A set of IGC measurements with alkane probes gives their Vg values (specific retention volumes) which in turn are normalised values calculated from retention times. From these Vg values the free energy of absorption, ΔG can be calculated via:

ΔG = RTmln(Vg)

where R is the universal gas constant, Tm is the measurement temperature (converted from °C to K).

In addition the Vg value of different polar probes are measured. Knowing the topology index χT of the polar probe and knowing the ΔG of the probe, the specific interaction parameter , ISP or ΔGSPa, is the difference between point of the polar probe ΔGa and the respective dispersive term ΔGda at the same molecular descriptor χT.


Note: herein, the molecular descriptor χT is calculated by taking considering the geometry of the polar probe molecules [Brendlé and Papirer (1997b)1]. This correlates well with the literature data concerning their polarizabilities [Balard et al. (2000a)2].

Enter Vg values for at least two alkanes along with the Vg for your probe molecule plus its χT selected from the following list of some of the polar probes taken from the Brendlé paper:

The data points and the least squares fit which defines the reference line and the theoretical value of VgLinear are shown.

1Eric Brendlé and Eugène Papirer, A New Topological Index for Molecular Probes Used in Inverse Gas Chromatography: 2. Application for the Evaluation of the Solid Surface Specific Interaction Potential, Journal of Colloid and Interface Science, 194, 217–224 (1997)
2Balard et al ref to be supplied

The IGC apps are based on the inputs kindly provided by Dr Eric Brendlé of Adscientis who are specialists in IGC measurements.