Surface characterization of 2-hydroxypyrimidine sulphate by inverse gas chromatography

Abstract

The net retention volumes, V _N , of n-alkanes and polar probes on 2-hydroxypyrimidine sulphate (2-HPS) drug surface are determined at 323.15, 328.15 and 333.15 K using inverse gas chromatography. The dispersive surface free energy, $\gamma_{S}^{d}$ of 2-HPS are evaluated by applying Schultz method as well as Dorris–Gray method and found that $\gamma_{S}^{d}$ values are higher by 8 per cent in the latter method. The $\gamma_{S}^{d}$ values are decreasing in both the methods with increase of temperature. The specific component of the free energy of adsorption, $\Updelta G_{a}^{S}$, for polar probes are obtained by three methods proposed by Schultz et al., Saint Flour–Papirer and Sawyer–Brookman. The Lewis acid–base parameters, K _a and K _b , are calculated using $\Updelta G_{a}^{S}$ values. The surface character value, S = (K _b /K _a ) according to the Schultz et al., is found to be 3.9 whereas the S value in the other two methods are found to be 6.2 and 5.6. The results demonstrate that the 2-HPS powder surface contain relatively more basic sites and can interact strongly in the acidic media.