Optimization of the Thin-Layer Chromatography Method for the Separation of Ziprasidone and Its Impurities

Abstract

The experimental design and the quantitative structure-retention relationship (QSRR) study were applied in order to investigate the retention behavior and to select optimal experimental conditions for the separation of ziprasidone and its five impurities by thin-layer chromatography (TLC). According to a preliminary study, central composite face-centered design was chosen to examine the influence of four factors, i.e., the developing distance, the amount of toluene in the mobile phase, the amount of acetic acid in the mobile phase, and the spot band size, on the retention behavior of the examined compounds. The optimal separation conditions were achieved on the chromatographic plates precoated with silica gel 60 F-254 using toluene-methanol-glacial acetic acid (7.5:0.5:0.5, v/v) as the mobile phase in combination with a band width of 6 mm and a developing distance of 110 mm. The retention parameters (hR(f)) obtained under the selected chromatographic conditions, along with the calculated molecular descriptors, were further used for the QSRR study. Statistically, the best QSRR model (R-2: 0.939, Q(2): 0.916, and RMSEE: 2.98) composed of the three significant variables, i.e., the harmonic oscillator model of aromaticity (HOMA) index, the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) energy, was developed, using the partial least square methodology. A very good agreement was obtained between the QSRR predicted and the experimentally observed hR(f) values for an additional ziprasidone impurity (TS1). These results point out to a high prediction potential of the developed QSRR model for the evaluation of the retention behavior of the other ziprasidone impurities.