A rapid determination of allantoin by high-performance liquid chromatography using tris(hydroxymethyl)aminomethane-HCl buffer as a mobile phase

A rapid and simple method for the determination of allantoin in pharmaceuticals by reversed-phase ion-pair high-performance liquid chromatography using an ODS column was presented. In general, it is difficult to retain allantoin to the ODS column owing to its very low hydrophobicity. We solved these problems by the use of a Tris-HCl buffer (pH 7.5) containing tetra-n-hexyl-ammonium bromide (THAB) as an ion-pair reagent for the mobile phase. Comparatively low concentrations of Tris-HCl buffer (0.9 mM) and THAB (0.5 mM) gave a high capacity factor (k'). As a results of the examination of the chromatographic behavior, it is confirmed that the retention mechanism of allantoin to the ODS column on the present method was not the ion-pair mode, but the ion-exchange mode. Calibration curves for allantoin showed a good linearity in the range of 10 to 400 micrograms/ml (r = 0.9999). The reproducibility (R.S.D., n = 6) was invariably good (0.37%). The lowest concentration of allantoin for the determination was 200 ng per 20 microliters of injection. The present method was successfully applied to the determination of allantoin in commercial eyedrops with good recovery (99.4%). It was found that allantoin in pharmaceuticals could be determined by the present method in short time and without any complicated derivatization.