Chem. Pharm. Bull. 54(3) 384—386 (2006)

superior speed and simplicity with little sacrifice in accuracy and precision. Phenytoin sodium (DPH) forms phenytoin silver collosol quantitatively with silver nitrate solution. The reaction between phenytoin sodium and silver nitrate reveals a 1 : 1 molar ratio as illustrated in Chart 1. However, there was no accurate method available to determine the titration end-point. Therefore, gravimetric, potentiometric titration, high-performance liquid chromatography (HPLC), and other complicated methods are often used. The instrumental method is generally not as accurate and precise as the titrimetry in macro analysis. Besides, gravimetric is now rarely used in the laboratory for its inconvenience. Our previous study revealed a possibility of using highly accurate nephelometric titrimetry to determine phenytoin sodium. Now, as a continuous study, this accurate, rapid and simple titration method was developed for the quantitation of phenytoin sodium injection and tablets. An internal nephelometric sensor was immersed in the titrate to monitor the change in the intensity of the scattered light during the titration. After adding the first drop of the silver nitrate solution, the phenytoin sodium solution became cloudy, and, as the titration continued, the scattered light detected increased gradually. As more titrant was added after passing the point, the solution would not become cloudier and the scattered light would not increase; on the contrary, the scattered light would decrease in intensity because of the dilution of the solution. A peak would appear at the stoichiometric point in the profile of relative intensity of scattered light versus the volume of titrant and therefore the end-point of the titration could be determined accurately. The titration operating conditions were optimized in the present study. The proposed method has been validated and found to be precise and accurate. The results acquired by highly accurate nephelometric titrimetry are comparable to those by the control experiments under the operating conditions.