ABSTRACT
<p><b>AIM</b>To indicate the titration end-point of precipitation reaction by measuring the relative intensity of the scattered light in the titrate for use in pharmaceutical analysis.</p><p><b>METHODS</b>A visible light-emitting diode (LED) was used as a light source and a photodiode was used as the optical detector. Light on the detector creates an electric current through the diode. With the addition of the titrant, the titrate became turbid and the intensity of the scattered light in the solution increased gradually. If the precipitation reaction proceeded the completion and the solubility of the precipitate was small enough, the intensity of the scattered light will reach maximum at the stoichiometric point; thus, the titration end-point can be indicated. The accuracy of nephelometric titrimetry was discussed theoretically and the titration of NaCl with AgNO3 was used as a model. To demonstrate the applicability of the new titrimetry in pharmaceutical analysis, phenytoin sodium and procaine hydrochloride were titrated with AgNO3 and NaOH solutions, respectively.</p><p><b>RESULTS</b>With our new titrator and nephelometric sensor, the accuracy and precision of our new titrimetry can be better than 0.2% under suitable conditions.</p><p><b>CONCLUSION</b>This new titrimetry can be used for pharmaceutical analysis.</p>