Automatic determination of aluminum and magnesium in antacid tablets by potentiometric titration has proved a boon to Pfizer
The determination of aluminum hydroxide and magnesium hydroxide in antacid tablets is traditionally carried out by manual complexometric titration using suitable colour indicators. According to the USP method, magnesium is titrated with Na2EDTA solution (Eriochrome black T as indicator).
For the aluminum determination an excess of Na2EDTA is added, then back-titration is performed with zinc sulphate solution (dithizone as indicator).
In the R and D laboratory of Pfizer Consumer Health Care in Caringbah an alternative determination method has been developed for antacids that allows mixtures of aluminum and magnesium ions to be analysed automatically by potentiometric titration.
A Metrohm titrator is used in combination with a sample changer.
After addition of 1,2-diaminocyclohexanetetraacetic acid (DCTA) and complex formation, the DCTA excess is titrated back with copper(II) sulphate solution using the ion-selective copper electrode as indicator electrode.
First the aluminum is determined under acidic conditions followed by the determination of magnesium under alkaline conditions.
The newly developed titration method for the automatic determination of aluminum and magnesium in antacid tablets is superior to the traditional manual USP method in many respects.
Decisive advantages are the increased reliability, the improved precision of the results as well as the saving in time and the associated higher sample throughput.
As - apart from sample preparation - the analyses are carried out fully automatically, laboratory personnel are freed from routine work thus saving time for other activities.
The automated titration system therefore is the system of choice whenever large numbers of tablets - eg from stability studies - need to be analysed.
