Measurement of Solution Composition as an Alternative to Titration for Evaluating the Hydrolytic Resistance of Glass

The measurement of solution composition is proposed as an alternative to titration to determine titration volume, which is the figure of merit for evaluating the hydrolytic resistance of glass containers for pharmaceutical packaging. In the new method, instead of titrating the sample and blank solutions, their compositions are measured by inductively coupled plasma mass spectrometry, and these compositions are converted to titration volume using a set of coefficients and a simple equation. The coefficients were derived using the well-developed thermodynamic data and models for dilute aqueous solutions, which make it possible to calculate the pH from the solution composition and then simulate a titration as a series of pH calculations as titrant is progressively added to the solution. In this article, we explain how a titration can be simulated, describe how the set of coefficients was derived, and provide experimental evidence that the titration volume from the new method is equivalent to that from titration. Since the new method is more difficult and expensive, it is not meant as a replacement for titration in the standard and pharmacopeial methods. Its value lies in enabling previously impossible hydrolytic resistance studies, supplying additional information about the composition of the hydrolytic solution that reveals important aspects of glass corrosion, and providing insights about titration that point to possible improvements in the standard titration procedures.