Determination of Ephedrine Hydrochloride in Mixtures of Ephedrine Hydrochloride and Pseudoephedrine Hydrochloride Using near Infrared Spectroscopy

There are a number of situations where there is a need to determine the concentrations of components in solid-state mixtures without dissolving the samples. The experiments described here were designed to demonstrate that diffuse reflectance near infrared spectroscopy coupled with partial least squares (PLS) data analysis can be used to determine the minor component in a mixture of structurally-similar solid-state compounds, in this case mixtures of ephedrine hydrochloride and pseudoephedrine hydrochloride. It is shown that when care is taken to produce homogeneous calibration samples very good results can be obtained; in this case, cross-validated standard error of predictions of 2.30 wt% when the minor component spanned the concentration range of 0 to 50 wt% and 0.30 wt% when the minor component spanned the concentration range of 0 to 5 wt%. Results are presented that indicate that the amount of data available to the PLS calibration routine relative to the range over which the calibration is performed can limit the precision and accuracy of the determinations.