INTRODUCTION

Refractive index is a basic physical property of pharmaceutical materials. This general chapter only applies to the measurement of liquid pharmaceuticals, solutions, solvents, and liquid raw materials with stand-alone instruments and not to detectors of chromatographic systems. Refractive index measurements of liquid pharmaceuticals, solutions, solvents, and liquid raw materials are useful for the following:

• Identifying a pure substance

• Establishing the purity of some substances

• Determining the concentrations of some solutions such as alcohol solutions or sugar solutions (e.g., percentage of sugar in syrup)

• Determining the uniformity of final compounded preparations

The refractive index (n) of a substance, or medium, is defined as: n = c v