Strategies for constructing the calibration set in the determination of active principles in pharmaceuticals by near infrared diffuse reflectance spectrometry

The active principle in the blended phase of a commercially available pharmaceutical preparation was determined using near infrared diffuse reflectance spectrometry in combination with a fibre optic probe and multivariate calibration by partial least-squares regression. Two different ways of preparing laboratory samples spanning an appropriate concentration range for constructing the calibration set were compared. One of the procedures involves Preparing synthetic samples by weighing and the other using under-and overdosed production samples. Although the;results provided by the two strategies were not significantly different, the second was judged more effective because it has a less marked effect on those physical properties of the samples that affect the IR spectrum. The prediction errors obtained (less than 1%) indicate the suitability of the proposed sample preparation procedure, which is faster than the usual method of choice and provides comparable results.