The effect of beam size on real-time determination of powder blend homogeneity by an online near infrared sensor.

Online blend uniformity study was conducted with a near infrared (NIR) sensor and a simulated formulation consisting of acetaminophen and four excipients. Quantitative calibration models were developed and validated for the sensor and assay results were obtained in real time for acetaminophen and three excipients. Mechanical thief samples were also collected during the study. The samples were analyzed offline by a bench-top near infrared spectrometer and used as reference. Comparison of the online and offline data shows a significant difference in standard deviation for acetaminophen and excipients. R.S.D. data calculated from the real-time assay values for acetaminophen was 3.5-13.2-fold lower than those from the offline results. The cause for the discrepancy is believed to be the large beam size of the online sensor. A simple complete-random-mixture model was used to explain the discrepancy. It is concluded that beam size is an important factor in quantitative online blending uniformity studies.