SAMPLING PRACTICES IN POWDER BLENDING

Blending and sampling of granular materials are discussed in the conte xt of pharmaceutical operations. Several experiments are used to compa re the state of the art with regulatory expectations, especially those highlighted in a recent court ruling generally known as the 'Barr Dec ision'. It is shown that samples obtained using thief probes can exhib it considerable errors, possibly leading to misleading results. The ef fects of sample size and number of samples are examined using an alter native characterization technique in which a powder mixture is solidif ied through infiltration with a polymer solution, sliced, and examined using image analysis. It is shown that number of samples is the most important parameter controlling the accuracy of the characterization. While a homogeneous mixture can be accurately characterized using just 30 samples, poorly mixed systems require hundreds of samples. It is a lso shown that an accurate characterization of a mixture inside a blen der may nor be indicative of the final state of the mixture after addi tional processing steps. (C) 1997 Elsevier Science B.V.