Powder blending homogeneity

S.S. Sekulic, H.W. Ward, D.R. Brannegan, et al. On-line monitoring of powder blend homogeneity by near-infrared spectroscopy. Anal. Chem., 68, 509 - 513 (1996). 

R.C. Lyon, D.S. Lester, E.N. Lewis, E. Lee, L.X. Yu, E.H. Jefferson and A. S., Hussain, Near-infrared spectral imaging for quality assurance of pharmaceutical products analysis of tablets to assess powder blend homogeneity, AAPS Pharm. Sci. Tech., 3(3), 1-15 (2002). 

Sekulic, S.S. Ward, H.W. Brannegan, D.R. Stanley, E.D. Evans, C.L. Sciavolino, S.T. Hailey, P.A. Aldridge, P.K., On-Line Monitoring of Powder Blend Homogeneity by Near-Infrared Spectroscopy Anal. Chem. 1996, 68, 509-513. 

Lyon, R.C. Lester, D.S. Lewis, E.N. Lee, E. Yu, L.X. Jefferson, E.H. 8t Hussain, A.S., Near-Infrared Spectral Imaging for Quality Assurance of Pharmaceutical Products Analysis of Tablets to Assess Powder Blend Homogeneity AAPS PharmSciTech. 2002, 3(3), article 17, 1-15. 

Lai, C.-K. Holt, D. Leung, J.C. etal., Real time and noninvasive monitoring of dry powder blend homogeneity AIChE J. 2001, 47, 2618-2622. 

Powder blend homogeneity macro and micro considerations... 

As felt above, the concept of powder blend homogeneity cannot be dissociated from the scale at which a mixture is observed. For continuous mixers, homogeneity must be defined at the level of the blend flowing out of the vessel, and falling down to a conveyor or any other transportation equipment. In the case of a batch mixer, the mixture structure can be particularly complex to define, but in practice and when the mixer is emptied, the content of the vessel is discharged through a pipe to a container or a tableting machine. Hence, in both cases and if we take into account the entire cross-section of the pipe, the mixture flow can be assimilated as a 1-D particle stream. 

Drennen, in his thesis defense, first used NIR to study homogeneity during processing of semisolid dosage forms [26]. The translucent state of the samples was addressed in the paper. Later he used similar approaches for the study of powder blend homogeneity. 

Sekulic et al. reported the online monitoring of powder blend homogeneity by NIR spectroscopy in 1996 [9]. The authors commented on the error associated with insertion of a sample thief into a powder bed due to distortion of a powder bed, adhesion of certain components to the thief with subsequent displacement, and preferential flow of some components into the thief, all factors that make the NIR method attractive and which are discussed more thoroughly elsewhere. For these reasons and others, the authors developed a method of monitoring the blending process that eliminates the need for withdrawing samples from a blender. 

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