Rapid assessment of sedimentation stability in dispersions using near infrared transmission measurements during centrifugation and oscillatory rheology.
We used the LUMiFuge) 114 particle separation analyser to investigate the sedimentation kinetics of bentonite/xanthan gum mixtures through pH 2-7 during centrifugation. This new technique monitors timed near infrared transmission profiles of different samples in the centrifugal field. Statistical analysis of the data then identifies the formulations with minimal clarification tendency. All mixtures were characterised by rotational and oscillatory rheology. Various rheological parameters correlated with the LUMiFuge clarification data, most notably the relaxation exponent, n and loss tangent, tan delta. We devised a combined desirability function for the different mixtures, defining maximal desirability as the minimal values for the two oscillatory parameters. The results matched those of separation analysis in the centrifugal field.We conclude that the experimental design is suitable for selecting formulations with optimal sedimentation stability whether combined with LUMiFuge analysis or oscillatory measurements. The method can be used to screen formulations for optimal long-term stability test performance, with significant potential savings and minimal sedimentation risk after prolonged storage.
Kuentz
Martin
M
F. Hoffmann-La Roche Ltd., Basel, Switzerland. martin.kuentz@roche.com
Röthlisberger
Dieter
D
D002498:Centrifugation / Q000379:methods; D004364:Pharmaceutical Preparations / Q000032:analysis / Q000737:chemistry*; D012212:Rheology; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D014783:Viscosity
D004364:Pharmaceutical Preparations