Both active and inactive (excipient) compounds are used in the manufacture of solid dosage formulations, i.e. tablets and capsules. These powders possess many properties or characteristics and exhibit certain behaviors as a result.
One important characteristic is tapped bulk density, or simply tapped (tap) density: that is, the maximum packing density of a powder (or blend of powders) achieved under the influence of well defined, externally applied forces. The minimum packed volume thus achieved depends on a number of factors including particle size distribution, true density, particle shape and cohesiveness due to surface forces including moisture. Therefore, the tap density of a material can be used to predict both its flow properties and its compressibility. These are just two of the many parameters which are important in the overall tabletting process - which requires that loose powders be compacted into a durable solid form with the correct mechanical strength, porosity and dissolution characteristics – and in capsule filling performance.
Compressibility Index & Hausner Ratio
The two most commonly used measures of the relative importance of interparticulate interactions are the compressibility index (often referred to as Carr’s Index) and the Hausner ratio. “V” and “D” represent powder volume and density respectively, subscript “o” denotes the initial or untapped state and “f” the final or tapped state. In free-flowing powders the initial bulk and tapped densities will be more similar than in poor flowing powders which yield greater differences between the two values.
Figure 1. Carrs Index and the Hausner Ratio
Autotap & Dual Autotap
The Autotap and two-sample Dual Autotap conform to USP 616 , for Tapped Density (Method II).
The measuring cylinder containing the powder sample is dropped a height of 3mm (1/8”) at a rate of approximately 250 drops per minute. Both Autotaps feature a drop counter which can be set to any value from 1 to 9999. An optional lock-out mechanism is available to prevent tampering with a preset number of counts. Quantachrome’s Autotaps therefore can contribute a vital role in the development and assurance of solid dosage formulations in the pharmaceutical industry.