Bulk density and tapped density of powders

Headnote

The International Pharmacopoeia

(ProQuest: ... denotes formulae omitted.)

Draft proposal for inclusion of a General Method in the 4th Edition of the International Pharmacopoeia (September 2011). Please addess any comments to Quality Assurance and Safety: Medicines, World Health Organization, 1211 Geneva 27, Switzerland. Fax: [phone] or e-mail [email protected]. All working documents are available for comment at http://www.who.int/medicines/publications/pharmacopoeia/mono_dev/en/ index.html

[Note from the Secretariat: This new general method text is proposed for inclusion in the Supplementary information section of The International Pharmacopoeia (Ph. Int.). The text is based on the internationally harmonized test on bulk density and tapped density of powders.

It is intended to revise the Supplementary Information section of the Ph. Int. (structure and contents). In the proposal currently being reviewed, a new section on Test Methods used during pharmaceutical development and/or manufacture of dosage forms is included. The general method for bulk and tapped density of powders would, therefore, be included in this section and a specific number will be assigned to this method once the proposed format and the methods considered for this section are adopted.]

Bulk density

The bulk density of a powder is the ratio of the mass of an untapped powder sample and its volume including the contribution of the interparticulate void volume. Hence, the bulk density depends on both the density of powder particles and the spatial arrangement of particles in the powder bed. The bulk density is expressed in grams per millilitre (g/ml) although the international unit is kilogram per cubic metre (1 g/ml - 1000 kg/m3) because the measurements are made using cylinders.

It may also be expressed in grams per cubic centimetre (g/cm3).

The bulking properties of a powder are dependent upon the preparation, treatment and storage of the sample, i.e., how it was handled. The particles can be packed to have a range of bulk densities and, moreover, the slightest disturbance of the powder bed may result in a changed bulk density. Thus, the bulk density of a powder is often very difficult to measure with good reproducibility and, in reporting the results, it is essential to specify how the determination was made.

The bulk density of a powder is determined by measuring the volume of a known mass of powder...