Particle-Size Characterization

Authored by: Brian H. Kaye

Encyclopedia of Pharmaceutical Science and Technology

Print publication date:  July  2013
Online publication date:  July  2013

Print ISBN: 9781841848198
eBook ISBN: 9781351124874
Adobe ISBN:


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The subject of powder sampling has been addressed extensively in standard reference books. Several companies sell sampling equipment for installation in industrial systems (17). Even when the sample received by the laboratory is a representative sample, the analyst still faces the difficult task of taking a small subsample from the powder supplied. It has been shown that one of the most efficient devices for taking a subsample of the powder is known as the spinning riffler, shown in Fig. 1A. It consists of a ring of containers that rotates under the powder supply. The total powder supply is processed using this instrument. It has been shown that to obtain a representative sample, the time of powder flow through the apparatus divided by the time of rotation of the ring of containers should be a large number (4,7). Difficulties arise using such devices with very fine powders because air currents caused by the rotation of the system can blow the fines away. Furthermore, if the powder is cohesive (sticky), thepowder flow through the funnel can be impeded. In some situations, the flow properties of the powder can be modified by addinga silica flow agent, provided this does not interfere with the size characterization procedures used subsequent to the sampling procedure (8).

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