Drug control laboratories are less frequently involved in the sampling of pharmaceutical starting materials, although they may be called upon to assess the quality of imported consignments. Again, this assessment must be undertaken using samples collected in accordance with an appropriate procedure, because a poorly collected sample may provide misleading information. The sampling procedure must have regard to whether or not the material can reasonably be considered as uniform. A more complex procedure must be employed when there is a suspicion of nonuniformity.
If the material of a consignment can be regarded as uniform, the sample can be taken from any part of the consignment. If, however, the material is not physically uniform, special sampling tools may be required to withdraw a cross-sectional portion of the material. In some instances, however, an attempt can be made to restore the uniformity of the material before sampling. Thus, a stratified liquid may be stirred, or a solid deposit in a liquid may be dissolved by gentle warming and stirring. Such interventions are difficult when the containers are large and they should not be attempted without adequate knowledge of the properties of the contents.
All partially processed natural products both herbal (dried plants and their parts) and mineral, should be treated as intrinsically nonuniform. Special procedures requiring considerable practice are used to prepare representative samples from such consignments, including coning and quartering and the treatment of fines. These procedures are not further described in these guidelines.1
1 Sampling procedures for crude natural products are given in several sources, such as: General control methods for vegetable drugs. Unpublished WHO document WHO/PHARM/80.502; The United States Pharmacopeia XXI, seventh supplement. Rockville, MD, The United States Pharmacopeial Convention Inc., 1988, p. 2859; [State Pharmacopoeia of the Union of Soviet Socialist Republics], eleventh edition. Moscow, Medicina, 1987, pp. 267-274.