The materials to be sampled may belong to the following classes:
(a) Bulk materials, represented by:
(i) starting materials (including both drug substances and pharmaceutical aids) in solid, liquid, or semi-solid state;
(ii) vegetable drugs, such as leaves, herbs, flowers, seeds, fruits, roots, rhizomes and bark, in whole or broken state.
Special care may be needed for certain bulk materials, for example, for those that are very potent, toxic, hygroscopic, or light-sensitive, or require special microbiological precautions.
(b) Intermediates in the manufacturing process.
(c) Drug products (in-process as well as before and after packaging). For finished drug products the sampling procedure must take account of the official and nonofficial tests required for the individual dosage form (for example, tablets, parenteral preparations).
(d) Containers, packaging materials, and labels.
The sampling procedure must take account of the homogeneity and uniformity of the material.
(a) Homogeneity. A material is regarded as homogeneous when it is all of the same origin (for example, from the same batch) and as nonhomogeneous when it is of differing origins.
(b) Uniformity. A starting material may be considered uniform when samples drawn from different layers do not show significant differences in the quality-control tests. The following materials may be considered uniform unless there are signs to the contrary: organic and inorganic chemicals, purified natural products, various processed natural products like fatty oils and essential oils, plant extracts. The assumption of uniformity is strengthened by homogeneity, i.e. when the consignment is derived from a single batch.
Signs of nonuniformity include differences in shape, size or colour of particles in crystalline, granular or powdered solid substances, moist crusts on hygroscopic substances, deposits of solid material in liquid or semi-liquid products, and stratification of liquid products. Such changes, some of which may be readily reversible, can occur during prolonged storage or exposure to extreme temperatures during transportation.
Dosage forms may be considered uniform when different samples from the same batch comply with the relevant tests for uniformity.
Finally the sampling procedure must take account of the past experience with the material and with the supplier, and of the number of sampling units in the consignment.