Lactose is 4-O-β-D-Galactopyranosyl-α-D-glucopyranose monohydrate. It contains not less than 98.0% and not more than 102.0% of C12H22O11, calculated on the anhydrous base. The monograph specifies lactose in terms of the following aspects:

- description;

- specific optical rotation;

- identification;

- acidity;

- clarity and color of solution;

- related substances;

- protein and absorbance of impurity;

- loss on drying;

- water;

- residue on ignition;

- heavy metals;

- arsenic;

- microbial limit;

- assay

- chromatography conditions and system suitability test;

- category;

- storage.