Purity is closely linked with the safe use of drugs and deals with factors such ash values, contaminants (e.g. foreign matter in the form of other herbs), and heavy metals.
Modern purity evaluation also includes microbial contamination, aflatoxins, radioactivity, and pesticide residues.
Analytical methods such as photometric analysis, thin layer chromatography (TLC), high performance liquid chromatography (HPLC), and gas chromatography (GC) can be used in order to establish the constant composition of herbal preparations.