According to ICH 3.2.S.3.2, Primary Reference Standards (PRS) and Secondary Reference Standards (SRS) are defined as follows:

PRS are purchased from pharmacopoeia sources.  SRS are prepared according to the following ICH guidelines:

Characterization (UV, IR, 1H NMR, 13C NMR, MS), ICH M4Q 3.2.S.3.5 and 3.2.S.3.2.

Purity and Assay (HPLC):  ICH Q7A 1.1, 12.8 and Q6A, 2.11, 3.2, and 3.3

Specification (UV, IR, HPLC):  ICH: M4Q, 3.2.S.4.5