Classification of the Reference Standards

Reference Standards

Reference standards (RS) (reference materials, reference standards, reference substances) — individual substances, which are used for quality testing and quality control, for comparison with the tested medicinal products when such products are assayed by physical-chemical and biological methods, if such assays are stipulated by appropriate quality specification (for example, by Pharmacopoeial monograph). RS are conventionally divided into biological and chemical RS. The same reference standard can be used both for physical-chemical and for biological analysis in accordance with instructions in Pharmacopoeial monograph (or other normative document. State reference standards the use of which is stipulated in the Russian Federation are described in National Pharmacopoeia of RF (section General Analytical Methods).

State Reference Standard

State Reference Standard (SRS) — is the reference standard with the quality parameters regulated in Pharmacopoeial monograph, which has been approved according to established procedure. For the analysis of the final medicinal products Working Reference Standards (WRS) of the drug substances (substances) can be used. WRS is the sample of the serial substance satisfying the requirements of corresponding quality standard of the medicinal product. (See Order of RF Ministry of Health of 01.11.2001 N 388 “On State Quality Standards of the Medicinal Products” (together with “OST 91500.05.001-00. Industry Standard. Quality Standards of the Medicinal Products. General Provisions”)).

Working Reference Standards

Working Reference Standards (WRS) are calibrated by comparison with State Reference Standards using the simplified procedure. In the event of reference standard consumption in large amounts, such RS are used instead SRS with a view of economy and also for convenience (to reduce the terms of delivery of SRS from the centralized sources). Therefore it is sufficient to obtain once the SRS of the substance and subsequently use WRS of the same substance for analytical purposes. In the Russian Federation the use of SRS is additionally complicated due to imperfection of existing National Pharmacopoeia. This imperfection arises from limited amount of Pharmacopoeial monographs on SRS of the substances of plant origin and their absence in RF NF.

Furthermore, the most State Reference Standards specified in respective Pharmacopoeial monographs at present are either unavailable for acquisition, or are produced in insufficient amounts.

In accordance with international classification the reference standards of the substances are categorized into primary standards (Primary) and secondary standards (Secondary).

Primary Standards

Primary standards — are the top grade reference standards, with their purity characterized by several analytical methods, and test results are officially documented. Primary standards should be accompanied by comprehensive Certificate of the Analysis, specifying chromatographic purity (based on HPLC), water content (according to Karl Fischer method), residual solvents (based o GLC), results of structure identification (by mass-spectrometry and NMR-spectroscopy).

Primary standards are intended for the following purposes:
  • to test reproducibility in the series of high-accuracy quantitative measurements;
  • to attest/validate analytical methods or procedures of measurements (POM);
  • to verify/calibrate measuring equipment;
  • within the programs of analytical laboratory testing for competence;
  • to develop analytical methods or procedures of measurements.

Secondary Standards

Secondary standards (SH, SG, ST) — are the reference standards of lower grade compared with primary standards. The purity of secondary standards should be characterized by HPLC, GLC or TLC, respectively. Secondary standards have been investigated and characterized not so comprehensively as primary standard.

The main areas of application:
  • at the initial stage of development of analytical method or procedures of measurements;
  • for stability study of the compound (pure substance);
  • in vitro or in vivo studies;
  • for quality control;
  • for identification of the analyte;
  • as a working reference standards (WRS) or in-house reference standard (IRS).