According to relevant regulations, the sources of standard samples (reference samples) used for drug product inspection in China include: first, the standard samples (reference samples) provided by the China National Institute for the Control of Pharmaceutical and Biological Products; The second is the standards (reference standards) of other countries; The third is the standard substance (reference substance) calibrated by drug inspection institutes at or above the provincial level and approved by the same level food and drug regulatory bureau. However, during on-site inspections, we found that some pharmaceutical manufacturers use refined raw materials or "working standards (reference materials)" due to certain reasons. The "working standard (reference substance)" refers to the raw material used as a standard (reference substance) with a known content that has been calibrated in this laboratory. The working standard (reference standard) is required to be managed according to the standard (reference standard) and used for finished product inspection instead of the standard (reference standard).

The Standardization Committee tentatively defines a standard substance (reference material) as a substance whose one or more physical or chemical properties have been fully determined and used to calibrate instruments or confirm a measurement method, and divides it into three levels.

1. A first level standard substance (primary reference substance) is a stable and homogeneous substance that has been determined by deterministic methods or highly accurate methods, and its impurities have also been quantified. It can be used to calibrate deterministic methods, evaluate and calibrate reference methods, and to set values for "secondary standard products". All first-class standard products have certificates, which are issued by the National Bureau of Standards (NBS) in the United States with a certificate of conformity indicating their nature and relevant data.

2. Secondary standard samples (secondary standard samples) or pure solutions (solutions of water or organic solvents collected and organized by Medical Education Network), or exist in similar matrices. This type of standard can be prepared by the laboratory itself or as a commodity, and the amount of the relevant substance is determined by reference method calibration or comparison with primary standard. It is mainly used for standardization of conventional methods or calibration of control substances.

3. Control substances can be freeze-dried or in solution, and can be determined using appropriate standards (first or second grade) as reference methods for quality control, not for standardization (except for those determined by standards).