① Regarding the stability of the standard substance (reference substance):

Q: Due to the large packaging specifications of the reference material, it needs to be used multiple times before it can be used up. How to ensure the stability of the product?

Answer: The stability of reference materials generally comes from reference materials recognized by regulatory authorities. As long as they can be stored under the recommended storage conditions by the provider, there is no need to conduct further stability studies. For reference materials from other sources, stability studies should be considered, including the stability of solutions prepared for the use of reference materials in quality standards. Based on the stability research results and other research data, confirm the packaging, storage conditions, and retest period (validity period) of the reference substance; Clarify whether necessary treatments have been carried out on the packaging, such as nitrogen filling, sealing, etc; Explain the special operations carried out when using the reference substance, such as whether drying treatment is required and processing conditions, and whether it can be used multiple times.

② Change of new and old batches of standard (reference):

Q: How can pharmacopoeia standards be used within their expiration date?

Answer: Most countries do not set an expiration date for drug standard substances, but continuously monitor the quality stability of currently effective batches on sale. Once it is found that the quantity value is not applicable, a suspension notice will be issued immediately. If the official has not issued a notice of discontinuation or announced the effective period of use for the previous batch of standard substances in a certain variety's current sales batch, they should be stored according to the conditions specified in the instruction manual. Generally, the China Inspection Institute can use them normally within 6 months; EP can refer to the EP online standard product database; USP usually takes 3 to 12 months after the current batch is sold out.

For statutory standard products, it is recommended that users purchase them as needed or according to production and inspection plans. Do not hoard large quantities in advance, because once new batch numbers start to be supplied externally, quality monitoring of old batch numbers will no longer be carried out. If users continue to use them, their characteristic values and suitability should be verified by themselves.

③ Regarding the weighing method for oily substances:

Q: How to weigh oily substances?

Answer: There are two common methods:

1. Direct weighing

Instrument: A clean spoon, a clean sample bottle, an analytical balance, and clean powder free gloves.

Step:

(1) Weigh the weight of the sample bottle.

(2) Dip the sample with a spoon, take a small amount multiple times, and put the dipped sample into an empty bottle until you obtain the desired quality.

2. Sampling after dissolution

Dissolve the sample in a quantitative solvent and prepare a solution of a certain concentration. Then calculate the volume of the required sample and take a sample for testing. (Due to the particularity of the sample, it is not recommended to dissolve it in the solvent for a long time. It needs to be used up in a timely manner. Prolonged dissolution of the sample in the solvent may cause degradation.)