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:

NIFDC (National Institutes for Food and Drug Control)

The release of new batches does not require the immediate discontinuation of old batches. Old batches shall be used within the validity period specified in the Updated Supply Information of National Pharmaceutical Reference Standards. For multiple announcements of the same item, the latest one shall prevail. If a discontinuation notice is issued during the validity period, the discontinuation information shall take precedence. Expired or outdated batches not listed in the latest announcement shall have their applicability verified independently. It is recommended to purchase and use reference standards on an as-needed basis.

USP (United States Pharmacopeia)

Except for Prednisone Tablets Reference Standard, new batches are not assigned an expiry date; batches marked as "current lots" are valid. Old batches are granted a service life of 3 to 12 months, and USP does not endorse the use of expired batches.

EDQM (European Directorate for the Quality of Medicines & HealthCare)

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.)