Determination of the content of active ingredients in traditional Chinese medicine (1)

The content determination of traditional Chinese medicine is an important indicator in quality control.

Traditional Chinese medicine preparations are mostly composed of compound prescriptions.

There are many methods for quantitative analysis of traditional Chinese medicine preparations, including electrochemical methods, chemical analysis methods, biochemical methods, etc.

1.

If the Chinese herbal medicine contains more than one alkaloid, the measured content is the total alkaloid content, which is an approximate value calculated based on the main alkaloid

There are many methods for determining the content of alkaloids, and the volumetric method is the most widely used

When determining the content of alkaloids in medicinal materials or preparations, the sample must first be extracted, purified and separated to eliminate the interference of impurities and quantitatively determine the content of alkaloids

The extraction and purification of alkaloids is carried out according to the differences in the solubility of alkaloid salts and free alkaloids in water and in water-immiscible organic solvents

(1) Volume method

Volumetric analysis is a method of calculating the content of the measured component based on a reagent solution of a known concentration (standard solution) and the volume consumed when the measured component is fully reacted.

1.

(1) Reaction principle: Alkaloids are nitrogen-containing organic compounds that are alkaline.

The essence of the reaction in the titration process can be expressed by the following simple formula:

Standard solutions can be used to titrate alkaline substances, and standard solutions can also be used to titrate acidic substances

(2) The calculation formula of titration analysis: If the volume of the solution of the substance to be tested is VA and the concentration is CA, the volume of the titrant with the concentration of Cr used when it reaches the stoichiometric point is Vr

In titration analysis, the volume is often calculated in ml

Formula (14-9) and Formula (14-10) are the most basic formulas for titration analysis and calculation, and their application should be discussed in conjunction with specific examples

(3) Requirements for chemical reactions used in titration analysis:

1) The reaction must be completed quantitatively

2) Respond quickly
.
The titration reaction is required to be completed in an instant.
For slower reactions, appropriate measures should be taken to increase the reaction speed
.

3) There must be a simple and reliable method to determine the end point
.
Such as indicator method or other physical and chemical methods
.

(4) Matters needing attention

1) If the alkaloids are extracted with organic solvents after alkalization with ammonia, the ammonia should be removed to prevent the alkaline substances from interfering with the measurement results
.
Generally, after the organic solvent is evaporated to dryness, a small amount of chloroform or ethanol is added , and then evaporated to dryness to remove excess ammonia
.

2) If chloroform is used as the solvent to extract the alkaloids, be careful when evaporating to dryness that the chloroform will decompose to form hydrochloric acid when heated for a long time, which can combine with the alkaloids to form a salt, resulting in low titration results
.
In order to avoid its decomposition, when heating, add a small amount of ethanol and then steam when the chloroform is evaporated to nearly dryness , so as to drive off the chloroform first and then evaporate to dryness
.

3) Choose a suitable indicator
.
The selected indicator should change its color at the equivalence point of the alkaloid to be titrated to indicate the end point
.

2.
Extraction method

(1) Reaction principle: Liquid-liquid extraction method is also called solvent extraction method, which uses the difference in the distribution coefficients of the components in the mixture in two immiscible solvents to transfer the substance to be tested from one liquid phase to another.
Phase and the method to achieve the purpose of separation
.

Suitable solvents can be used to directly extract impurities to separate the predicted components.
For example, petroleum ether can be used to remove fatty oils and lipophilic pigments.
The properties of the predicted component solubility can also be used to make it dissolve in lipophilic solvents and hydrophilic after repeated treatment.
In order to remove water-soluble impurities or fat-soluble impurities
.

(2) Matters needing attention

1) When the extraction is easy to emulsify, avoid violent shaking to extend the extraction time
.
If emulsification occurs, it can be placed for a long time and rotated from time to time to allow it to separate naturally; or separate the emulsified layer and extract with a new solvent
.

2) The ratio of solvent to aqueous solution should be kept in a certain amount.
Generally, the amount of solvent for the first time should be 1/3 of that of the aqueous solution, and the amount afterwards is generally 1/6 to 1/4
.

Related Links: Assay methods included in the general rules of the Chinese Pharmacopoeia (4)