Extraction and separation of alkaloids

1. Water or acid water extraction method

(1) Alkaloids are in the form of salts in the plant body, and are often extracted with inorganic acid water. Make alkaloids of large molecules of organic acid salts into small molecules of inorganic acid salts, increase the solubility in water, and the method is relatively simple.

(2) commonly used 0.1% ~ l% of sulfuric acid, hydrochloric acid or acetic acid, tartaric acid solution as an extraction solvent, using impregnation or percolation method of extraction.

(3) The main disadvantage is that the volume of the extract is large, difficult to concentrate, and more water-soluble impurities. Therefore, after extraction with acidic water, the following methods of purification and enrichment of alkaloids can generally be used:

1) Cation resin exchange method

The alkaloid salts can be dissociated from alkaloid cations in water, which can be exchanged to the cation exchange resin by ion exchange reaction with the cation exchange resin. After the exchange is complete, the impurities in the column are washed out with neutral water or ethanol. Finally, the alkaloids are then eluted from the resin by an appropriate method (acidic water or acidic ethanol).

2) Extraction method

The acid-water extract is alkalized, and the alkaloids are free, such as precipitation, filtration is obtained; if not precipitated, extraction with appropriate lipophilic organic solvents, recovery of solvents, that is, the total alkaloids.

2. Alcohol solvent extraction method

(1) Free alkaloids or their salts are soluble in methanol, ethanol, alcohol reflux or percolation, impregnation and other methods of extraction.

(2) Advantages: wide adaptability, alkaloids and salts of different alkalinity can be used, extracted water-soluble impurities are less. Disadvantages: more fat-soluble impurities.

(3) It can also be treated with acid-water-alkalization-extraction method to remove fat-soluble impurities.

The specific method is to recover alcohol from the alcohol extract with dilute acid and water stirring, filtration, filtrate alkalization to lipophilic organic solvent extraction, recovery of solvents that is the total alkaloids.

3. Lipophilic organic solvent extraction method

(1) Most of the free alkaloids are lipophilic, so we can use chloroform, benzene, ether, etc. to extract free alkaloids. It can be extracted by maceration, reflux or continuous reflux method.

(2) However, the herbs should generally be extracted after wetting with a small amount of alkaline water in order to free the alkaloids and also to increase the penetration of the solvent into the plant cells.

(3) Volatile alkaloids such as ephedrine can be extracted by water vapor distillation. Sublimatable alkaloids such as caffeine can be extracted by sublimation.

The separation of alkaloids:

1. Separation using alkalinity difference

(1) The alkalinity of each alkaloid in the total alkaloid is different, and it can be separated by pH gradient extraction.

(2) the total alkaloids dissolved in chloroform and other lipophilic organic solvents, with different acidic buffer according to the pH from high to low sequential extraction, alkaloids can be separated according to the alkalinity of the strongest to the weakest successively into the salt is extracted, respectively, alkalization can be extracted with organic solvents.

(3)Dissolve the total alkaloids in acidic water, gradually add alkali to make the pH value from low to high, every time the pH value is adjusted, i.e., chloroform and other organic solvents are used to extract, the monomer alkaloids according to the alkalinity of the weakest to the strongest successively into the salt is extracted in turn and separated.

2. Use of solubility differences for separation

(1) free alkaloids: such as ginseng in the ginseng ginseng and the separation of ginseng oxide ginseng alkaloids, can be used to oxidize ginseng alkaloids polarity is difficult to dissolve in ether, ginseng alkaloids can be soluble in ether, the ginseng ginseng total alkaloids dissolved in chloroform, and then add more than 10 times the amount of ether, the oxidized ginseng alkaloids can be precipitated. The polarity of the ethanol in Hansenula officinalis is greater than that of methanol, so the solubility in cold benzene is less than that of methanol, and thus the two can be separated by cold benzene method.

(2) alkaloid salts: different alkaloids and different acids to generate the salt is also different solubility: such as ephedra in the separation of ephedrine, pseudoephedrine, that is, the use of the two oxalate water solubility is different, extracted and processed toluene solution obtained by the oxalic acid solution after extraction and concentration, oxalic acid ephedrine solubility is small and the precipitation of crystals, oxalic acid pseudoephedrine solubility is large and stay in the mother liquor.

3. Separation using special functional groups

(1) Phenolic or carboxyl group-containing alkaloids become salts soluble in water under alkaline conditions, and can be separated from general alkaloids.

(2) Lactone or lactam structure of alkaloids can be heated in alkaline aqueous solution to open the ring to generate carboxylate dissolved in water and separated from other alkaloids, and then ring synthesize the original alkaloids under acidic and precipitate.

4. Separation by chromatography

(1) Adsorption column chromatography: alumina or silica gel is commonly used as adsorbent, and sometimes cellulose and polyamide are also used.

(2) Distribution column chromatography: for certain alkaloids with particularly similar structures, distribution chromatography can be used.

(3) Other: high-performance liquid chromatography, preparative thin-layer chromatography, dry column chromatography, medium-pressure or low-pressure column chromatography, etc. are also commonly used to separate alkaloids.