Crystallization

Crystallization is the (natural or artificial) process of formation of solid crystals precipitating from a solution. Crystallization is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.

The crystallization process consists of two major events, nucleation (the solute molecules dispersed in the solvent start to gather into clusters, on the nanometer scale) and crystal growth (subsequent growth of the nuclei that succeed in achieving the critical cluster size). Nucleation and growth continue to occur simultaneously while the supersaturation exists. 

•Single-solvent recrystallization : "compound A" and "impurity B" are dissolved in the smallest amount of hot solvent to fully dissolve the mixture, thus making a saturated solution. The solution is then allowed to cool => different solubility of compounds in solution drops => compound dropping (recrystallizing) from solution. The slower the rate of cooling, the bigger the crystals formed. The solid crystals are collected by filtration.

•Multi-solvent recrystallization: similar to the single-solvent but where two (or more) solvents are used. the proportion of first and second solvents is critical. Possible removal by distillation or by an applied vacuum. 

•Hot filtration-recrystallization: separate "compound A" from both "impurity B" and some "insoluble matter C". 

•Seeding: this can be spontaneous or can be done by adding a small amount of the pure compound (a seed crystal)

Adulteration & Falsification: get the right efficiency

Adulteration means falsification of an extract in terms of origin, assay, extraction, actives, or analysis, mostly in order to improve the price. Well-informed, it's easier to know what to look at ... or look for.

Method of analysis: changing the method or the standard

•UV versus HPLC: except for very few actives / markers, UV methods always give much higher response than HPLC (when the standard exists of course) without being able to find a correlation. This may be versus HPLC, or can be many others, especially when using internal method.

•Wave lengths: a different wave length or the use of a different Specific Absorption Coefficient

•Standard: the use of a different standard for a better response by HPCL (example: a bucket contains 9 balls as petanque balls. considering ping pong balls, it contains 32, and 90 Balls (as marble balls)

•Family of the actives: reference to the global family of the actives instead of the active itself.

•Reduction of the number of markers, what allows to use addition of chemical origin. The more there are markers in the description, the most difficult it is to falsify them.

Plant Extract Ratio: difficult to be sure to get a 4:1 extract when there’s no marker to control. And as well easy to say 20 or 30:1

•NER / PER: voluntary misunderstanding between Native extract and Plant extract, sometimes even considering the original plant, with the water.

Specie: use of a another bionomial origin, of even a plant close to the original plant (same genus)

Part of plant: use of a different part than the one mentioned or recommended (for instance, leaves instead of roots, even partly)

Addition of chemicals: addition of exogenous origin material, from other plants or from chemical process. They can be added to a coloured carrier or sometimes to the plant powder in order to get at least a positive TLC.

Solvents: use of another solvent than the one mentioned for a more selective and efficient extraction.

Geographical Origin: plants may offer a different profile depending on the geographical origin, that you may need specifically. It can be also collected from a non-authorized zone.

Those are some of common noted origins of adulterations you may unfortunately meet.

The raw material - ie. the plant - provides a certain amount of soluble and insoluble part. This means that a repeated process will extract more or less the same amount in the solution, and the ratio cannot be whatever you may request or prefer.

NER / Native Extract Ratio: not always refereed to. This is the Ratio after extraction ie. the ratio of the mass of herbal material to the mass of the resulting native herbal preparation (material consisting only of components present in the original plant or formed during the extraction process, excluding any excipients or other added substances). It should not vary so much since it’s linked the dry matter we can extract (but depends anyhow on solvents, time, etc...)

PER: Plant Extract Ratio, ie. the ratio after process and before addition of any support or external materials. Should be the NER for basic extraction, or much more in case of purification. A high PER without purification could mean a very quick extraction and then using a lot of carrier.

DER: Drug Extract Ratio, ie. the ratio of the end extract versus the plant, between the quantity of herbal substance used in the manufacture of a herbal preparation and the quantity of the herbal preparation obtained