Percolation

Q: What is percolation?

Ans: Percolation is the package of the raw material into a column and the solvent is allowed to percolate through it.

Although some materials may be packed into a percolator in the dry state e.g. Ginger, most drugs require preliminary moistening.

Q: What is the principle of percolation?
Ans: It is a process in which a comminuted drug is extracted of its soluble constituents by the slow passage of the suitable solvents through the column of a drug.

Q: What do you know about percolator and percolate?
Ans: The drug is packed in a special extraction apparatus termed as percolator with the collective extractive called the percolate.

Q: What is preliminary moistening?
Ans: The solid material is mixed with sufficient amount of solvent and the moist mass is allowed to stand for 4 hours in a well-closed vessel. This is preliminary moistening.

Q: Why preliminary moistening important?
Ans: This preliminary moistening is important because the dried tissues may swell on contact with the solvent and if packed in the dry condition subsequent swelling might decrease the porosity of the material and choke the column.

Preliminary moistening also makes the fine particles less liable to be washed out of the column during percolation.

Q: Defined the methods of percolation?
Ans: There are two methods of percolation which are given below:

• Commercial scale

• Small scale

Q: What is the commercial method for the percolation?
Ans: The drug is supported on a preforated metal plate covered with sacking or straw. The top of the apparatus is removable and provided with portholes for inspection and running in of solvent. At the base the outlet is fitted with a tap and a pipe leads the top of a second percolator in order to use the solvent more efficiently.

Q: What is the small scale method for percolation?
Ans: On small scale glass percolators can be used and the raw material is supported in a loose plug of tow or other suitable substance which has been previously moistened with solvent.
Q: What is reserved percolation?
Ans: Liquid extracts are more concentrated preparations than tinctures and percolation to exhaustion will produce a preparation that is much diluted. It is therefore necessary to decrease the volume of the percolate by evaporation.

In certain instances such as in Liquorice Liquid Extract, the whole of the percolate may be concentrated by evaporation.

Q: How Ipecac syrup is prepared?
Ans: Ipecac syrup is prepared by percolation. It is prepared by adding glycerin and syrup to an extractive of powdered ipecac obtained by percolation.

The drug ipecac which consists of the dried rhizome and roots of Cephaelis ipecacuanha containing emetine, cephaeline and psychotrine. These ingredients are extractive from the powdered ipecac by percolation with the hydro-alcoholic solvent.

Further Reading:
Remington: The Science and Practice of Pharmacy (Remington the Science and Practice of Pharmacy)

British Pharmacopoeia 2010

Textbook of Pharmaceutics