The U.S.P - 9th Edition (pg444)
Tinctures are alcoholic preparations made by extracting the valuable principles from drugs by the use of appropriate menstrua or solvents. Tincture of ferric chloride and tincture of iodine are exceptional, not being made by extraction; they are alcoholic solutions of chemical substances.
Tinctures of potent drugs are made of the strength of ten grammes of drug in one hundred mils of tincture. The other tinctures vary in the proportion of drug in the finished tincture.
Tinctures are made by percolation with few exceptions. Maceration or solution is preferred when from its physical character the drug is not suitable for percolation.
The majority of official tinctures are prepared under one or the other of the two type processes described, and in each formula directions are given as to the process to be followed with such modification as may be necessary. A number of drugs require special manipulation for the preparation of satisfactory tinctures, and for those the formulas in full will be found in the text.
Where it has been found possible and desirable to standardize the tinctures a rubric and assay have been added.
Tinctures should be stored in tightly-stoppered bottles, kept in a cool place, and protected from light.
Type Process P-Percolation
Moisten the powdered drug or mixed drugs designated in the formula with a sufficient quantity of the prescribed menstruum to render it evenly and distinctly damp, transfer it to a percolator, and, without pressing the powder, allow it to stand well-covered for six hours; then pack it firmly, unless otherwise directed, and pour on enough of the menstruum to saturate the powder and leave a stratum above it. When the liquid begins to drop from the percolator, close the lower orifice, and, having closely covered the percolator, macerate for twenty-four hours. Then allow the percolation to proceed slowly, gradually adding sufficient of the menstruum to make one thousand mils of finished tincture.
Modification for Assayed Tinctures-In Tinctures that are directed to be assayed, allow the percolation to proceed until the percolate measures nine hundred and fifty mils. Assay a sample of this percolate as directed and from the alkaloidal content thus determined, ascertain by calculation the amount of alkaloids in the remainder of the liquid and add to this enough of the menstruum to make the finished Tincture, conform to the required alkaloidal standard.
Type Process M-Maceration
Macerate the drug or mixed drugs designated in the formula in a stoppered container, in a moderately warm place, with seven hundred and fifty mils of the prescribed solvent (unless a different amount is specified in the formula). Continue the maceration with frequent agitation during three days or until the drug is practically extracted, transfer the mixture to a filter and, when the liquid has drained off completely, gradually wash the residue on the filter with enough of the solvent to make one thousand mils of finished tincture.