Physical Incompatibilities: Precipitation

Physical Incompatibilities: Precipitation

Precipitation:

  • Definition: Occurs when a solvent becomes insoluble upon the addition of a solution.

  • Mechanism: Solubilized substances may precipitate from the solution if a non-solvent for the substances is introduced.

Examples:

  • Resins: Resins are typically insoluble in water.

    • Observation: An alcoholic solution of resins mixed with water leads to the precipitation of resins.

  • Aqueous Dispersions: High concentrations of alcohol or salts added to hydrophilic colloids can result in precipitation.

    • Illustration: Polysaccharide mucilage combined with high concentrations of alcohol or salts can lead to precipitated colloids.

Effects of Electrolytes:

  • High concentration of electrolytes can cause the cracking of soap emulsions by salting out the emulsifying agents.

    • This often results in reduced effectiveness and stability of emulsified products.

Vehicles for Medicaments:

  • Vehicles consisting of one or more organic liquids are often used to dissolve medicaments with low solubility.

  • However, when these vehicles contain water-soluble adjuvants or inorganic salts, precipitation may occur.

    • Consideration: Careful selection of vehicles can help minimize precipitation issues.

Tinctures and Precipitation:

  • When tinctures containing resinous matter are introduced into water, resin agglomerates form and precipitate diffusely.

  • To mitigate this reaction, it is essential to control the addition process.

    • Technique: Slowly adding the undiluted tincture while vigorously shaking the mixture can prevent undesirable precipitation.

Example of Incompatible Prescription: Lotion of Compound Tincture of Benzoin

  • Ingredients:

    • Tincture benzoin compound – 5g

    • Glycerin – 10ml

    • Rose water up to 100ml

  • Cause of Incompatibility:

    • The presence of resins in tincture benzoin compound causes precipitation due to a change in the solvent system.

    • This reaction may result in unintended alterations in the final product's properties.

  • Remedy:

    • To produce a fine colloidal dispersion and avoid precipitation, the tincture should be added with rapid stirring.

    • This process helps in achieving a stable suspension without the need for additional suspending agents.