Determination the solubility of drug at room temperature
Aim: To determine the solubility of a drug at room temperature.
Requirements:
Chemicals: 0.01N sodium hydroxide, phenolphthalein indicator, Benzoic Acid, Distilled water
Apparatus: Beaker (250ml)-2, conical flask (100ml)-2, burette, stand, clamp, tile, tripod stand, wire gauze, bulb pipette (5ml), rubber bulb, thermometer, funnel, filter paper.
Principle:
The solubility and dissolution properties of drugs perform a valuable role in the process of formulation development.
Solubility: Solubility is defined in quantitative terms as the concentration of solute in a saturated solution at a certain temperature. Qualitatively, it is defined as the spontaneous interaction of two or more substances to form a homogeneous molecular dispersion. Solubility is commonly expressed as a concentration; for example, as g of solute per kg of solvent, g per dL(100mL) of solvent, molarity, molality, mole fraction, etc. The maximum equilibrium amount of solute that can dissolve per amount of solvent is the solubility of that solute in that solvent under the specified conditions.
Saturated Solution of Drug: It means one in which the drug (solute) is in equilibrium with the solid phase.
Unsaturated Solution of Drug: It means one containing dissolved drug (solute) in concentration below the saturated solution at a specific temperature.
Supersaturated Solution of Drug: It means one that contains more dissolved drug (solute) than necessary for the preparation of the saturated solution at a specific temperature.
Factors Affecting Solubility: 1. Particle size. 2. Temperature. 4. Nature of the solute and solvent. 5. Molecular size. 6. Polarity. 7. Polymorphs.
Importance of Solubility Determination: Drug absorption requires that molecules be in solution at the absorption site. Dissolution of solid dosage forms in gastrointestinal fluids is a prerequisite for the passage of a drug to the systemic circulation following oral administration. The improvement in oral bioavailability is achieved by increasing solubility. Solubility determination is important in the formulation of dosage forms and in deciding the dose of the drug.
Steps involved in solubility determination:
- 1. Preparation of saturated solution of drug
- 2. Filtration
- 3. Analysis for determination of dissolved amount
Techniques of Solubility Improvement: As solubility and permeability are the deciding factors for the in-vivo absorption of the drug, these can be altered or modified by techniques like (A) Physical Modification (B) Chemical Modifications
Procedure:
- Take 50 ml of distilled water in a suitable beaker.
- Add 200mg benzoic acid to the beaker containing water to stir well for 10mins.
- Note the temperature and heat the solution till the temperature increases by 10 degrees from initial temperature.
- Stop heating and cool to room temperature and filter the solution
- Weigh empty conical flask (w1) and transfer 5 ml of the filtered solution to it.
- Take weight of filled conical flask (w2) and titrate against the 0.01N NaOH using Phenolphthalein indicator. End point is colourless to pink.
- Repeat the steps mentioned in 6 and 7 and consider mean of two readings in calculation.
Precautions:
- Determine end point of the titration accurately.
- Use dry filter paper and funnel for filtration.
- Collect filtrate in clean and dry glassware.
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