Pharmaceutics Laboratory
Saturate a solvent with excess drug at a controlled temperature, filter and evaporate an aliquot to find the solubility; then run a paddle dissolution test, withdraw samples on time, read them on a spectrophotometer and build the dissolution profile with the sampling correction.
Equilibrium solubility is the concentration of a saturated solution in contact with excess undissolved solid at a stated temperature. If no solid remains, the solution is not known to be saturated — only that everything you added dissolved.
The shake-flask method agitates excess drug in the solvent at constant temperature until equilibrium, then samples the clear solution at that temperature (a cold syringe can crystallise drug out), and measures it — here gravimetrically, by evaporating an aliquot and drying the residue to constant mass.
Published data (Granberg & Rasmuson, 1999): paracetamol dissolves to 12.78 g/kg water at 20 °C, 14.90 at 25 °C and 17.39 at 30 °C — 'sparingly soluble' in the USP's descriptive terms.
Dissolution is the RATE at which drug leaves a dosage form. This activity is modelled on the USP Acetaminophen Tablets test (paddle, 50 rpm, 900 mL pH 5.8 phosphate buffer at 37 °C, Q = 80 % in 30 min). Samples are filtered, diluted into the calibration range and read at ~243 nm; each withdrawn sample removes drug, which the calculation adds back.
Sink conditions (medium ≥ 3 × the volume the dose would saturate) keep the dissolution rate from being limited by solubility — which is why the solubility is measured first.
SIMULATION: the release profile, absorbance noise, calibration line and drying behaviour are teaching models with stated values. This is not a pharmacopoeial test and makes no compliance claim.
Paracetamol (acetaminophen) · Purified water · Paracetamol 500 mg tablets · pH 5.8 phosphate buffer
Curriculum
Solubility is listed in UoK PHC-406 (2nd year, 2nd semester: solubility of benzoic acid) and HEC Physical Pharmacy I (“Solubility determination techniques”); dissolution by USP paddle/basket is listed in UoK PHT-701 (5th year, 1st semester) and PHT-614, not in UoK's Physical Pharmacy lab. Paracetamol is our illustrative choice. Not faculty-reviewed.
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Simulated practice: results come from teaching models and illustrative data described on this page. Nothing you enter is sent anywhere unless you are signed in, in which case your completion is added to your progress.
