Pharmaceutical chemistry and pharmaceutical analysis, including quality control
What the exam tests
This domain tests pharmacopoeial quality control: identity, assay, impurities, uniformity, dissolution, sterility, and validation. You must be able to interpret specifications and perform common calculations accurately.
Core rules
- A specification states the test, method, limits, and acceptance criteria; results must be compared with the registered specification and pharmacopoeial requirements.
- Identity tests confirm the substance; assay quantifies it; impurity tests limit degradation products and residues.
- Analytical methods must be suitable for purpose. Validation covers specificity, linearity, accuracy, precision, range, and robustness.
- Reference standards, calibrated instruments, and documented sample handling are essential for traceability.
- Results calculated on the dried or anhydrous basis must state the basis used.
Worked example
A 0.9% sodium chloride sample is assayed by argentometric titration. A 10.0 mL sample consumes 15.4 mL of 0.1 M silver nitrate; 1 mL of 0.1 M AgNO3 corresponds to 5.844 mg NaCl. Is the sample compliant?
Reasoning: mass of NaCl = 15.4 × 5.844 mg = 90.0 mg in 10.0 mL. That is 9.0 mg/mL, or 0.90 g per 100 mL, which meets the 0.9% label claim. State the calculation basis, the endpoint, and the acceptance range. A result near the limit requires attention to burette reading, indicator, and sample volume.
Traps that cost marks
- Calculating on the wrong basis, such as ignoring loss on drying.
- Mixing molarity and normality without checking the equivalence factor.
- Using an expired reference standard or an uncalibrated balance.
- Reporting a single injection result without system suitability or replicate requirements.
- Confusing pharmacopoeial limits with internal alert limits.
Exam focus
Write the formula, substitute units, and state compliance against the registered specification.