Pharmaceutical Analysis and Instrumental Methods
Pharmaceutical Analysis and Instrumental Methods tests method selection, validation, and data interpretation for drug substances and products. The exam emphasizes whether a method is fit for purpose, not only whether it produces a number.
Core rules
- Validation parameters: accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. LOD is approximately 3.3σ/S and LOQ approximately 10σ/S, where σ is the standard deviation of the response and S is the slope.
- HPLC: reverse-phase separates by hydrophobicity; gradient elution changes mobile-phase strength; system suitability checks tailing factor, resolution, plate count, and relative standard deviation.
- GC suits volatile and thermostable analytes; derivatization extends scope. UV-Vis follows Beer–Lambert, but matrix absorbance and stray light cause deviation.
- Internal standards correct injection volume and extraction variability in bioanalysis; external standards do not.
Worked example
A calibration curve for a drug has slope 0.050 AU per µg/mL and residual standard deviation 0.0015 AU. LOQ = 10 × 0.0015 / 0.050 = 0.30 µg/mL. Reasoning: use the residual standard deviation from the calibration, not the standard deviation of a single blank. Report LOQ with accuracy and precision data; a calculated LOQ that cannot be measured reliably is not acceptable.
Traps
Confusing LOD with LOQ; reporting precision as accuracy; using a calibration range that omits the specification limit; ignoring matrix effects in LC–MS/MS.