Pharmaceutical Analysis and Quality Control
Core concepts
Candidates must understand the analytical techniques used to assure drug identity, purity, potency and stability. Know the principles and applications of titrimetry (acid–base, redox, complexometric), UV-Vis spectrophotometry (Beer–Lambert law, molar absorptivity), chromatography (TLC, HPLC with UV detection, GC for volatiles), and spectroscopy (IR for functional groups, NMR for structure, MS for molecular mass). Understand pharmacopoeial method validation parameters: accuracy, precision, specificity, linearity, range, limit of detection and quantitation, robustness. Know the difference between identification tests, limit tests (e.g. for chloride, heavy metals) and assay. Understand dissolution testing, content uniformity, and stability testing (ICH conditions, shelf-life determination).
Traps
Questions exploit confusion between LOD and LOQ, between precision and accuracy, and between a specific and a selective method. Another trap is applying Beer–Lambert outside its linear range, or assuming HPLC retention time alone confirms identity (it confirms identity only with a reference standard and/or a second method). Titration endpoint vs equivalence point is a common distractor.
Rule of thumb
For any validation parameter question, match the definition to the term: accuracy = closeness to true value; precision = reproducibility; specificity = ability to measure the analyte in the presence of impurities. For method selection, ask 'is the analyte volatile (GC), chromophoric (HPLC-UV), or a simple acid/base (titrimetry)?'
Worked example
Assay of a weak acid tablet by acid–base titration: dissolve, titrate with standard NaOH to a phenolphthalein endpoint, and calculate percentage content from the titre volume, molarity and equivalent weight. The equivalence point must lie within the steep part of the titration curve for the indicator to be valid.