Different questions.
Complementary methods.
Understand what each analytical technique measures, and what its result can tell you.
Chromatographic separation & UV detection
High-performance liquid chromatography separates sample components as they travel through a chromatographic column. UV detection records responsive compounds as peaks. Integrated peak areas provide a defined chromatographic purity measurement.
Reported output
Chromatogram, retention information and principal peak area percentage.
Interpretation matters
Results depend on the method, integration and detector response. Co-elution and compounds without suitable UV response can limit what is observed.
Molecular mass & identity assessment
Mass spectrometry measures the mass-to-charge ratios of ionized molecules. The observed molecular mass is compared with the expected value as part of an identity assessment.
Reported output
Mass spectrum, observed mass and comparison with the declared peptide.
Interpretation matters
Matching molecular mass does not alone resolve all sequence variants or isomers. Further structural work must be specified separately.
Trace elemental analysis
Inductively coupled plasma mass spectrometry detects elements following sample preparation. Lead, arsenic, cadmium and mercury are reported separately with method-specific limits.
Reported output
Element concentrations, units, limits of detection and limits of quantitation.
Interpretation matters
Sensitivity depends on sample preparation, matrix and method validation. Any comparison with a specification must state its basis.
A note on ICH Q3D
ICH Q3D addresses elemental impurities using a risk-based framework, including permitted daily exposures that depend on the route of administration. It is not a universal ppb threshold for research materials. Any derived concentration specification requires a stated basis and applicable assumptions.
Read the ICH Q3D guideline