Analytical Testing &amp; Quality

Size Exclusion Chromatography and Peptide Aggregate Detection

What size exclusion separates, why apparent molecular weight is not a mass measurement, and which aggregates it detects that a reversed-phase purity trace destroys.

5 min read

Tandem Mass Spectrometry: Reading a Peptide Sequence From Fragment Ions

How MS/MS fragments a selected peptide ion into b and y series, how a sequence is read from the gaps between them, and the three things the spectrum cannot distinguish.

Peptide Mapping: Protease Digestion and Sequence Coverage

How a protease digest confirms residue order, what sequence coverage means, and why a peptide map localises a modification that an intact mass cannot.

Fmoc or Boc: Which Chemistry Built Your Peptide, and What It Left Behind

One strategy separates the two deprotections by acid strength, the other by acid versus base.

Measuring Concentration by Absorbance at 280 Nanometres

Weighing measures the vial. Absorbance measures the peptide. What the extinction coefficient is built from, a worked example, and the sequences where it simply does not work.

Isotope Patterns: What the Shape of a Peak Cluster Tells You

A peak is a cluster, and its relative heights are a fingerprint of elemental composition. How to count carbons and sulfurs from data the instrument already collected.

Why the Same Method Gives Different Numbers in a Different Lab

Dwell volume, column batch, integration settings — a written method is an incomplete description of what actually happens. What the formal transfer exercise tests.

Heavy Metals and Elemental Impurities in Synthetic Peptides

The contamination class a peptide certificate almost never mentions, because nothing in a chromatogram or an intact mass spectrum can see it.

Protecting Groups: The Mass Signatures of Incomplete Deprotection

Right sequence, wrong mass. The increments that identify which side chain kept its group — and why arginine is the recurring offender.

Peak Purity: What a Diode Array Detector Can and Cannot Prove

A pure peak is one compound at every point across it. The test works — except on the impurities most likely to co-elute with a peptide.

Forced Degradation: Breaking a Peptide to Test the Method

Deliberately destroying five to twenty percent of a sample, to find out whether the analytical method can actually see the products it creates.