Category: Analytical Methods

How aspartimide forms at Asp residues during peptide synthesis, why isoaspartate has the same mass as the target, and which methods can tell them apart.

When short polar peptides elute near the void on C18, HILIC can retain them. How it works, which phases suit peptides, and how it compares to C18.

How to design a scrambled-sequence control peptide, avoid new aspartimide or deamidation motifs, and verify it by MS/MS and HPLC when masses are identical.

UPLC vs HPLC for peptide analysis: how sub-2 micron particles trade pressure for speed and resolution, with a worked scaling example and purity caveats.

How HFBA and PFPA differ from TFA as ion-pairing reagents in peptide HPLC: added retention for basic peptides, selectivity shifts, and practical costs.

FITC, TAMRA and Cy dye peptides: added masses, 5/6-isomer doublets, N-terminal FITC truncation and why detection wavelength changes purity numbers.

Where ghost peaks, baseline drift and other artifacts in peptide HPLC come from, how blank runs diagnose them, and how they can shift a purity figure.

How proficiency testing and inter-laboratory comparisons work: assigned values, z-scores and En numbers, and what they mean for peptide purity labs.

Sodium, potassium and ammonium adducts in peptide mass spectra: exact +21.982 and +37.956 Da offsets, charge-state spacing and the K-versus-oxidation trap.

Edman degradation and tandem MS both read peptide sequence but fail in different places: blocked N-termini, Leu vs Ile, fading cycles and fragment gaps.