Category: Analytical Methods

What specificity, linearity, range, accuracy and precision mean under ICH Q2, applied to HPLC purity methods for synthetic peptides, with typical designs.

How racemization forms D-amino acid diastereomers during peptide synthesis, why HPLC and mass spec miss them, and how chiral purity is measured.

What Kd, Ki, IC50 and EC50 each measure, why binding and functional potency figures cannot be compared directly, and how to read them.

How out-of-specification lab results should be investigated, when a retest is legitimate, why averaging hides failures, and what a certificate shows.

What a freeze-dried peptide cake’s appearance can and cannot tell you: collapse, cracks, loose powder, moisture uptake and what the vial mass includes.

How deconvolution turns an ESI charge envelope into a peptide mass, a worked example, the ways it fails silently, and monoisotopic versus average mass.

Why an HPLC retention time is weak identity evidence on its own, what makes it drift, and how a same-run reference standard makes it meaningful.

How circular dichroism reports peptide secondary structure, how to read helix, sheet and disordered spectra, and the sample conditions that distort it.

How net peptide content is measured by amino acid analysis or nitrogen testing, why it differs from HPLC purity, and which residues hydrolysis loses.

How one tested vial comes to stand for many: random, stratified and convenience sampling, the square-root rule, and what a result can claim.