Analytical method design
Analytical method design: 9 articles from Peptides Info. Handling, storage and laboratory reference.
Capillary Electrophoresis as an Orthogonal Peptide Purity Check
Capillary zone electrophoresis separates peptides by charge-to-size ratio, not hydrophobicity. The separation principle, background electrolyte and pH choice, conditioning and start-up sequence, far-UV detection, reading an electropherogram against a chromatogram, and a reference parameter table for a first method.
D-Amino Acid Content of Peptides: Marfey's Reagent Procedure
How the D-residue content of a synthetic peptide is measured: hydrolysis in deuterated acid to tag racemisation caused by the method itself, derivatisation with Marfey's reagent, achiral LC-MS separation of the diastereomers, and the per-residue % D calculation with its controls.
CD Spectroscopy of Peptides: Set-Up and Molar Ellipticity
Acquiring a far-UV circular dichroism spectrum of a peptide and converting millidegrees to mean residue ellipticity: buffers that do not absorb, pathlength and concentration pairing, the high-tension limit, baseline subtraction, a worked conversion, reference spectra, and why short peptides read as disordered.
Residual Solvents in Lyophilised Peptides: USP <467> Headspace GC
Which organic solvents survive synthesis, purification and freeze-drying, how ICH Q3C classes and limits apply to them, and the USP <467> headspace GC workflow from sample preparation to the limit decision, with a worked ppm calculation for a small sample mass.
ESI-LC-MS Versus MALDI-TOF: Which Mass Measurement Proves What
Two ionisation routes, two kinds of spectrum, and different claims each can support. How electrospray and matrix-assisted laser desorption differ, what mass accuracy in ppm actually requires, and how to choose between them for peptide identity.
Peptide Mapping: Confirming Sequence, Not Just Mass
An intact mass confirms composition; the order of residues needs fragments. How a peptide map is designed — enzyme choice, digestion, LC-MS/MS, coverage — when direct fragmentation of the intact peptide is enough, and what a mapping report should contain.
Reversed-Phase HPLC for Peptides: Column, Gradient, Mobile Phase and Detection Wavelength
How a peptide purity method is built rather than read: stationary phase and pore size, trifluoroacetic acid against formic acid, scouting and focused gradients, temperature, injection and wavelength — with a reference method and a development sequence.
Synthesis-Related Impurities: Deletion, Truncation, Incomplete Deprotection and Racemisation
Solid-phase synthesis produces a predictable family of near-copies of the target. The impurity classes, the mass shift and chromatographic behaviour of each, why a single purity figure can hide them, and what an impurity-aware certificate lists.
System Suitability and Reference Standards: Proving the Instrument Before Trusting the Result
Validation shows a method can work; system suitability shows it worked on the day. The parameters and their formulas, how to build a test for a peptide purity method, and how the reference standard behind it is characterised, qualified, stored and recorded.