Education library

How research peptides are tested, documented and stored — written about what researchers measure and how they measure it.

What peptides are, and why sequence matters — Peptides are short amino-acid chains studied for structure, sequence, binding behavior, and signaling effects in controlled research models.
How to read a COA without getting lost — A certificate of analysis should be read as a batch-specific quality record, not a generic marketing asset.
From amino acids to peptides: the structural basics — Forming a peptide bond releases a molecule of water, so the residues in a chain weigh less than the free amino acids that went into it. The chain also has a direction, and the side chains along it give every position its chemical character.
What research-use-only means on a peptide supplier website — Research-use-only is not a disclaimer bolted to the bottom of a page. It governs how a material may be described and to whom it may be sold: reference materials are described by their characterization data, consumer products by the experience they promise.
Storage and handling basics for research materials — A lyophilized solid and the same peptide in solution are not the same storage problem — solutions are far less stable, and extended storage of them is generally discouraged. Cold, dark and dry each shut down a specific degradation route, which is why the storage log is part of the record rather than housekeeping.
Purity and identity testing: two different questions — Purity asks how much of a sample is the target material; identity asks whether the target material is what the label says.
Why peptide HPLC runs at 214 nm and what 280 nm hides — The detection wavelength decides what a chromatogram can see. At 280 nm a peptide without tryptophan or tyrosine is close to invisible, and so is an impurity — which is why a purity figure is meaningless without the wavelength attached.
TFA or acetate: why the counter-ion is not inert — The salt form a peptide arrives as changes its weight, and in cell-based work it can change the result. Trifluoroacetate is cytotoxic at nanomolar concentrations, which is well inside the range a peptide stock delivers.
Why 98% pure does not mean 98% peptide — Purity and net peptide content are different measurements. A vial can be 98% pure and still be roughly a third salt and water by weight, because HPLC purity says nothing about what else is in the vial.
Why a lyophilised peptide is not dry: residual water and Karl Fischer — Freeze-drying removes the water a peptide was purified in; it does not produce an anhydrous solid. Residual water is weighed as peptide, it plasticises the powder enough to move its glass transition, and it is the only component of the vial that changes after the certificate was signed.
Endotoxin and EU/mg: the contaminant no purity test can see — Endotoxin survives steam sterilisation, is not what a sterilising filter is rated to remove, and sits orders of magnitude below anything an HPLC purity figure can resolve. It is measured by a separate assay with its own distinctive failure modes, including one where the assay reports zero and the biology disagrees.
Amino acid analysis: the method that destroys the peptide to weigh it — Net peptide content is determined by hydrolysing the peptide back into free amino acids and counting them. The method is the quantitative reference, and it is also the reason the number carries more uncertainty than the purity figure printed beside it: acid hydrolysis destroys tryptophan outright, so quantitation is limited to 17 of the 20 amino acids.
A matching mass is not a matching sequence — Leucine and isoleucine have exactly the same mass, so no mass spectrometer can tell them apart at any resolving power. They are one of five classes of difference that cost zero daltons, which is why an observed mass matching the theoretical one is evidence about composition rather than confirmation of a sequence.
Why pH decides whether a peptide dissolves: the isoelectric point explained — A peptide that will not dissolve in neutral water is usually not a solvent-volume problem. It is telling you where its isoelectric point sits.