Bioburden, Sterility and Pyrogens: Three Different Tests
Three terms get used interchangeably and they measure three different things. The distinctions are worth holding because a material can pass one and fail another…
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How research peptide identity and purity are verified, and how to read the supporting analytical documentation.
Three terms get used interchangeably and they measure three different things. The distinctions are worth holding because a material can pass one and fail another…
A mass spectrum returns a number, and a certificate compares it to a calculated one. How close they need to be before the comparison means something depends on what the instrument…
A certificate sometimes quotes a calculated mass that does not match the number in a reference database, and both are correct.
Small molecules are often separated with a fixed mobile-phase composition. Peptides almost never are.
HPLC establishes what proportion of the peptidic material is the target sequence. It cannot establish how much of the solid in the vial is peptide at all.
A lyophilised peptide is dry, but dry means free of water rather than free of everything. Synthesis and purification use organic solvents…
An autosampler injects one sample after another through the same needle, loop and tubing. When traces of the previous sample remain and appear in the next chromatogram…
Two analysts given the same chromatogram will not always produce the same purity figure. The trace is fixed; the areas are not.
There is a difference between an impurity being absent and an impurity being invisible, and a purity figure does not distinguish them. Two thresholds govern which is which.
Nearly every peptide purity figure you will ever read came off a C18 column. It is the default for good reasons…
Certificates report purity to one decimal place. The implied precision is almost never justified…
A certificate reporting a measured mass does not usually say how the mass was obtained. It matters, because the two techniques in common use produce different spectra…
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