Quality and Analytical Testing Questions and Answers

COAs, HPLC, mass spectrometry, purity, stability and supplier verification.

108 deduplicated search questions in this category, answered by 7 in-depth guides.

In-depth answers

What Should a Peptide Certificate of Analysis Contain? A peptide certificate of analysis should identify the batch and the sequence, then report measured results for purity by HPLC, identity by mass spectrometry, water content, counter-ion content and appearance. Every result needs the method it was obtained by and the limit it was judged against. Without the accompanying chromatogram and mass spectrum, a COA is a claim rather than evidence. How Do You Read an HPLC Chromatogram for a Peptide? Read an HPLC chromatogram from the method first, then the picture. The x-axis is retention time in minutes and the y-axis is absorbance in mAU, usually at 214 or 220 nm for a peptide. Purity is the main peak area divided by the total integrated area, so the gradient, wavelength and integration threshold decide the number as much as the chemistry does. How Do You Read a Peptide Mass Spectrum? A peptide mass spectrum plots mass-to-charge ratio against intensity. In electrospray, one peptide appears as a series of peaks at different charge states; the spacing between them gives the charge, and software converts the envelope into a single neutral mass. In MALDI the peptide usually appears as one singly charged [M+H]+ ion. Identity is confirmed when the measured mass matches the sequence within a stated ppm error. How Is Peptide Purity Tested? Peptide purity is tested by reversed-phase HPLC, which reports the target peak as a percentage of total integrated peak area, and by mass spectrometry, which confirms that the main species has the expected mass. Purity is not peptide content: content also requires water, counter-ion and assay data. A complete claim combines HPLC area percent, identity, water by Karl Fischer and an assay such as amino acid analysis. How Do You Verify a Peptide Supplier? Verify a peptide supplier in four steps: confirm the legal entity and address, request the COA with its chromatogram and mass spectrum for a specific lot, test whether they can re-test that lot and explain deviations, and compare the documents for internal consistency. A manufacturer can describe the batch it made. A reseller who never saw the batch answers every technical question with a brochure. What Quality System Should a Peptide Supplier Have? A peptide supplier should operate a documented quality system covering specification setting, batch records, release testing, deviation and change control, retention samples and supplier qualification. ISO 9001 certifies the management system, not the product. GMP applies to drug substance manufacture under regulatory inspection and is not implied by the phrase "GMP-grade". Always ask for the scope of a certificate. How Is Peptide Stability Tested? Peptide stability is tested by storing the material under defined conditions and measuring the same critical attributes over time: appearance, HPLC purity, identity by mass, water content and, for solutions, pH. Forced degradation studies show which stress pathways matter. Accelerated studies estimate sensitivity, and real-time studies at the intended storage condition support the retest date.

All quality and analytical testing questions

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