01 / Supplier evaluation · 4 min read
How to audit a peptide supplier in one afternoon
You do not need a full site audit to separate a serious supplier from a trading desk. Four requests, all answerable by email, do most of the work.
One lot number, followed end to end. Ask for a released COA and then ask which synthesis record, which purification fractions and which retained sample belong to that number. A manufacturer answers immediately. A reseller has to ask someone else.
The raw chromatogram, not the summary line. A COA that says “purity 98.5 %” is a conclusion. Ask for the integration report, and check whether the impurity peaks are integrated at all and whether the method column and wavelength are stated.
An out-of-specification story. Ask what happened the last time a batch failed release. Every real manufacturer has one. The answer tells you more than any certificate on the wall.
Who signs the release. A name and a role, not a department. If the answer is vague, release is probably not independent of production.
None of this requires a plane ticket. If a supplier resists all four, the site visit will not change the conclusion.
02 / Documentation · 5 min read
Reading a peptide COA, line by line
Most certificate disputes come from reading a result without reading the method attached to it. Five lines are worth checking carefully.
Purity by HPLC. Look for the column, mobile phase, gradient, wavelength and integration threshold. 98.0 % area at 214 nm with a 0.1 % threshold is not the same product as 98.0 % at 220 nm with a 1 % threshold.
Identity by LC-MS. Check the observed mass against the calculated mass for the stated sequence and counter-ion. A one-dalton difference is usually deamidation or a missed reduction step, not rounding.
Peptide content. Purity by area and peptide content by mass are different quantities. A 98 % pure acetate salt can still be 80 % peptide by weight.
Water content. Karl Fischer results explain most discrepancies between two laboratories weighing the same powder.
Counter-ion. TFA is common in research grades and undesirable in cosmetic and food applications. If the COA does not state the counter-ion, the specification is incomplete.
03 / Specifications · 4 min read
95 % or 98 %: choosing a purity target you can defend
Purity is the specification people fixate on and the one most often chosen by habit. The right target depends on what the impurity is, how the material is used, and what your customer will ask for.
What the impurity is matters more than how much. A 95 % lot whose 5 % is water and acetate can outperform a 98 % lot carrying 1.5 % of a deletion sequence.
Application sets the floor. Research-grade material tolerates more than a cosmetic active at 1 % in a leave-on formula, and a food ingredient meets a different limit set entirely.
Cost scales non-linearly. The last impurities are the structurally similar ones. Before specifying 98 %, confirm that the customer’s assay can distinguish it.
Write the method into the specification. “≥ 98.0 % by RP-HPLC, C18, 214 nm, threshold 0.1 %” is a specification. “≥ 98 %” is an invitation to argue.
Editorial note: these notes describe general analytical practice for peptide raw materials. They are not regulatory advice for a specific market, and they make no claim about the efficacy of any ingredient.
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