Reading a lab test

A certificate of analysis reports what a laboratory measured, on a named lot, by named methods, on a stated date, against a stated specification. Each of those five elements is load-bearing. Remove the lot and the document describes no particular material. Remove the method and the results cannot be compared with anyone else’s. Remove the specification and a number has nothing to be judged against.

The document is evidence about a quantity of material, and its scope ends at the moment of testing. It says nothing about the material after it left the laboratory, which is a matter of storage and transit.

Work down the header before looking at any result. Most defective certificates fail in the header, and a result read out of a defective header is not worth evaluating.

Each method answers one question and is blind to the others. The value of an expanded panel is not thoroughness for its own sake, it is that the blind spots of one method are covered by another.

Purity by HPLC is a proportion of detected absorbance area within a single chromatogram. The denominator is everything that method detected, not everything in the vial. Anything that does not absorb at the detection wavelength, does not retain on the column, or elutes with the solvent front is excluded from both numerator and denominator.

Water, counterion, inorganic salt and endotoxin all fall into that category. This is the single most consequential thing to understand about a peptide certificate, and it explains how two vendors can both report 99% purity for materially different material.

It also means purity figures are comparable only when the methods are. A shallower gradient resolves more impurities and usually lowers the reported figure. A detection wavelength of 220 nm instead of 214 nm changes the relative response of impurities. A vendor reporting 99.5% with an undisclosed method has told you less than one reporting 98.4% with the full method printed.

The most common defect in this category is a certificate that is real, accurate and entirely disconnected from the vial it is attached to. A laboratory tested a sample of some lot at some point, the report was saved, and the same file is now linked from a product page that has sold through many subsequent lots.

Nothing in that document is false. It is simply evidence about material the customer does not have. A lot / batch is the unit that testing applies to, because a later synthesis of the same sequence is a separate event with its own impurity profile, its own residual solvent and its own content figure.

Our lab reports are issued by a named independent laboratory and published exactly as issued. Each one opens at the laboratory itself with the laboratory’s own key, so you are reading the original rather than a copy that could have been edited. Most of this category publishes a PDF and asks to be trusted; ours can be checked at the source.

The report sits on the product page beside the target specification, never merged with it: the specification is the standard the material is made to, the report is what the laboratory measured. Every unit is assigned to a lot at fulfillment and the lot is recorded against the order, read off the vial label rather than a pick list, so the lot number on the vial traces back to what we shipped.

Reports and lot records stay published after stock sells out. A library that only shows current stock cannot be audited backwards, and the ability to check what we published a year ago against what we publish now is the point of publishing at all.

It is a record of measurement on a sample, and a sample stands for the lot only if it was drawn representatively. It describes the lot at the test date and not afterwards. It reports the assays performed and is silent, not reassuring, about every attribute that was not tested.

Most importantly, an analytical result is a statement about composition. It is not an assessment of suitability for any purpose, and it does not change what these materials are supplied for.