How do you compare peptide lab test results between vendors?

What do you line up before comparing two certificates?

• The compound and the labelled amount per vial.
• The measurement: purity, identity or net peptide content. They answer different questions and are not interchangeable.
• The method behind each figure, such as HPLC for purity and mass spectrometry for identity.
• The laboratory, named on the document, with an accession number you can look up.
• The lot number and the test date, so the result is tied to a batch and a moment.

Why can two 99% results mean different things?

A purity percentage is the target peak's share of the total peak area in an HPLC run. Which detector is used, and how the peaks are measured, are part of the method, so a figure only means the same thing as another when the method is the same.

Net peptide content is a separate measurement in milligrams. A high purity percentage does not tell you how much peptide the vial holds, which is why a certificate that reports both is more informative than one that reports a single number.

Does one good result describe a company?

A certificate describes one lot on one test date. It is evidence about that batch, not a rating of the seller. To judge a seller you would look at results across several lots and dates, which is why our certificate library lists every lot we publish rather than a single showcase result.

What does a laboratory actually test?

A laboratory reports on the sample it was sent. The link between that sample and the vial in your hand is the lot number, which is why matching the lot on the vial to the lot on the certificate matters as much as the figures themselves.

Then check the report at the source: enter the accession number on the laboratory's own website and compare the compound, lot, date and results with the copy you were shown.