99% pure. But how much is actually there?

What the percentage describes

Chromatography separates components under specified conditions. When purity is expressed as area percent, it describes an assigned signal’s share of the evaluated signals. It is not automatically the mass fraction of every substance in a vial.

Detection and separation depend on the procedure. Analytical validation therefore distinguishes different purposes and performance characteristics. A number without methodological context says less than its decimal places might suggest.

Further reading: ICH Q2(R2) · Validation of analytical procedures

Content answers a different question

Content may be stated in milligrams per vial. You need both declared and measured amounts, with their units. Milligrams per vial and milligrams per millilitre are not interchangeable.

Consider a worked example: the label states 10 mg and the report measures 8 mg. The difference is (8 − 10) ÷ 10 × 100 = −20%. A separate purity result of 99% does not change that calculation. Whether a difference is acceptable depends on specifications, procedure and, where relevant, measurement uncertainty.

Identity needs a documented finding

An amount does not fully establish identity. Look for an explicit identity finding and the method used. Do not assume “confirmed” merely because the expected product name appears in the heading.

LC-MS can provide molecular-mass evidence and help assign a compound. The scope of the conclusion depends on the analysis. Record what the report actually supports. PeptidScout’s current methodology also treats identity as a separate criterion.

Further reading: Methodology 1.0

What those measurements leave open

Purity, content and identity do not automatically establish sterility, endotoxin levels or the absence of every possible contaminant. An additional test addresses its own question. An empty field is not a measured zero.

For endotoxin results, retain the units, method and reported limit. “Below the detection limit” does not mean mathematical zero. FDA guidance addresses endotoxin testing as a distinct procedure with sampling and method requirements. It does not authorise a research product for human use.

Further reading: FDA · Pyrogen and Endotoxins Testing (2026)

Make a report easier to compare

Create four rows: purity, content, identity and additional tests. Record the original value, unit and source in each. Use “not documented” when information is absent, rather than leaving an ambiguous blank.

For blends, record each declared component separately. A matching total can conceal a different component ratio. A single percentage does not automatically tell you how much of each component is present. Compare the individual findings before drawing an overall conclusion.