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Why does my CoA say presumptive identity?
The short answer
Because identity was established by retention time: your sample eluted at the same point as a reference standard under the same method. That is strong evidence, but different molecules can co-elute, so it stays presumptive. Only a mass-spectrometry match confirms identity by molecular mass. A certificate saying presumptive is being precise, not evasive.
In detail
Chromatography separates by physical behaviour. When your sample and a known standard emerge at the same time under identical conditions, they are very probably the same compound — but the technique cannot exclude a different molecule that happens to behave identically.
Mass spectrometry measures molecular mass directly, which closes that gap. On our tariff it is a €79 add-on that adds five to seven days.
The wording is a quality signal in itself. A report that claims confirmed identity from retention time alone is either using loose language or overstating what it measured.
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