SIG — independent test log

How to read this table

Three columns matter and they are easy to conflate. Claimed is what the vendor documentation said. Result is what an independent service measured on a vial a member actually received. The gap between them is the only number on this page with any predictive value — the absolute purity figure tells you much less than whether the vendor's own claim survives contact with a lab.

A vendor claiming 98% and delivering 98% is more trustworthy than one claiming 99.5% and delivering 98.6%, even though the second vial is nominally better. Consistency beats peak performance when you cannot test every order.

Also note what this table is not: it is not a survey. These are retail-quantity purchases by individual members, self-selected, self-funded and self-reported. SIG has 6 entries here; the vendors with more entries look more variable partly because more sampling reveals more variance.

What SIG claims

The Claimed column comes from the documentation SIG publishes with each lot. If you want to read those claims at source before comparing them with the measured column, they are on the storefront.

Read SIG’s own documentation at sigmaaldrich.org →

Services used

All four independent services appear across the vendor directory: Janoshik (HPLC and mass spec, the most-used by members), Medutest, PeptideMeter (which also publishes vendor-level trend data) and VendorInvestigate. Where two services tested the same batch we list both rows rather than averaging them, because the disagreement is the interesting part.