EPA Method 1631 Mercury Calibration Standard from Japan

> This mercury calibration standard is a solution-based certified reference material with known mercury concentrations at ppb levels, used for validating ultra-trace mercury analysis methods like EPA Method 1631. It is accompanied by a certificate with certified values and uncertainty, qualifying under Chapter Note 2(A). It is not a separate chemically defined element because it is a solution preparation, so it is not excluded by Chapter Note 1(a).