ORMS-5 is a river water spiked with inorganic mercury. The material is packaged in 50 ml glass ampoules stabilized with 0.5% BrCl.

The certified value was derived gravimetrically and corroborated with two methods of analysis: cold vapour isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) and flow injection cold vapour atomic absorption spectrometry (CV-AAS). The certified value is the unweighted mean of the results ± the expanded (k=2) uncertainty (U_CRM). The results generated by each of these methods were judged to be independent.

The expanded uncertainty in the certified value is equal to U_CRM = ku_c, where u_c is the combined standard uncertainty calculated according to the JCGM Guide and k is the coverage factor. It is intended that U_CRM encompasses every source that reasonably contributes to the uncertainty of the measurand. A coverage factor k=2 is used to give an uncertainty interval that contains roughly 95% of the underlying distribution. The value of u_c is determined from the combined uncertainties of the methods (u_char) as well as uncertainties associated with homogeneity (u_hom).

Intended use

This CRM is intended for the calibration of instruments and evaluation of methods for the determination of mercury.