EMMS-1: Enriched methylmercury isotopic certified reference material

Certified values for isotope amount ratios, isotope abundances and atomic weight of mercury have been established for this 198Hg-enriched methylmercury isotopic reference material (EMMS-1). These are listed in the table below.

Certified values are based on the unweighted mean of fourteen sets of measurement results generated at NRC. The expanded uncertainty (UCRM) in the certified values is equal to UCRM = kuc where uc is the combined standard uncertainty calculated according to the JCGM Guide and k is the coverage factor. The value of uc is determined from the combined uncertainties associated with the analytical method (uchar) and with homogeneity (uhom). A coverage factor of two (2) was applied. It is intended that UCRM encompasses the uncertainty of every factor that reasonably contributes to the total uncertainty of the measurand.

Table 1: Certified Quantity Values

Isotope mass number, A Isotope amount ratio,
Isotope abundance,
196 0.06(4) 0.0019(11)
198 32.1(1.4) 0.9645(31)
199 0.03(1) 0.0008(4)
200 1 (exact) 0.0300(12)
201 0.07(1) 0.0020(3)
202 0.02(2) 0.0007(5)
204 0.004(3) 0.0001(1)
Atomic weight, Ar(Hg) 198.033(4)

All data pertinent to the certification are available upon request. The mass fraction of mercury in the ampouled solutions of 198Hg-enriched methylmercury is approximately w(Hg) = 4.3 µg/g.

Intended Use

This certified reference material is intended for the calibration of instruments and evaluation of analysis methods for the determination of methylmercury.


Guidelines for CRM producers suggest all sources relevant to the user of the material should contribute to the uncertainty of the certified value. Included in the overall uncertainty estimate are uncertainties associated with the batch characterization (uchar) as well as uncertainties related to possible between-bottle variation (uhom). Potential instabilities due to long-term storage and transport were not considered, as it is believed that the effects of such event would not be isotope specific.

Date of issue: July 2013
Date of expiry: July 2023
Revised: March 2016 (editorial update)

Date modified: