Selenium Enriched Yeast Certified Reference Material
CERTIFIED VALUES (milligram/kilogram)
Total Selenium 2059 ± 64
Selenomethionine 3431 ± 157
Methionine 5758 ± 277
This certified reference material is intended for the calibration of instruments and evaluation of methods for the determination of SeMet, Met, and total selenium in yeast or materials of a similar matrix. The material is not intended for nutritional, medical or diagnostic use as its safety has not been established.
Storage and Sampling
To ensure the stability of the SeMet and Met it is necessary to store this material at a temperature of -20°C. Prior to use, the bottle should be rotated and shaken to ensure the contents are well mixed. The bottle should be tightly closed thereafter and returned to -20°C storage.
Preparation of SELM-1
A dry commercial selenized yeast sample (yeast grown in Se rich media) was used for the preparation of this CRM. No additional screening or blending was used. The material was bottled ‘as is’. The material was bottled in cleaned amber glass bottles at an 8g nominal weight. During bottling argon gas was used to flush the
headspace of the vials to displace air. After bottling the material was sterilized by
subjecting it to a minimum dose of 25 kGy gamma irradiation at the Canadian Irradiation Centre, Laval, Québec.
Instructions for Drying
A separate aliquot of the sample should be used to obtain a dry weight correction factor. Drying for 4 days in a freeze-dryer has proved to be a relatively simple method to achieve constant weight.
New guidelines for CRM producers suggest all sources relevant to the user of the material should contribute to the uncertainty of the certified value [2,3]. Included in the overall uncertainty estimate are uncertainties associated with the batch characterisation (uchar), uncertainties related to possible between-bottle variation (uhom) as well as instability derived from effects relating to longterm storage and transport (ustab). Expressed as standard uncertainties these components
can be combined as:
uc(CRM)2 = uchar2 uhom2 ustab2 (1)
Results for the various statistics used to calculate the certified values are shown in
Property values were determined by isotope dilution GC-MS and isotope dilution LC-MS (SeMet and Met) and by isotope dilution ICP- MS and ICP-OES for total Se. All measurements contributed to this certificate were conducted by Chemical Metrology personnel at INMS NRC Ottawa. The characterisation uncertainties (uchar) were calculated in accordance with equation 2,
uchar = s/p0.5
where s is the standard deviation of the means and p is the number of mean results included in the calculation. The calculated uncertainty components related to the characterization of SELM-1 are reported in Table 2.
keywords: Foodstuff, Speciation analysis, Selenium speciation