IAEA-450 , Platinum and trace elements in algae

Organic , Vegetation

The IAEA-450 CRM is a unicellular microalga (Scenedesmus obliquus). Two batches of algae were grown in an outdoor bioreactor, one batch on a standard nutrient solution (natural contamination level), the second batch on a nutrient solution containing elevated levels of As, Cd, Cr, Hg, Ni, Pb, and Pt. After harvesting, the bulk material was gamma ray irradiated at the IAEA’s laboratories to avoid a bacterial deterioration, and tested for homogeneity.
Thereafter, in order to adjust the Pt mass fraction to the level of environmental pollution in road dust, the two materials were mixed in a ratio of 1:100 (high Pt: low Pt). Using high purity methanol, slurries of the two algae materials were produced and merged under constant stirring in 200 g batches. After 72 hours drying at 60°C, the dry material was homogenized using a shaking device for 8 hours. Then the bulk material was combined/mixed into one batch and homogenized for 1 week in a 50 L drum homogenizer containing 20 ceramic balls of 2 cm diameter.
Bottling of IAEA-450 was carried out under normal laboratory conditions. Portions of 10 g were filled into plastic bottles, sealed with security polyethylene caps and labelled with the code IAEA-450.
After bottling, the material was
sterilized by gamma-ray irradiation with a total dose of 25 kGy using a 60Co source according to EN ISO 13485:2003 in an irradiation facility.

Certified values for mass fractions: platinum and trace elements
(based on dry mass)

Analyte  Certified value*
[mg kg-1]
Standard uncertainty**
[mg kg-1]
As 0.102 0.007
Cd 0.158 0.010
Cr 1.48 0.12
Hg 0.104 0.012
Ni 0.82 0.10
Pb 0.98 0.07
Pt 0.074 0.004

* The certified values are given as total mass fractions of listed elements.
**The uncertainty is expressed as a combined standard uncertainty with a coverage factor k = 1 estimated in accordance with the JCGM 100:2008 Evaluation of measurement data — Guide to the expression of uncertainty in measurement and ISO Guide 35 'Reference materials - General and statistical principles for certification.

This material was thoroughly characterized by group of national metrological laboratories. The certified mass fractions are based on measurement results obtained from national metrological laboratories using validated methods with known accuracy and sufficiency traceability. ICP MS technique was mainly used by all laboratories and applied isotope dilution techniques wherever applicable. INAA technique was used by few laboratories for As, Cr measurements.

The certified values were derived as an Algorithm A as described in Annex C of ISO 13528. Mean and median were also calculated for comparison purposes. These values were compared with the calculated respective Algorithm A values and no significant difference was observed which ensures reliable estimation of assigned value.

The uncertainties associated with the reference values were calculated according to the JCGM 100:2008 Evaluation of measurement data - Guide to the expression of uncertainty in measurement and ISO Guide 35. The combined uncertainty of the certified values consists of uncertainty components associated with characterization (uchar), between bottle heterogeneity (ubb) and stability (ustab). These different contributions were combined to estimate the standard uncertainty.

The quantity values assigned to the certified reference material are mass fractions of specified elements, expressed in the derived SI unit mg kg−1. Values were derived from individual results reported by the metrological institutes through CCQM(BIPM) key comparison/pilot studies. Evidence on metrological traceability to the SI Units was provided for all results taken into account for the calculation of the assigned values.The details concerning the criteria for qualification as certified value may be found in the internal report NAEL/RM/002 ‘Certification of mass fractions of platinum and trace elements in CRM IAEA-450 (algae) sample’, Vienna, September 2015 (attached).

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