SI-traceable certification of the amount content of cadmium below the ng g–1 level in blood samples by isotope dilution ICP–MS applied as a primary method of measurement
2001
Diemer, J. | Vogl, J. | Quétel, C. R. | Linsinger, T. | Taylor, P. D. P. | Lamberty, A. | Pauwels, J.
The development and implementation of a method for the certification of cadmium in blood samples at low ng g–¹ and sub ng g–¹ levels is described. The analytical procedure is based on inductively coupled plasma isotope dilution mass spectrometry (ICP–IDMS) applied as a primary method of measurement. Two different sample digestion methods, an optimized microwave digestion procedure using HNO₃ and H₂O₂ as oxidizing agents and a high-pressure asher digestion procedure, were developed and compared. The very high salt content of the digests and the high molybdenum content, which can cause oxide-based interferences with the Cd isotopes, were reduced by a chromatographic matrix separation step using an anion-exchange resin. All isotope ratio measurements were performed by a quadrupole ICP–MS equipped with an ultrasonic nebulizer with membrane desolvator. This sample introduction set-up was used to increase sensitivity and minimize the formation of oxides (less MoO⁺ interference with the Cd isotopes).Because of the very low Cd concentrations in the samples and the resulting need to minimize the procedural blank as much as possible, all sample-processing steps were performed in a clean room environment. Detection limits of 0.005 ng g–¹ Cd were achieved using sample weights of 2.7 g. The method described was used to re-certify the cadmium content of three different blood reference materials from the Community Bureau of Reference (BCR) of the European Commission (BCR-194, BCR-195, BCR-196). Cadmium concentrations ranged between ∼0.2 ng g–¹ and ∼12 ng g–¹. For these materials, SI-traceable certified values including total uncertainty budgets according to ISO and Eurachem guidelines were established.
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