Development of high accuracy methods for the certification of calcium, iron, magnesium and potassium in human serum

High accuracy methods were developed for the measurements of calcium, potassium, iron and magnesium in human serum using standard addition and isotope dilution mass spectrometry methods. The results were comparable to those obtained by other national metrology institutes and designated institutes as demonstrated in an inter-laboratory comparison. The methods were then adopted for the assignment of reference values in a human serum material and the uncertainties associated with the certified values were obtained by combining the uncertainty components from the characterisation, homogeneity and long-term stability of the materials. The certified values are traceable to the International System of Units and the material can be used by the clinical testing laboratories to validate their methods or as a quality control material to improve the accuracy of their measurements.