A higher order method for the determination of total phosphorus in human serum

Abstract

Phosphorus is an essential element in the human body and an important clinical biomarker in serum. However, the lack of reference method that is traceable to the International System of Units and matrix-matched certified reference material (CRM) pose a major challenge in the assessment of the accuracy of phosphorus measurements. A higher order measurement procedure for total phosphorus in human serum by standard addition method using high-resolution sector field inductively coupled plasma mass spectrometry was established. In this method, germanium and gallium are used as internal standards. The accuracy of the measurement was evaluated by comparing the results with the certified values of Trace Elements in Tea Leaf Powder (NMIJ CRM 7505-a) and Trace Elements in Milk Powder (NMIJ CRM 7512-a), as well as the reference value of Electrolytes in Frozen Human Serum (NIST SRM 956d). This method had also been applied in an international interlaboratory comparison (CCQM-K139 Elements in Human Serum). The results of this comparison showed that this method is comparable with the methods used by other established national metrology institutes or designated institutes. In addition, the first human serum reference material that is certified for total phosphorus was produced. This reference material is valuable for method development as well as the assessment of the accuracy of phosphorus measurements in clinical laboratories (as quality control).