An improved reference method for serum cations measurement by ion chromatography

BACKGROUND: To improve the accuracy of the routine methods in laboratory medicine, ion chromatography with a simple sample treatment procedure, which can completely remove the proteins and/or organics in human serum, has been developed for the determination of serum cations. METHODS: Chromatographic conditions for the separate and simultaneous determination of K, Na, Ca, and Mg were investigated. Furthermore, various factors influencing the mineralization of human serum, such as the selection and amount of oxidant, were also examined systematically and optimized. RESULTS: The optimized experimental conditions are as follows: 1.0 mL of serum specimen digested with 2 mL nitric acid (120°C) followed by 2 mL hydrogen peroxide (80°C). The specimens were then redissolved and determined by ion chromatography under the optimum eluent concentration of 32 mmol/L methanesulfonic acids. The measurement accuracy and precision are less than 1.0% for all the analytes by analyzing NIST certified reference materials, IFCC-RELA specimens and serum specimens. The results were also comparable with the reference values obtained by the inductively coupled plasma mass spectrometry (ICP-MS), which were found to be in good agreement. CONCLUSIONS: Ion chromatography with a simple sample treatment procedure for the determination of cations in human serum with high sensitivity and specificity was developed. The proposed method could be recommended as a candidate reference method for the determination of serum cations.