The ion selective electrode method (ISE) for concentration measurement of the sodium, potassium and chloride has been widely used in field method. However, the measured values from antomated analysis with the ISE could not be corrected accurately. The accuracy transferring in the accuracy-based measurement system could be transfered by definitive methods, ion-exchange gravimetry for sodium, isotope dilution mass spectrometry for potassium and chloride, to the primary serum reference material, and reference method, secondary serum, reference material and ISE for field method. The certified serum reference material (CRM) conforms to the golden standard of undiluted and diluted potentiometry, and it can be solved the problems which results in differences in the measured values between device or facilities. Furthermore, it can be maintained the measured values accuralely by which manufacturers and users can standardize their instruments to give results in concentration which are verifiable to the CRM.
This document offers a protocol the theory of setting the CRM, the data correction, the accuracy control algorithm and the allowable limit.
