Automated analyzer for the determination of potassium and sodium in whole blood

Abstract

An automated analyzer for the measurement of potassium and sodium in whole blood has been developed and evaluated. The sensors used in this instrument are the sodium glass and potassium (valinomycin in polyvinyl chloride) membrane electrodes. The features of this system include automatic two-point calibration at fixed intervals or on command, automatic rinsing between measurements, digital display and printout of the emf data, and a sample volume requirement of 0.5 ml. In addition to the evaluation of the response of the system to aqueous and whole blood samples, a study was made of the correlation of data obtained on plasma samples with a flame photometer and the electrometric potassium/sodium analyzer. For both electrodes the correlation was very good ( r = 0.998 for potassium and r = 0.991 for sodium). No anomalous effects were observed with blood samples from normal volunteers, however, no studies were performed with samples taken from patients which might show disease-induced changes in ion-binding properties or interferences from medications. From this study, it appears that the sodium and potassium electrodes are able to meet sensor requirements for a clinical blood-electrolyte instrument. Since an analyzer based on ion-selective electrode technology can determine sodium and potassium in whole blood, such an automatic instrument could be used outside of the central clinical laboratory for stat analyses. While the feasibility of this type of instrument has been demonstrated, much more work is required to establish its performance characteristics for clinical analysis.