[Patient-adapted, ion selective analysis--characteristics of a new instrument]

We report on a newly developed instrument with ion-selective electrodes (IONOMETER EF) for the measurement of sodium, potassium and calcium. The measurements in whole blood and plasma from intensive care patients were compared with flame photometry. We assessed the precision and accuracy of these measurements. The precision of the analysis is excellent: K+ 4.69 +/- 0.03 mmol/l; Na+ 139.2 +/- 0.27 mmol/l; Ca++: 1.23 +/- 0.03 mmol/l. When assessing the accuracy, the characteristics of the ionselective device have to be considered, as well as differences in solvent volumes, when compared with flame photometry. The correlation coefficient of potentiometric analyses of whole blood and plasma is r = 0.99. It seems to be appropriate to define new normal ranges for ionselective electrode systems.