Evaluationof an Instrument(Nova-i) for Direct Potentiometric Analysis of Sodium and Potassiumin Blood and Their Indirect Potentiometric Determination in Urine

We evaluatedand compared the Nova-ito an alternative directpotentiometricanalyzer(Orion-SS/30) and to flame photometry (Beckman “KLiNa Flame”). Interassay pre-cision of the Nova-i for plasma was better than flame photometry but slightly worse than the Orion SS/30. For urine, interassay precision of the Nova-i was not as good as for the flame photometer, but adequate for clinical use. Calcium, magnesium, phosphate, pH, uric acid, creatinine, and urea influenced neither sodium nor potassium values. Ammonia did not interfere with blood analysis but could slightly increasepotassium values in urine when a maxi-mum acid load is excreted. Unlike flame-photometric values, increasing protein concentrations did not influence the Nova-i values. Whole blood and plasma gave virtually identical values. In plasma, the Nova-i gave slightly lower values for sodium (0.8 mmol/L) and potassium (0.0i6 mmol/L) than the Orion SS/30. Likethe OrionSSI3O, the Nova-i gave higher values than flame photometry for both sodium (3.9 mmol/L) and potassium (0.07 mmol/L). Urine samples showed good agreement between the Nova-i, operated in the urine mode, and flame photometry for sodium and for potassium if samples with electrolyte val-ues higher than 50 mmol/L were analyzed after dilution with de-ionized water. Evidently, the Nova-i is precise, capable of accurately measuring sodium and potassium in whole blood, plasma, or urine (with the above restric-tions), and should be more accurate, as is the Orion SS/30, than flame photometry for assaying specimens with above-normal protein or lipid values. AdditionalKeyphrases: ion-selective electrodes- electro-lytes #{149} intermethod comparison- flame photometry Orion SS / 30 The development of the glass sodium electrode (1, 2) and the neutral carrier (valinomycin) potassium electrode (3) has permitted the potentiometric analysis of sodium and potas-sium in biological fluids. Many types of instruments availabl