Direct-Measurement Ion-Selective Electrodes:Analytical Error in

Using two commercialdirect ion-selective-electrode sodium and potassium analyzers, we found lower sodium values in cases of hyponatremia as compared with those by flame emisson spectrophotometry or indirect ion-selective-elec-trodeanalyzers.Itisshown thatthese errors can be eliminat-ed by modifyingthe calibrant, and that there is a requirement for internationally agreed-upon reference standards for use by manufacturers and laboratory personnel to assess analyti-cal performance of these analyzers. The introduction of ion-selective electrode (ISE) analyzers for direct measurement of sodium and potassium in clinical chemistry has produced a dilemma for the clinical chemist. With the traditional technique of flame photometry, results for these analytes were expressed in terms of substance concentration, whereas direct ISE technology actually mea