[Comparison of ion-selective electrodes and flame photometry for the determination of serum Na+ and K+ for clinical purposes (author's transl)].

The ORION SPACE-STAT (SS-30) and the TECHNICON STAT/ION were used to investigate quality control of Na+- and K+-determinations in test sera (n=8) and in the plasma of 100 patients. The flame photometer IL 543 was used as a reference apparatus. The ion-selective electrode instruments, SS-30 and STAT/ION, gave results very similar to those of flame photometry. The values from the SS-30 were higher by an average of 3% to 5% compared with the values from the other instruments. An explanation for this bias may be the fact that the SS-30 (unlike the STAT/ION and the IL 543) measures electrolyte activities or concentrations in undiluted plasma water. On the basis of these results the routine use of ion-selective electrodes for Na+- and K+-determination can be recommended for clinical laboratories.