Comparative Study of the Determination of Sodium and Potassium Ions using Ion Selective Electrode, Flame Emission Photometry and Spectrophotometric Methods

Abstract Electrolyte measurement is very crucial especially for critical patients, but there is a lot of apprehensions regarding the reporting of electrolyte owing to different methods used for electrolyte assay. This study was carried out to compare the ion selective electrode, flame emission spectrophotometry and spectrophotometric methods in the determination of serum sodium and potassium ion. A total of twenty-nine (29) samples were analyzed for sodium and potassium using ion selective electrode, flame photometer and spectrophotometer. The result showed that the mean values of sodium and potassium using spectrophotometer were 140.40±3.70 mmol/l and 4.06±0.52 mmol/l respectively, mean values of sodium and potassium using ion selective electrode were 139.57±3.45 mmol/l and 4.21±0.49 mmol/l respectively and the mean values of sodium and potassium using flame photometer were 138.60±5.18 mmol/l and 3.96±0.37 mmol/l respectively. A Passing-Bablok regression curve between ion selective electrode and spectrophotometer showed a very good correlation in measuring sodium and potassium while between the flame photometer and the other two methods showed a weak correlation. The limit of agreement of sodium plotted by Bland and Altman technique of ion selective electrode versus spectrophotometer, ion selective electrode versus flame photometer and spectrophotometer and flame photometers were -4.0 to 2.3, -12.0 to13.9 and -11.8 to 15.4 respectively while the limit of agreement of ion selective electrode versus spectrophotometer, ion selective electrode versus flame photometer and spectrophotometer and flame photometers were -0.48 to 0.17, -1.39 to 0.89 and -1.22 to 1.03 respectively. This study has shown that there is a good degree of agreement when electrolytes are measured using ion selective electrode and spectrophotometer but there is a poor limit of agreement when these two methods are compared with flame photometry. The high degree of agreement demonstrated by ion selective electrode and spectrophotometer in this work shows that the results given by these two methods do not differ enough to cause any problems in clinical practice and that they can be used interchangeably.