The Analysis of Potassium in Concentrated Sodium Solutions by Flame Atomic Absorption

Hanan Avraham, NRCN, Beer Sheva, Israel
Dana Revivo, NRCN, Beer Sheva, Israel
Meir Cohen, NRCN, Beer Sheva, Israel
Yair Amar, NRCN, Beer Sheva, Israel

Flame atomic absorption is a simple and fast technique to measure alkaline metals in solutions. The solution is aspirated into the flame, evaporates and is atomized. The atomized analyte is irradiated by the instrument light source at specific wavelength and the measured absorbance is proportional to the analyte concentration.

Ionization of the analyte in the flame may result in a lower signal, since the ion cannot be excited by the light source. This interference can be eliminated by adding an easily ionized element in excess, producing a large number of free electrons in the flame, reducing analyte ionization.

Cesium is a common ionization suppressant for atomic absorption. A concentration of 5 to 15mM of cesium was shown to suppress the ionization interference that occurs in the presence of sodium and potassium. Sodium and potassium can be found at brines and sea water at high concentrations. The analysis of potassium in these solutions is challenging due to the high ionization interference from sodium in the matrix.

The effect of cesium concentration on the absorbance of potassium in solutions with different concentraions was examined. In solutions with sodium:potassium ratio of 10000 the potassium signal was fully quenched when no cesium is added. The addition of 0.2% cesium (15mM) gave the maximum absorbance values, even though a ca. 10% decrease in potassium absorbance still occurred.

A calibration curve based on the potassium standard solution with 0.2% cesium was constructed. The linearity of the analysis was confirmed in the range 0.05 to 1 mg/lit, with relative uncertainty of 10%. The validity of the technique was demonstrated in both sea water and brines.