DETERMINATION OF TRACE AMOUNTS OF SODIUM AND POTASSIUM IN HIGH-PURITYTANTALUM BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

A graphite-furnace atomic absorption spectrometry was applied to the d etermination of trace amounts of sodium and potassium in high-purity t antalum. A tantalum sample was dissolved in a mixture of hydrofluoric acid and nitric acid; the solution was then diluted to a given volume with distilled water. After an aliquot (20 mul) was injected into a gr aphite tube of the graphite-furnace atomizer, the absorbance of sodium and that of potassium were respectively measured under the optimum co nditions. Synthetic calibration solutions were prepared using stock st andard solutions. Since sodium and potassium form their fluorides (NaF , KF) in the presence of an excess of fluorine, the correlations betwe en the molecular absorption of NaF and KF and the ashing temperatures were investigated. Ammonium hydroxide was found to be effective as a m atrix modifier in the determination of potassium. The relative standar d deviation values of the proposed method were within 3% for 0.25 ppm of sodium and within 4% for 0.14 ppm of potassium in tantalum. The lim its of detection (3sigma of the blank values) were 1.0 pg for sodium a nd 1.2 pg for potassium, which were respectively equivalent to 0.005 p pm of sodium and 0.006 ppm of potassium in a 0.50 g sample.