The estimation of lanthanum by air-acetylene atomic absorption spectrophotometry using an indirect procedure

A method for measuring the release of lanthanum from some ceramic dental ma terials was required using air-acetylene atomic absorption spectrophotometr y (AA-AAS), and an analytical procedure was devised based on the release of calcium in the presence of phosphate by lanthanum addition. The extent of phosphate interference in the determination of calcium by AA-AAS was assess ed, and it was shown that the absorbance of a 10 ppm Ca standard was reduce d by 45% in the presence of 20 ppm or more of phosphate (as PO4). Analysis of standards containing 10 ppm Ca, 20 ppm PO4, and lanthanum added at conce ntrations up to 100 ppm showed rapid increase of calcium absorbances from 1 0 to 40 ppm La, after which absorbance increased slowly to a constant value at 90 ppm La. This corresponded to the value of a 10 ppm Ca standard solut ion containing no phosphate. Closer examination of solutions containing 10- 40 ppm La revealed a quantitative relationship between lanthanum levels and calcium absorbances which deviated slightly from Beer's law. Consequent an alysis of solutions containing various amounts of lanthanum in the presence of 10 ppm Ca and 20 ppm PO4 followed by repeated analysis of standards dem onstrated good precision and reproducibility. The relative standard deviati on for repeated standard analyses was 4.2%, and the detection limit was 0.6 ppm La representing an increase of sensitivity of approximately 100 times over lanthanum determinations using nitrous oxide-acetylene techniques. The method indicates that similar procedures may be used to estimate elements which exercise similar release effects.