The standard addition—logarithmic extrapolation technique has been successfully applied to flame spectrometric analyses. The use of this method makes possible the determination of trace metals in samples without extensive calibration or in standards which have undefined matrices. The mathematical theory of the method has been extended to allow the calculation of the optimum addition sizes and the magnitude of the extrapolation errors. Normally three additions which are equal to, twice, and four times the original amount are optimum. Under these conditions the relative error caused by extrapolation is approximately seven times the relative error in the original intensity measurements. Thus, if the errors in the intensity measurements are ±0.5%, the error in the analysis will be of the order of 4% The utility of the method has been demonstrated in the difficult determination of calcium in the presence of phosphate and the determination of calcium and sodium in a highly viscous organic liquid.
T. E. Beukelman and S. S. Lord, "The Standard Addition Technique in Flame Spectrometry," Appl. Spectrosc. 14, 12-17 (1960)