A constant ratio method for spectrographic analysis by the Lundegardh flame technique

Abstract

Certain refinements are suggested for the Lundegardh flame technique applied to the spectrographic analysis of soil and plant extracts. A new method of evaluating results called the “Constant Ratio Method” is described, in which cobalt is used as an internal standard and a series of dilutions of the unknown is used. An internal standard line is selected with an intensity similar to that of the analysis line, and an intensity ratio curve is plotted for the unknown, from which the dilution required to give an intensity ratio of one is found. Standard solutions are used to find the concentration of the element which is required to give that ratio, and from this figure the concentration of the element in the unknown is calculated. In support of the principle on which the method is based, it is shown that there is a correlation between the coefficient of variation and the amount by which the intensity ratio differs from one. Further refinements consist in the control of the acetylene supply by means of a flowmeter and the introduction of a condensing lens and concave reflector into the optical system. The Standard Deviation of the method for Na and K is estimated to be 1.5%. This figure is based upon the variance within replicates carried on separate plates and it is contended that this is the only fair method of estimating spectrographic errors.