Evaluation of dual wavelength beta-correction spectrophotometry

The principle of the new dual wavelength beta-correction spectrophotometric method, recommended by its author, H.W. Gao in cases of high reagent blank absorbance, has been discussed. Doubts have been expressed about alpha-cor rection which occurs in the formulae and the method of its determination. T he method has been used to examine spectrophotometric methods of determinat ion of Mg(II) with eriochrome black T, Ca(II) with murexide, Al(III) with e riochrome cyanine R, Cu(II) and Co(III) with pyridylazoresorcinol. The purp ose of the examination was to compare the results of determinations obtaine d by classical spectrophotometric method and beta-correction method. It has been confirmed that the application of beta-correction alone increases the sensitivity and improves the precision and the accuracy of the methods in which reagent blank absorbance is high. It has been demonstrated that it is impossible to determine the correct alpha-correction value, and the applic ation of the correction determined according to the recommendations of the author of the method may lead to serious errors in the results.