Abdel Aziz Wahbi, Ekram Hassan, Magda Barary, Essam Khamis, Dalia Hamdi.
Derivative Spectrophotometry in the visible region using absorbance versus log wavelength or wave number determination of Cyanocobalamin in injection solutions.
Pak J Pharm Sci Jan ;20(2):93-9.

Two approaches have been adopted to increase the steepness of the slopes and the sharpness of the curvature of an absorption curve in the visible region. These are recording (i) A (1cm) versus log wavelength or (ii) A (1cm) versus wavenumber. The computer program was tested by calculating the ratios of the first derivative optima for a Gaussian band, and proved that changing wavelength into log wavelength or wavenumber is effective to squeeze an absorption curve non-linearly. Spectrophotometric identification of cyanocobalamin in the visible region was carried out using the ratios (delta D1/D2) calculated for lambda, log lambda and v scales. The ratios were highly reproducible and independent of concentration. First, second and fourth- order derivative determination of cyanocobalamin in injection solutions was performed in the visible region at 20040.08, 17452.01, (20040.08 - 17452.01) cm-1 for D11(v), D12(v) delta D1 (D11 -D12) (v), respectively, and at 18018.02 cm-1 for D2(v) and D4(v).

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