Spectrophotometric investigation of ascorbinate complexes of metals

It has been shown that ascorbic acid forms metal complexes of the types ML and MHL, depending on the pH used, and that the complexes are relatively unstable, especially those of type MHL. Their absorption spectra have no maxima but have a steep slope at 320-380 mmicro and are displaced to longer wavelengths relative to the absorption spectrum of ascorbic acid. A bigger shift occurs for elements of variable valency, and the spectra move to longer wave-lengths as the pH is raised; at pH 7-9 a new maximum appears at 380-420 mmicro, indicating a change of structure of the ascorbinate ion, probably with a lactone. Metals can be determined spectrophotometrically as their ascorbinates, at concentrations down to 10(-5)M for Ti, U, Os, V, Cr, Nb, Ta, Zr, Mo, W, Sn, Pb and Th, and 10(-4)M for lanthanides, Sc, Hf and Sb.