✍ Scribed by E.K. Paleologos; D.L. Giokas; S.M. Tzouwara-Karayanni; M.I. Karayannis
No coin nor oath required. For personal study only.
A methodology utilizing the cloud point phenomenon for the determination of free and tannin-bound iron in wines is presented. The method employs precipitation of the tannins and other phenolic and insoluble compounds in the micelles of a non-ionic surfactant mixture (TX-100 and TX-45) upon increase of the solution temperature, which are subsequently separated from the initial solution by centrifugation. The surfactant-rich-phase containing the tannins and the insoluble iron fraction is directly aspirated into the nebulizer of a flame atomic absorption spectrometer after its uptake with a methanolic solution of HNO 3 . The supernatant is submitted to the same cloud point extraction procedure for the determination of free iron species in the presence of a chelating agent, ammonium pyrrolidine dithiocarbamate (APDC), in order to form water-insoluble complexes with free iron. The complexes are extracted in the micelles and directly analyzed after they are diluted in a methanolic solution as described above. The total content of iron was also determined by conventional methods for comparison, yielding satisfactory results.
The calibration graph was rectilinear up to 0.35 mg l -1 Fe, with detection limits of 0.02 mg l -1 with a relative standard deviation of 2.4%. The method was successfully applied to red and white wines.
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