I recently downloaded PHREEQC and am trying to come to terms with it (this is a chore in and of itself for me). At present I am attempting to utilize PHREEQC to investigate the reduction of Fe3+ and its various complexes by dihydroanathraquinone-2,6 disulfonate (AH2DS), which is the reduced form of anthraquinone-2,6-disulfonate (AQDS). We are following the oxidation of AH2DS to AQDS using a stopped-flow apparatus with UV/Vis detection. This is being done over a range of pH and Fe3+ concentrations.
The half-cell reduction of AQDS to AH2DS follows as: AQDS + 2e- + 2H+ = AH2DS E0 = 0.253 V
I was hoping to utilize PHREEQC first model the equilibrium solution composition of a solution initially containing Fe3+, NaClO4, and AH2DS - a very simple system. After multiple attempts of building an input file that identifies ClO4-, the FeClO42+ complex, AH2DS, and AQDS. I still can't get it to converge. The output appears not to recognize the AH2DS [in the attached output file this species is designated as A(2)]. Two questions: 1) is this a problem that PHREEQC can handle, and 2) if it should be able to do this problem, what am I missing?
I very much appreciate your help in this matter.
Cal Ainsworth, Ph.D.
Environmental dynamics and Simulations, MSIN K3-61
Pacific Northwest National Laboratory
P.O. Box 999
Richland, WA 99352
Phone: (509) 375-2670
Fax: (509) 375-6954
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