Redox-iodometry: a new potentiometric method

Analytical and Bioanalytical Chemistry, Oct 2005

Waldemar Gottardi, Jörg Pfleiderer

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Redox-iodometry: a new potentiometric method

Anal Bioanal Chem Redox-iodometry: a new potentiometric method Waldemar Gottardi . Jörg Pfleiderer 0 1 2 0 J. Pfleiderer Institute for Astrophysics, University of Innsbruck , 6010 Innsbruck , Austria 1 W. Gottardi ( 2 Page 1329 , Algorithm 1 3 ) Institute of Hygiene and Social Medicine, Innsbruck Medical University , 6010 Innsbruck , Austria We apologize to the reader that this paper contains a number of printing errors. The corrections are listed below according to the pages on which they occurred. Equation (15) E0 ¼ Emeas þ S log y2 x - > N Cl þ 2I þ Hþ !> N þI2 þ Cl IO3 þ 5I þ 6Hþ ! 3I2 þ 3H2O ClO2 þ 4I þ 4Hþ ! 2I2 þCl þ 2H2O ClO2 þ I ! ClO2 þ 1=2I2 I2 þ I ! I3 Equation (9) Equation (10) Calibration (Algorithm 3) The potential actually measured comprises the potential Ered of the redox reaction I2+2e−↔2I−, the potential of the reference electrode (Eref), and its liquid junction potential (Ej): Emeas ¼ Ered Ered is clearly defined, for a chosen temperature, by the Nernst equation Ered ¼ E0;I2=I where E0;I2=I ¼ 622:4mV , S=29.58 mV/decade at 25°C, and f is the activity coefficient. Eref and Ej, however, are also influenced by the concentration of the salt bridge, and they are generally not known exactly. From the expressions for the measured and calculated redox-potentials of the standardizing solution Emeas ¼ E0;I2=I Ecalc ¼ E0;I2=I it follows easily that the sum of the unknown potentials comes to Eref þ Ej ¼ Ecalc which yields the standard value where [I−] and [I2] are the equilibrium concentrations calculated with Algorithm 3 (see “Supporting Information”). Since the measurements are performed at a high, nearly constant ionic strength (see below), the activity coefficient can be waived. Calculations and graphs were done with GraphPad PRISM Version 4.00. The SD of the crucial difference ΔE=E0*−E (see constant A in “Supporting Information”, Algorithm 2) was calculated with SDΔE=(SDE0*2+SDE2)0.5. The levels of significance (t-test) were calculated with a TI-58-59 calculator fitted with Applied Statistics Modul-2. Page 1335, second to last line under a) should read Calculations [5] show that at the conditions of Procedure B at pH 6.6, the relative equilibrium concentration of HOI comes to 0.014% of the total oxidation capacity (c(Ox) ≤10−4 M), while it is <0.05% with Procedure A at pH 8.3 (c(Ox)≤0.01 M). Page 1336, last line under a) should read ... expected at pH<8.4 Legend to Fig. 3 should read Fig. 3 Calculated redox-potentials [5] of decimal dilutions of 0.01 M I2 with addition of zero(○) 0.001 (□), 0.01 (▵), and 0.1 M KI (⋄) at pH 4; dotted line indicates theoretical slope (29.58 mV/decade) Algorithm 3: The mass balances Eqs. 7 and 8 and the mass-law expressions Eq. 4–6 were transformed by the substitution to the polynomial Eq. 20 cðOxÞ; D ¼ cðI Þ D; R ¼ 1 BK3; T ¼ K3 2½DK5 þ B2K6K3 þ 1 ; K32 K52ð2D CÞ þ K5 2K6 ; and Q=BK32(4K6−K5) The root of Eq. 20 i.e. x=[I2] was found by iteration. The second equation is then easily solved. Page 1337, Supporting information Equation (19)


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Waldemar Gottardi, Jörg Pfleiderer. Redox-iodometry: a new potentiometric method, Analytical and Bioanalytical Chemistry, 2005, 721-722, DOI: 10.1007/s00216-005-0100-z