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Gottardi
Redox-iodometry: a new potentiometric method.Gottardi W, Pfleiderer J. Anal Bioanal Chem. 2005 Jul;382(5):1328-38. Epub 2005 Jun 25. Erratum in: Anal Bioanal Chem. 2005 Oct;383(4):721-2.
"A new iodometric method for quantifying aqueous solutions of iodide-oxidizing and iodine-reducing substances, as well as plain iodine/iodide solutions, is presented. It is based on the redox potential of said solutions after reaction with iodide (or iodine) of known initial concentration. Calibration of the system and calculations of unknown concentrations was performed on the basis of developed algorithms and simple GWBASIC-programs. The method is distinguished by a short analysis time (2-3 min) and a simple instrumentation consisting of pH/mV meter, platinum and reference electrodes. In general the feasible concentration range encompasses 0.1 to 10(-6) mol/L, although it goes down to 10(-8) mol/L (0.001 mg Cl2/L) for oxidants like active chlorine compounds. The calculated imprecision and inaccuracy of the method were found to be 0.4-0.9% and 0.3-0.8%, respectively, resulting in a total error of 0.5-1.2%. Based on the experiments, average imprecisions of 1.0-1.5% at c(Ox)>10(-5) M, 1.5-3% at 10(-5) to 10(-7) M, and 4-7% at <10(-7) M were found. Redox-iodometry is a simple, precise, and time-saving substitute for the more laborious and expensive iodometric titration method, which, like other well-established colorimetric procedures, is clearly outbalanced at low concentrations; this underlines the practical importance of redox-iodometry."
Control of the amount of free molecular iodine in iodine germicides.Hickey J, Panicucci R, Duan Y, Dinehart K, Murphy J, Kessler J, Gottardi W. J Pharm Pharmacol. 1997 Dec;49(12):1195-9.
“Horseradish peroxidase has been used to generate iodine compositions that comprised principally free molecular iodine. The concentration of free molecular iodine in these enzyme-based compositions ranged from 44 to 63% of the thiosulphate titratable iodine; this is substantially higher than the corresponding value for the povidone-iodine preparation betadine. The biocidal efficacy of these compositions was proportional to the concentration of free molecular iodine. Iodine compositions with relatively low total iodine concentrations but high levels of free molecular iodine (20-175 ppm) killed Staphylococcus aureus and spores of Bacillus subtilis more rapidly than betadine. The effects of normal saline and these enzyme-based iodine compositions on the rate of epidermal regeneration in superficial swine wounds were comparable. These results suggest that an effective germicide containing a high level of molecular iodine need not be irritating or toxic.”
The decrease of efficiency of povidone-iodine preparations by blood: model experiments on the reaction of iodine containing disinfectants with protein constituentsGottardi W, Koller W Proceedings, Third Conference on Progress in Chemical Disinfection, 1986.
"The reaction of blood with povidone-iodine containing preparations results in a decrease of titrable iodine (C-ox) and a significant raise of the iodide concentration. As a consequence the concentration of free iodine (I2), decreases more than C-ox, because the equilibrium of the triiodide formation, I2 + I- <=> I3-, is shifted to the right. The extent of the decrease of C-ox and I2 is not proportional to the amount of blood but decreases with the latter. Thus the reaction of a 10% povidone-iodine solution with 20% blood gave rise to a decrease of 27-40% C-ox and 35-55% I2, while in the case of 100% blood the decrease was 80-88 resp. >90%.
"Since I2 is an important parameter, which largely correlates with the rate of killing microorganisms, the action of blood (mainly at concentrations > 20%) on povidone-preparations can cause a significant loss of disinfecting power.
"The reaction with blood takes place immediately and its extent -- as well as the fast reaction rate -- depends, as can be shown by experiments with defined protein constituents, mainly on the content of protein bound sulfur, in particular of the amino acids cysteine and methionine. Histidine, thyrosine, cytosine, albumine and uracil react also reducing iodine, but much slower than do cysteine and methionine. Alanine, glycine, arginine, asparagine, lysine, guanine, adenine and cystine however did not react with iodine under the selected conditions (aqueous solution, pH7, 25o C)."
Potentiometric evaluation of the equilibrium concentrations of free and complex bound iodine in aqueous solutions of polyvinylpyrrolidone-iodine (Povidone-iodine) [article in German]Gottardi W Fresenius Z Anal Chem (1983) 314: 582-585.
"The equilibrium concentrations of I2 and I3- in aqueous povidone-iodine solutions (0.001 - 20.0 %, pH4, 25oC) have been evaluated from the redox potential and the iodide concentration as measured by the iodide electrode (HOI, OI-, H2O+I and IO-3 can be neglected under the chosen conditions). The values obtained for I-, I2, I3- and C-ox (= iodometrically titrable iodine) indicate that the amount of iodine which is complex bound to the povidone matrix consists of HI3 -- and I2 -- groups. At concentrations > 1%, it represents nearly the whole oxidation capacity, while it can be neglected below 0.01%. The concentration of the free, molecular iodine (I2) only comes to 4.5 x 10-6 m/l (1.1ppm) in the 20% solution and increases to a maximum of ~ 10-4 m/l (25.4 ppm) in the 0.1% solution. The precision of the method is discussed and the overall error of the calculated values was found to be in the range of 8 - 12%."
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