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Int. J. Electrochem. Sci., Vol. 14, 2019 5375 aliquot was taken to prepare the working solution, having a 33 M curcumin concentration, along with those of NaOH and HCl at various concentrations to set the pH adequately. 2.2.1 Acquisition of the absorption spectra. All absorption spectra were recorded aided by a spectrometer Lambda 20 UV Vis fitted with 1 cm optical path quartz cells. The spectra acquisition interval was 200 to 700 nm at 1960 nm min−1 rate. 2.3 pH measurement. A sensION potentiometer (HACH Sension+ PH31) fitted with a Ag / AgCl (KCl, 3 M) refillable, double union with silver ion barrier glass electrode (Sension+ + CAT, 5014T, (high performance); the pH range was from 0 to 14, from -10 to 100 oC, which allowed measurements of the pH up to three significant figures. 2.4 Stability study. The curcumin working solution absorbance was monitored as a function of time at three different pH values: 3.576 ± 0.001, 7.025 ± 0.001 and 10.526 ± 0.001 under experimental conditions termed “without control” and “controlled”, the latter to prevent ambient light impinging on the solutions, after N2(g) bubbling for 5 min, also keeping a gas shroud over the dissolution surface throughout the duration of the experiment while imposing a constant temperature, T = (21.0 ± 0.1) °C. 2.4.1 Electrochemical measurements Cyclic voltammetry experiments were conducted, at different times, in each of the curcumin aqueous solutions having different pH values using a typical three-electrode electrochemical cell where the working electrode was a carbon paste electrode, CPE, (see Ramírez-Silva et al. [22, 23]), the reference and the counter electrodes were: Ag /AgCl [KCl, 3 M], BAS MF-2052, and a platinum wire, BAS MW-1032, respectively, both from BASi. The working electrode potential was controlled with a potentiostat/galvanostat Epsilon-Basi coupled to a computer running the software Basic Plus for the experiment control and data acquisition. 2.5 Determination of the acidity constants. The software known as SQUAD [24] was used for the estimation of the curcumin acidity constants through analysis of the curcumin UV Vis absorption spectra as a function of pH in aqueous media.PDF Image | Curcumin in Aqueous Media at Different pH
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