UV‐visible and ESR spectroelectrochemical study of xylenol orange

Abstract

The proposed first step in the electroreduction of xylenol orange (XO), a reversible electrode process coupled with a chemical reaction, is based on ultraviolet (UV)-visible spectroelectrochemistry. Electrochemical excitation-electron spin resonance (ESR) in situ measurements are used to observe the radical signal produced by the first step reduction of XO. The ESR spectra of the radical in solution at pH 4.0, 4.5, and 5.0 have the same characteristics: no observed hyperfine structure, a line width of 10.5 G, and a g value of 2.0034. The structure of the XO radical and its disproportionation reaction are elucidated. l7tTRODUCTIONMany organic dyes are widely used in electroanalytical chemistry [ 11. Some electroinactive metals can be determined indirectly by forming complexes with electroactive organic dyes c l so;The electrode process of XO at a mercury electrode was investigated by Veber and Csanyi 171. It was proposed that XO undergoes two electron-transfer steps, with step 1 being nearly reversible and followed by a chemical reduction and step 2 being strongly irreversible. The first I To whom correspondence should be addressed step is, in fact, more important for most electroanalytical applications. No additional information is available on the first electroreduction step (especially on the structure of the XO radical and the nature of the following chemical reaction). Spectroelectrochemical investigations dealing with basic triphenylmethane dyes have rarely been reported. This article explores the electrode process of XO by using in situ ultraviolet (W)-visible and electron spin resonance (ESR) spectroelectrochemical methods as well as cyclic voltammetry. EXPERIMENTAL InstrumentationAn electron spin resonance spectrometer (Japan, JES-FE-3AX, x band, 100 kHz modulation, TJhI microwave resonance cavity) was combined with an FA-1 model voltammeter made by our laboratory for carrying out the in situ ESK spectroelectrochemical measurements. The IN-visible spectroelectrochemical equipment consisted o f a DMS-90 UV-visible spectropliotometer (Varian Instrument Co., Palo Alto, a) and a 1'MC nlodel 173 potentiostat. Both the ESK-electrocheniicaI cell and the gold minigrid optically transparent thin-layer cell were described previously [ 8, 91. All potentials were measured against an Ag/AgCI (saturated KCI solution) reference electrode. The experiments were performed ;it 20°C. ReagentsAnalytical grade xylenol orange was used without further purification. Other chemicals were also of analytical grade. All of the solutions were prepared with twice-distilled water. The test solutions were purged with pure 0 1989 VCH Publishers, Inc

Sm2−xDyxZr2O7 Pyrochlores: Probing Order−Disorder Dynamics and Multifunctionality

“…As can be The UV-visible spectra of the xylenol orange dye solution shows absorbance peaks at 275 and 430 nm in agreement with that reported in the literature. 55 Interestingly, when catalysts (Sm 2-x Dy x Zr 2 O 7 ) are added to the dye solution, the UVvisisble spectra exhibited a new peak at 570 nm, which could be due to the electronic interaction of dye and the catalyst (Figure 11). This new peak (570 nm) was observed for all of the compositions studied.…”