The voltammetry of the aqueous two-electron reduction of the phenothiazine dye methylene green, known to be passivating at platinum electrodes, is reported under simultaneous activation with each of the following techniques: thermal activation in the temperature range 15-80 °C, pulsed microwave activation with a modified 800 W, 2.45 GHz domestic microwave oven, 10 Hz pulsed laser activation with a Nd:YAG laser at 532 nm, sonication, or ultrasonic activation where a 20 kHz ultrasonic horn probe is employed to generate an aqueous/ organic solvent emulsion. The relative merits of the five methodologies are compared and discussed in terms of surface activation and cleaning, mass-transport enhancement, and reduction mechanism elucidation. Comparisons are also drawn with the voltammetry of methylene blue, a dye of the same family. This is the first full report of both the effects of microwave heating on surface redox electrochemistry and of the sonoemulsion technique.
Photoelectrochemical analysis of ascorbic acid is reported in aqueous solution at a platinum channel electrode using the dissolved phenothiazine dyes methylene blue and methylene green. This is achieved by measuring the current produced by immediate electrooxidation of the reduced form of the dyes produced during the 1:1 photoreaction between the dyes and ascorbic acid induced by visible light. This behavior is similar to that reported previously for toluidine blue, and rate constants for the photochemical reaction of 360 AE 20 mol À1 dm 3 s À1 for methylene blue and 150 AE 20 mol À1 dm 3 s À1 for methylene green are determined using simulation of the observed photocurrent as a function of¯ow rate. The light used for this determination was at 620±625 nm and came from a monochromated 1000 W xenon arc lamp. The technique is extended to the immobilization of methylene blue in a zirconium phosphate lattice, which has a layer structure. Methylene blue was chosen since it intercalates to the greatest extent as evidenced by the size of new peaks apparent in its powder X-ray pattern. The dyeaphosphate compound is mixed with graphite and mineral oil such that there is a 10:1 ratio of dyeaphosphate to graphite to produce a viable photo-electrode. It is found that the photoreaction proceeds as in solution and that a light pen (laser pointer) producing 4 mW of light of wavelength 620±670 nm is suf®cient to produce signi®cant photocurrents with ascorbic acid which permit the quantitative determination of the latter at concentrations up to 1.0 mM. Finally a prototype sensor design is described, incorporating an allin-one unit comprising the photo-electrode and light pen together. This is used to measure the amount of ascorbic acid in the commercial headache remedy Resolve. A value of 31.0 AE 1.0 mg per sachet is found, compared with 30 mgasachet determined independently.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.