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Photoelectrochemical Determination of Ascorbic Acid Using Methylene Blue Immobilized in α‐Zirconium Phosphate
Author(s) -
Cooper J. A.,
Woodhouse K. E.,
Chippindale A. M.,
Compton R. G.
Publication year - 1999
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/(sici)1521-4109(199911)11:17<1259::aid-elan1259>3.0.co;2-b
Subject(s) - methylene blue , ascorbic acid , chemistry , aqueous solution , photochemistry , molybdenum blue , inorganic chemistry , nuclear chemistry , phosphate , photocatalysis , organic chemistry , catalysis , food science
Photoelectrochemical analysis of ascorbic acid is reported in aqueous solution at a platinum channel electrode using the dissolved pheno‐ thiazine 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±20 mol ‐1 dm 3 s –1 for methylene blue and 150±20 mol –1 dm 3 s –1 for methylene green are determined using simulation of the observed photocurrent as a function of flow 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 dye/phosphate compound is mixed with graphite and mineral oil such that there is a 10:1 ratio of dye/phosphate 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 sufficient to produce significant 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 all‐in‐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±1.0 mg per sachet is found, compared with 30 mg/sachet determined independently.