Fluorometric flow injection determination of average copper valence in yttrium system superconductor using micro-amounts of sample

Abstract

Fluorometric determinations of average Cu valence in superconductor Y-Ba-Cu-O were performed by flow injection analysis (FIA). The present FIA apparatus had triple channels for streams of (i) distilled water (carrier), (ii) 5% ascorbic acid solution (pH 2.5) and (iii) 0.25% ο-phenylenediamine solution. A sample solution was prepared by dissolving about 0.02 μg of the Y-Ba-Cu-O in 5 ml of 5% ascorbic acid solution. The sample solution (100μl) containing Cu(II) and/or Cu(III) ions was injected into the carrier (i). Cu(II) and/or Cu(III) ions oxidized ascorbic acid in the stream (ii) to dehydroascorbic acid, which reacted with ο-phenylenediamine in the stream (iii) to produce a kind of quinoxaline derivative. The fluorescence intensity of the quinoxaline derivative (λ_ex= 350 nm, λ_em=430nm) constituted the parameter for the average Cu valence, 2[Cu(III)]+ [Cu(II)]. On the other hand, the concentration of the total Cu ions, [Cu]_total, was determined by atomic absorption spectrometry. The average Cu valence, n_av, can be calculated according to the following equation: n_av=(2[Cu(III)] + [Cu(II)])/[Cu]_total+1. The results agreed well with those obtained by iodometry. In the present method, the lower limit of determination was 0.09 ppb which corresponded to 0.02μg of Y-Ba-Cu-O sample.