The color reaction systems between various metal ions and o-hydroxyhydroquinonephthalein(Qnph) as a xanthene dye, in the presence of various water soluble surfactants(cationic. anionic, non-ionic surfactants) alone or in combination, were systematically investigated at various pH areas. The coexistence of cationic and non-ionic surfactants, such as Zephiramine (Zp) and Brij 35, was most effective for the color reaction systems between Qnph and gallium(III), as a metal ion, at weakly acidic media. By using the color reaction between Qnph and gallium(III) in the coexistence of Zp and Brij 35, an improved and sensitive spectrophotometric determination of gallium(III) was proposed as method 1, and the calibration curve was rectilinear in the range of 0∼7.0 μg of gallium(III) in a final solution of 10ml at pH 6.4. The apparent molar absorptivity was 1.5 × 105 1 mol-1 cm-1 at 560 nm, and the interference of foreign ions was decreased by ½∼ ¼-fold in comparison with other methods; method 3—in the presence of Zp alone at pH 6.4, method 2—in the presence of Tween or Brij 35 alone, without Zp, at pH 8. Thus, the use of Qnph as a xanthene dye and the combination of cationic and non-ionic surfactants, such as Zp and Brij 35(perhaps, on the mixed micellar media), was most effective and its color reaction was used for the separative assay of gallium(III).
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