Development of transparent film having functions of separation and sensing

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A new, highly sensitive and simple method for trace metal ions has been developed, based on the ion-pair adsorption on the surface of polyvinylchloride (PVC) film plasticized with dioctylphthalate (DOP), which serves as a water immiscible second phase. Aluminum(III) and iron(III) ions were determined at ppb level by the use of 2,2'-dihydroxyazobenzene (DHAB or H@>D22@>D2L) and crystal violet (CV^+). In addition to the large molar absorptivity of the cationic dye, CV^+, the enrichment of the blue violet ion-pair species, CV^+[M^<III>L_2]^-, onto the trancs-parent film has enabled the simple but highly sensitive determination. In the case of aluminum, the three primary colors combination system, yellow reagent (H_2L), red complex ([AlL_2]^-), and blue violet counter cation (CV^+), gave clear indication for four concentration ranges (ppb-- ppm) of aluminum. The delicate color changes (khaki-- reddish brown-- blue violet-- colorless) are well explained by the relative concentration of the reagent, H_2L, and aluminum. While, in the case of iron, the complementary color system consisting of yellow (H_2L and [FeL_2]^-) and blue violet (CV^+) brought about a different coloration system (yellow-- olive green-- blue violet). This system has been successively applied to the determination of aluminum in water samples and iron in human serum. No preparatory procedures for the separation of serum protein are required, since this method is essentially free from interferences from macromolecules and particulate matters in sample solutions. Further, the application of this method for the preconcentration step prior to HPLC analysis enabled the determination of aluminum at ppt level.