Abstract
A simple paper-based colorimetric assay for trace determination and speciation of Cu2+ in water samples has been developed. The proposed method was based upon the use of a commercial book-paper patterned with miniaturized spots of 3-(5-hydroxy-4-carboxyphenylimino)-5-fluoro indol-2(H)one (HCFI) reagent. Book-paper was characterized by scanning electron microscopy, EDAX and goniometer analysis, where the latter analysis confirmed hydrophobic character (theta similar to 114 degrees). The low wettability of the platform confined Cu2+ droplet onto the HCFI spot to form a visually distinct colored complex even at trace level (10(-3) mu g mL(-1)) concentration. The limit of detection of the proposed probe was 3-orders of magnitude lower as compared to similar assay executed on pristine filter paper. An excellent linear dynamic range (10(-2)-10(1) mu g mL(-1)) was achieved with good regression coefficient (R-2 = 0.9987). Due to high selectivity of HCFI reagent for Cu2+ the developed method showed minimum interference towards diverse ions, textile colored dyes as well as surfactants. The proposed method was also applied for speciation of trace labile and complexed fractions of Cu2+ in standard solutions and environmental water samples as well. To the best of our knowledge, this is the first time Cu2+ speciation has been demonstrated on paper-based platform in such a facile manner.