Optimization of an analytical method for the spectrophotometric determination of copper in tea and water samples after ultrasonic assisted cloud point extraction using a benzothiazole fluorescein derivative complexing agent

In this work, 2 ',7 '-di(2-benzothiazolyp-fluorescein (BTF) was synthesized by using 2-(2 ',4 '-dihydroxyphenypbenzothiazole (BT) and phthalic anhydride. BTF is colorful and its absorption maximum occurs at 559 nm. Interestingly, the introduction of Cu2+ affords a dramatic decrease of the absorbance at 559 nm, which is due to the spirolactonization of BTF induced by Cu2t. BTF shows high selectivity toward Cu2+ over other common metal ions in real samples, such as K+, Mg2+, Ca2+, Nat, Fe3+, Cd2+, Al3+, Co2+, Cr3+, Mn2+, Ni2+ La3+ and Zn2+. On this basis, a cloud point extraction (CPE) was developed for copper determination by a UV-vis method. The BTF-Cu2+ complex was explored for pre-concentration, and dissolved in a micellar phase composed by octylphenoxypolyethoxyethanol (Triton X-114). Under optimal experimental conditions, the decrease of the absorbance value (AA) at 559 nm is linear with Cu2+ concentration in the range from 0.03 to 2 jimol L-1 (1.90-127 mu g L-1) with a limit of detection of 7.48 nmol L-1 (3 sigma). The method has been successfully applied for the determination of copper in tea and water samples.