Colorimetric determination of copper in water and food samples based on its effect on cloud point extraction of curcumin nanoparticles

Copper is an essential bio-element which is present in plants and animals but it is toxic at high concentration levels. It could be accumulated in different organs such as liver and cause health problems [1]. Therefore, its determination in environmental samples is important from analytical chemistry point of view. However direct determination of trace elements has some drawbacks because the detection limits of most analytical techniques is not enough for their determination and a sample pretreatment and preconcentration is required. In this research a cloud point extraction method using curcumin nanoparticles is reported for copper enrichment. Curcumin is a hydrophobic polyphenol compound which has been recognized as the active principle of turmeric and could be extracted from the dried root of the rhizome of Curcuma Longa. Curcumin nanoparticles are extracted into Triton X-100 as a nonionic surfactant and show an absorption band with maximum wavelength of 436 nm. When Cu(II) is present the absorbance of the surfactant rich phase is decreased. The decrease in the absorbance the presence of Cu(II) was used as an analytical signal (ΔA) for the determination of Cu(II). The influence of chemical variables such as pH of the sample solution, ionic strength, and concentration of the curcumin on the cloud point extraction was investigated. Under the optimum conditions two linear calibration curves in the range in the range of 0.5-15 and 3-45 ng mL-1 using different concentrations of curcumin nanoparticles was obtained. The detection limit was 0.39 ng mL-1 and relative standard deviation of ten replicate measurements of 25 and 40 ng mL-1 of Cu(II) was 4.6% and 1.7%, respectively. The proposed method was successfully applied to the determination of Cu(II) in water and food samples with satisfactory results.