Preconcentration and simultaneous spectrophotometric determination of copper and mercury by dispersive liquid–liquid microextraction and orthogonal signal correction–partial least squares

A new method for spectrophotometric simultaneous determination of copper and mercury was developed by the dispersive liquid–liquid microextraction (DLLME) preconcentration and orthogonal signal correction–partial least squares (OSC–PLS). In the proposed method, dithizone was used as a chelating agent, and carbon tetrachloride and acetonitrile were selected as extraction and dispersive solvents. All factors affecting the sensitivity were optimized by the Box–Behnken design and the linear dynamic range for determination of copper and mercury was found. Under the optimum conditions, the calibration graphs were linear in the range of 10.0–250.0 and 10–300 ng mL−1 with detection limit of 2.6 and 2.8 ng mL−1 (3δB/m) and the enrichment factor of this method for copper and mercury, reached 180 and 175, respectively. The simultaneous determination of copper and mercury by using spectrophotometric methods is a difficult problem, due to the spectral interferences. The PLS modeling was used for the multivariate calibration of the spectrophotometric data. The OSC was used for preprocessing of data matrices and the prediction results of model, with and without using OSC, were statistically compared. The experimental calibration matrix was designed by measuring the absorbance over the range of 400–700 nm for 25 samples. The root mean squares error of prediction for copper and mercury with and without OSC was 0.010, 0.026 and 0.055, 0.086, respectively. The proposed method was successfully applied for the simultaneous determination of copper and mercury in spiked water and synthesis samples.