Preconcentration based dispersive liquid-liquid microextraction for spectrophotometric determination of zinc in natural water and human blood after multivariate optimization based on Box-Behnken design

A new simple and rapid dispersive liquid-liquid microextraction has been applied to preconcentrate trace levels of zinc as a prior step to its determination by spectrophotometric method. In the proposed method, 4- (2-pyridylazo) resorcinol (PAR) is used as a chelating agent, and chloroform and ethanol are selected as extraction and dispersive solvent. The optimization strategy is carried out by using two level full factorial designs. Results of the two level full factorial design (24) based on an analysis of variance demonstrated that the pH, concentration of PAR, amount of dispersive and extraction solvents are statistically significant. Optimal condition for three variables: pH, concentration of PAR, amount of dispersive and extraction solvents are obtained by using Box-Behnken design. Under the optimum conditions, the calibration graphs are linear in the range of 30-220 ng mL-1 with detection limit of 11.2 ng mL-1 (3δB/m) and the enrichment factor of this method for zinc reached at 130. The relative standard deviation (RSD) is 1.4% (n=7) at 50 ng mL-1 level. The method is successfully applied to the determination of trace amount of zinc in water and human blood samples.