Pre-concentration and determination of nickel in aqueous samples using the liquid-phase microextraction and UV-Visible spectrophotometry

In this study, pre-concentrate, extract and determination of Nickel in aqueous samples was accomplished by using classic dispersive liquid-liquid microextraction (DLLME) and air assisted dispersive liquid liquid microextraction (AA-DLLME) combined with UV-Vis spectrophotometry. Independent variables includes: the type and volume of extracting and dispersing solvent, pH, ionic strength solution and the concentration of the complexing agent (DDTP) and the dependent variable was absorption value. Optimization of the variables was carried out according to chemometrics methods in three step. To choose extracting and dispersing solvent a two-way analysis of variance (two-way ANOVA) was initially used. In the second step, screening was achieved by using fractional factorial experimental design (FFD) for other variables. Afterward, optimization was performed via central composite design (CCD) to evaluate remaining variables. The results showed that 113 μL carbon tetrachloride as the extracting solvent, 1.34 mL methanol as a dispersing solvent, pH=3, 0.1% DDTP and without adding any salt were selected as optimum conditions. Finally, validation study was organized according to the ICH guidelines. The results illustrated calibration model was Y =%0.0184X + 0.1297, R2=0.9986, linearity range was 0.01-100 mg L-1. LOD and LOQ were 3.4 and 11.6 μg L-1, respectively. Accuracy was evaluated as the repeatability and intermediate precision, which RSDs were ≤8.4% and ≤20%. The accuracy was estimated on tap water, mineral water, river water and industrial wastewater as really samples. The relative error ≤ %5 was considered in the method specificity study. The proposed method was robustness when some experimental conditions such as centrifugation time (±5 min), wavelength of measurement (±2 nm) and temperature were deliberately changed.