A novel strategy based on in-syringe dispersive liquid-liquid microextraction for the determination of nickel in chocolate samples.

In this work, a novel approach was developed to perform dispersive liquid-liquid microextraction using a rapid pressure variation to disperse the extraction solvent in an aqueous medium. A glass syringe was used to produce an environment subject to a rapid pressure difference. The element used as a model was nickel and the approach was called pressure variation in-syringe dispersive liquid-liquid microextraction (PV-IS-DLLME). The extraction solvent used was 1-butyl-3-methylimidazolium hexafluorophosphate, and ammonium pyrrolidine dithiocarbamate was the complexing reagent. The variables pH, solvent volume, amount of complexing agent, extraction time and syringe volume were studied by a factorial 2 fractional design. All variables were significant. However, the two least significant, amount of complexing agent (50.0 μL) and syringe volume (20.0 mL) were fixed at their optimum levels, according to the generated Pareto chart. A Doehlert matrix was studied for the variables volume of solvent, pH and extraction time to obtain optimal levels of these factors, and the contour plots showed the following critical values: 120.0 μL, 2.0 and 60.0 s respectively. The developed method presented limits of detection and quantification of 0.1 and 0.3 mg kg, an enrichment factor of 17 and a precision of 4.8% (100.0 μg L). The developed method was applied to the analysis of samples of powdered chocolate and certified reference material.