In-syringe dispersive liquid-liquid microextraction.

Dispersive liquid-liquid microextraction (DLLME) has recently been widely used in the separation and preconcentration of various chemical species. Among the various approaches using DLLME are systems that use a syringe as an extraction environment. In this review, details of some methods that use this approach are presented. The ways to promote dispersion, analytical characteristics, and the advantages and disadvantages of the methods, among other aspects, are discussed critically. Finally, some trends in the use of in-syringe microextraction systems are described.

An alkaline dissolution-based method using tetramethylammonium hydroxide for metals determination in cow milk samples.

This study approaches the development of a method for the determination of Ca, Mg, Zn, and Fe in liquid and powdered cow milk. The method is based on sample dissolution assisted by ultrasound energy in tetramethylammonium hydroxide (TMAH) media and determination by flame atomic absorption spectrometry (FAAS). Central composite design (CCD) associated with response surface methodology and desirability function allowed the fast and efficient optimization of the variables involved in the performance of the dissolution. The developed dissolution method allowed Ca, Fe, Zn, and Mg determination in milk samples with adequate analytical characteristics for these determinations. Addition/recovery tests and analysis of a certified reference material of skimmed powdered milk (ERM-BD150) have shown that this method presents enough accuracy to carry out these analyses.

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 25-1 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-1, an enrichment factor of 17 and a precision of 4.8% (100.0 µg L-1). The developed method was applied to the analysis of samples of powdered chocolate and certified reference material.