Magnetomotive ionic liquids

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The potential of ionic liquids (ILs) in the microextraction context is beyond any doubt. ILs, especially those that are liquid at room temperature (RTILs), present a negligible vapour pressure (attractive in HS-SDME), tuneable solubility in water (interesting in in-situ solvent formation technique) and they may be tailored to extract target analytes by the proper selection of the forming ions. RTIL have been extensively used in DLLME for these reasons, its recovery after extraction, being usually developed by centrifugation thanks to their higher density than water. However, this centrifugation step is time-consuming and several alternatives like in-syringe DLLME have been proposed to avoid it.

Magnetic materials present a clear advantage over other materials in dispersive procedures as they can be recovered from the bulk solution using an external magnet. The combination of magnetic materials/ionic liquids has been studied from different approaches. For example, ILs can be used to cover the outer surface of magnetic particles (MPs). In the easiest way, ILs can be retained on the surface by electrostatic interactions. However, the preparation of such combination requires long IL-MNPs interaction times and the IL can be easily detached from the surface of the MPs (due to pH changes or solubilization in organic solvents) and therefore it may be present in the final eluate, which is not recommendable. This issue can be solved by the covalent binding of the IL to the MPs although this approach requires a multistep synthetic procedure.

There is another issue to consider when you use a NP as support. The size of the particle defines the superficial area and therefore, the efficiency of the IL interaction with the analyte. The lower the particle size, the higher the area and therefore, the use of magnetic nanoparticles (MNPs) is preferred over micrometric ones. But, where is the limit of the particle size? The answer is clear (and obvious). The lower limit is to avoid the use of MNPs (reducing the particle size to zero). I accept that this answer is contradictory and generates another question. How can we confer magnetic properties to an IL without a MNPs?. Magnetic ILs are the response to this question. Journal of Chromatography A has already published an article where a magnetomotive room temperature dicationic ionic liquid is synthesized and applied as solvent in DLLME (1). The IL, whose formula is presented in Figure 1, is prepared in two steps and presents magnetic properties due to the FeCl4-. Although the approach is very interesting, the IL exhibits a low solubility in water that limits its dispersability into the sample.

 Our colleagues have used the IL to extract Ag and Au ions from waters and ore samples after their complexation. The analytes are finally analyzed by ETAAS with LODs lower than 7.3 ng/L.

We recommend this article to our readers. In the original manuscript, you will find the synthetic protocol, the characterization of the solvent as well as the practical application.

Reference
(1) Magnetomotive room temperature dicationic ionic liquid: A new concept toward centrifuge-less dispersive liquid–liquid microextraction. Link to the article

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