Ionic liquid-based dispersive liquid-liquid microextraction combined with ultra performance liquid chromatography for the determination of metal ions

A novel, strongly hydrophobic 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)tri-fluorophosphate ([HMIM][FAP]) ionic liquid (IL) was investigated as an extraction solvent for dispersive liquid-liquid microextraction (DLLME) of Cr(VI), Co(II), Cu(II) and Ni(II) chelates with ammonium pyrrolidinedithiocarbamate (APDC) and a subsequent analysis of the extracts by ultra performance liquid chromatography. Compared with other commonly used ILs containing hexafluorophosphate and bis(trifluoromethylsulfonyl)imide anions, [HMIM] [FAP] exhibited the highest extraction efficiency. Several factors influencing the DLLME performance, such as sample pH, APDC concentration, IL volume, sample volume and the effect of potential interferents were established. Under the optimized conditions, up to 78-fold enrichment factors of analytes and acceptable extraction recoveries (>80%) were obtained. The reliability of the method was evaluated by analysing two water certified reference materials. The measured concentrations were in good agreement with certified ones.