Ionic liquids versus ionic liquid-based surfactants in dispersive liquid–liquid microextraction for determining copper in water by flame atomic absorption spectrometry

The optimum conditions for the IL-DLLME method using C 4 MIm-PF 6 were: 100 μL of neat C 4 MIm-PF 6 , 1 mL of acetonitrile, 10 mL of water, no control of pH for environmental waters, NaCl content of 23 g L − 1 , diethyl dithiocarbamate (DDTC) as complexing agent at 10 mg L −1 and final dilution of the micro-droplet with acetonitrile up to 70 µL. The optimum conditions for the in situ IL-DLLME method using C 16 C 4 Im-Br were: 0.8 mL of acetonitrile, 10 mL of water containing C 16 C 4 Im-Br at 25.2 mmol L −1 , final dilution step of the micro-droplet with 200 µL of acetonitrile and remaining conditions as those of C 4 MIm-PF 6 .

The analytical performance of both methods was similar, being slightly better for the IL-DLLME method using C 4 MIm-PF 6 , with limits of detection (LOD) of 3.3 µg L −1 (versus 5.1 µg L −1 when using C 16 C 4 Im-Br), precision values as intraday relative standard deviation (RSD in %) lower than 8.8% (being of 10% for the C 16 C 4 Im-Br method) and an enrichment factor of 54 (being 27 when using C 16 C 4 Im-Br). The DLLME-FAAS method with C 4 MIm-PF 6 was used in the analysis of environmental waters with successful performance, with relative recoveries of 110% and 105%, and interday precision with RSD values of 21% and 7.4% for spiked levels of 60 and 160 µg L −1 , respectively.

The results obtained when analysing an urban wastewater sample coming from an inter-laboratory exercise was comparable to those obtained for other 93 laboratories. The method was also valid for the determination of Cu 2+ in presence of foreign ions commonly found in natural waters.