Determination of malachite green and crystal violet in environmental water using temperature-controlled ionic liquid dispersive liquid-liquid microextraction coupled with high performance liquid chromatography

Temperature-controlled ionic liquid dispersive liquid-liquid microextraction (TC-IL-DLLME) was introduced to analyze malachite green (MG) and crystal violet (CV) in environmental water by coupling with high performance liquid chromatography (HPLC). In the method, 1-octyl-3-methylimidazolium hexafluorophosphate ([C ₈MIM][PF ₆]) and methanol were selected as appropriate extraction and dispersive solvents, respectively. Target compounds were extracted into the IL phase (dispersed completely in the aqueous phase) at a proper temperature. Several other parameters that could affect extraction performance were optimized, such as IL volume, sample pH, salinity, extraction time, temperature and centrifuging velocity. Under the optimum conditions (IL volume, 80 μL; sample pH, 4; salinity, 20% sodium chloride; extraction time, 50 min; temperature, 70 °C; centrifuging velocity, 1500 rpm), the established method offered: (i) good linear range (0.25-20 μg L ^-1); (ii) low detection limits (MG, 0.086 μg L ^-1; CV, 0.030 μg L ^-1); (iii) good reproducibility (relative standard deviation, MG, 9.4%; CV, 7.6%; n = 5) and good recoveries (91.7% for MG and 97.2% for CV, respectively; n = 5); (iv) high enrichment factor (254 for MG, 276 for CV), which makes the method suitable to monitor low concentrations of MG and CV in aqueous systems.