Deep eutectic solvent-based dispersive liquid-liquid micro-extraction for extraction of malachite green and crystal violet in water samples prior their determination using high performance liquid chromatography

A new dispersive liquid-liquid micro-extraction (DLLME) was developed to extract malachite green (MG) and crystal violet (CV) in water samples using a hydrophobic deep eutectic solvent (DES) before their determination by high performance liquid chromatography (HPLC). The hydrophobic DES was prepared by mixing benzyltriethylammonium chloride (BTEAC) as acceptor of hydrogen bond and thymol as donor of hydrogen bond at 70oC for 10 min. Influencing factors on DLLME were considered and optimised. In optimal conditions, the limit of detection (LOD) for MG and CV was 0.03 and 0.05 mu g L-1, respectively. Calibration curve for both dyes was linear in the range 0.2-500 mu g L-1 with a correlation coefficient greater than 0.99. Also, pre-concentration factor for MG and CV was 95 and 100, respectively. The within-day and between-day precision at concentration levels of 10 and 100 mu g L-1 were less than 7%. Finally, the applicability of the proposed method was evaluated through the analysis of water samples and the relative recoveries obtained (90.0-97.5%) were acceptable.