Development of a deep eutectic solvent-based dispersive liquid–liquid microextraction coupled with spectrophotometer technique for determination of trace amount of Hg(II) in water samples

In this research, a dispersive liquid–liquid microextraction based on a deep eutectic solvent (DES-DLLME) as an easy, fast, low cost, highly sensitive and selective method was proposed to separate and pre-concentrate Hg(II) in water samples before its determination by spectrophotometer. Hg(II) was first complexed with 4,4′-bis (dimethylamino) thiobenzophenone (TMK) as a very selective chelating agent and then subjected to DES-DLLME. The proposed new DES was synthetized by mixing octanoic acid as donor of hydrogen bond and coumarin as acceptor of hydrogen bond at 60ºC for 5.0 min. The application of the new solvent (coumarin/octanoic acid) in DLLME can make the proposed method a new and relatively green sample preparation technique. The effective parameters in the complexation and microextraction steps were investigated and optimized. Under the optimum conditions, linearity was seen in the range of 1.0–100 µg L −1 with a correlation coefficient of 0.9985. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.3 and 1.0 µg L −1 , respectively. The enrichment factor was 200. The extraction efficiency for mercury was ≥ 80%, which is comparable to similar research. In addition, the applicability of the developed method was investigated by analyzing water samples including electronic industry wastewater, mineral water, tap water, well water, and seawater; satisfactory recoveries (91.8–98.0%) were obtained.