Removal of pesticides from wastewater by ion pair Centrifugal Partition Extraction using betaine-derived ionic liquids as extractants

The extraction of pesticides from aqueous solutions using new ionic liquids (ILs) derived from glycine betaine as extractants was investigated. These ILs incorporate cationic esters of trimethyl(2-alkoxy-2-oxoethyl) ammonium (GBOCn+) associated with inorganic ClO4− or BF4− anions. First, batch extraction experiments were performed by using the liquid-liquid biphasic system IL/ethyl acetate/water (1:1:1; v/v) for four commonly used pesticides: 4-chlorophenoxyacetic acid (4-CPA), 2,4-dichlorophenoxyacetic acid (2,4-D), 2-[(4-methyl-5-oxo-3-propoxy-1,2,4-triazolin-1-yl)carbamidosulfonyl]benzoic acid methyl ester sodium salt (propoxycarbazone) and 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-5-methoxymethyl nicotinic acid (imazamox). Then, the liquid-liquid extraction unit operation was intensified by transposing the system into a Centrifugal Partition Extraction (CPE) device, using ethyl acetate/n-butanol/water (1:4:5; v/v) as biphasic solvent system and potassium iodide, sodium iodide or sodium perchlorate as potential displacers. The use of a lab-scale CPE column with a capacity of 300 mL allowed the intensification of the extraction procedure. The extraction and back-extraction of individual or mixture of pesticides were studied, with a particular focus on the potential separation of individual pesticides and on the recyclability of the CPE method. In optimal CPE conditions, a quantitative extraction for three of the four pesticides was obtained, with recovery percentages of 95.6%, 98.7%, 99.0%, and 100.0% for imazamox, propoxycarbazone, 2,4-D, and 4-CPA, respectively. After the back-extraction step, separated pesticides were recovered in fresh aqueous mobile phase. The recyclability studies showed that the extraction/back-extraction process can be performed at least four times while maintaining a quantitative extraction.