In-situ Formation of Deep Eutectic Solvent Based Dispersive Liquid-Liquid Microextraction for the extraction of Cr(VI) from Water Samples before Its Determination by UV-Vis Spectrophotometry

• In situ formation based DES-DLLME method • Extraction and preconcentration of Cr(VI) after chelating with DPC • Determination of Cr(VI) levels in various water samples • Analysis of Cr(VI) chelated with DPC by UV-Vis spectrometry • Validation of analytical performance characteristics In this study, an in-situ deep eutectic solvent-based dispersive liquid–liquid microextraction ( in-situ DES-DLLME) method was developed for the extraction and preconcentration of Cr(VI) from water samples prior to its determination using UV–Vis spectrophotometry. Under acidic conditions, Cr(VI) ions were first complexed with 1,5-diphenylcarbazide (DPC) before extraction; the effects of key experimental parameters, including solution pH, temperature, amounts of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), DPC solution volume, and salt concentration, were systematically investigated and optimized. Under optimal conditions, the method exhibited a linear response for Cr(VI) concentrations ranging from 5 to 2000 µg/L, with a coefficient of determination (R²) of 0.995. The limits of detection (LOD) and quantification (LOQ) were 1.3 µg/L and 4.5 µg/L, respectively. An enrichment factor (FF) of 11.30 was achieved, significantly enhancing the detection sensitivity of Cr(VI) in water samples. The intra- and inter-day precisions, evaluated at two concentration levels (0.5 and 1.5 mg/L), showed relative standard deviation (RSD) values of 5.5% or lower. The percent recovery (%R), determined by spiking known Cr(VI) concentrations into river, spring, and tap water samples, ranged from 80% to 110%, demonstrating satisfactory accuracy. Overall, the proposed in-situ DES-DLLME method is simple, sensitive, eco-friendly, and precise, making it a reliable approach for the extraction and preconcentration of Cr(VI) from water and other related matrices.