Microchip-based Cloud Point Extraction System and Its Application to Determination of p -Nitrophenol in Water Samples

Abstract

A method was developed by integrating cloud point extraction into a microchip.Complicated operations in conventional cloud point extraction process,such as mixing,heating,and centrifugation,were avoided.The system was composed of two poly( methyl methacrylate)( PMMA) plates with the microchannels sandwiched in between.The collection material was integrated in the microchip to entrap the surfactant phase,and then the entrapped surfactant phase was eluated for sequent UV-Vis spectrophotometric determinations.The analytical performances of the microchip-based cloud point extraction system were evaluated with p-nitrophenol as a model test analyte.Effects of various parameters were optimized.The optimal conditions were as follows: sample flow rate of 0.15 mL/min,sample volume of 0.5 mL,sample pH of 11.0,surfactant concentration of 1.5%,methanol-water with a volume ratio of 70 ∶ 30 as the eluent,eluent flow rate of0.14 mL/min,and eluent volume of 0.7 mL.Within the linear range of 0.25-12 mg/L,the limit of detection was determined as 0.075 mg/L.The intra-day and inter-day relative standard deviations were 2.8%and 6.4%,respectively.When applied to the determination of p-nitrophenol in environmental water samples,the recovery values were in the range of 90.8%-102.7%.