Dual wetting-film multi-syringe flow injection analysis extraction: Application to the simultaneous determination of nitrophenols

A dual wetting-film extraction/back-extraction system based on a multi-syringe flow injection analysis (MSFIA) set-up coupled to additional burettes and solenoid valves is proposed. The system performs on-line analyte extraction from an aqueous medium to an organic solvent based on the differential flow velocities of the aqueous and organic phases into PTFE tubing, which is due to the formation of a thin and pseudo-stationary organic film adhered to the inner walls of the extraction coil. The pre-concentrated analytes are eluted into a small eluting solution segment and conducted to a diode-array spectrophotometer for analysis. The peak maximum spectrum is used for the simultaneous determination of different analytes by using multi-component analysis with multi-linear regression (MLR). This dual system is applied to the multi-component determination of 2-, 3- and 4-nitrophenol. By using 8 ml of sample and 88 μl of 1-chlorobutane in 1-octanol (66/34, v/v) as organic phase, a sample throughput of 11 analyses per hour can be obtained. The detection limits for 2-, 3- and 4-nitrophenol are 0.11, 0.46 and 0.07 μM, respectively, and the relative standard deviations are less than 4%.