Abstract: An automatic sequential injection analysis (SIA) set-up for the determination of phenolic compounds (2-, 3- and 4-nitrophenol) in waters was designed and evaluated. The system performs an on-line phenol extraction from an aqueous medium to an organic solvent, which enables the analyte isolation and pre-concentration. The extracted phenols are on-line back-extracted into a small volume of NaOH solution and conducted to a spectrophotometric detector for quantitative analysis. This methodology is based on the formation of a thin organic solvent layer adhered to the PTFE surface of the extraction coil. In the present work, no reversed-flow was carried out in both the extraction and back-extraction steps. By using a photodiode-array detector, multilinear regression algorithms and first derivative spectroscopic techniques were evaluated in order to perform multicomponent determinations of phenol mixtures. Concentrations within the range 0.4-4.6 mg L-1 of 2-nitrophenol, 0.6-11.2 mg L-1 of 3-nitrophenol and 55.6-938 mg L-1 of 4-nitrophenol have been determined and simultaneously analyzed at a frequency of four samples per hour. A RSD of 2.2% was obtained for 2.6 mg L-1 of 2-nitrophenol, 2.3% for 5.3 mg L-1 of 3-nitrophenol and 2.2% for 330.8 µg L-1 of 4-nitrophenol, with pre-concentration factors comprised between seven and nine.

Abstract: 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-chloroburane in 1-octanol (66/34, v/v) as organic phase, a sample throughput of 11 analyzes per hour can be obtained. The detection limits for 2-, 3- and 4-nitrophenol are 0.11, 0.46 and 0.07 muM, respectively, and the relative standard deviations are less than 4%.