Multicomponent sequential injection analysis determination of nitro-phenols in waters by on-line liquid-liquid extraction and preconcentration

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 preconcentration. 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 1(-1) of 2-nitrophenol, 0.6-11.2 mg 1(-1) of 3-nitrophenol and 55.6-938 mg l(-1) of 4-nitrophenol have been determined and simultaneously analysed at a frequency of four samples per hour. A R.S.D. of 2.2% was obtained for 2.6 mg 1(-1) of 2-nitrophenol, 2.3% for 5.3 mg 1(-1) of 3-nitrophenol and 2.2% for 330.8 mu g 1(-1) of 4-nitrophenol, with preconcentration factors comprised between seven and nine. (C) 2000 Elsevier Science B.V. All rights reserved.