Universal screening method for the determination of US Environmental Protection Agency phenols at the lower ng l−1 level in water samples by on-line solid-phase extraction–high-performance liquid chromatography–atmospheric pressure chemical ionization mas

The applicability of a previously optimized method for the analysis of the US Environmental Protection Agency (EPA) regulations phenols, based on on-line solid-phase extraction coupled to liquid chromatography with mass spectrometric (MS) detection in different matrix loaded water samples is demonstrated. The comprehensive optimization of the mobile phase conditions and their influence on the ionization process in atmospheric pressure ionization is described in detail. In particular, MS detection of the weakly acidic phenols such as phenol, monochlorinated phenols and methylated phenols requires the absence of acidic mobile phase modifiers and buffers. Thus lower retention times and slight peak broadening of the more acidic dinitrophenols are obtained if the entire range of EPA phenols is analyzed within a single chromatographic run. The figures of merit for the method were determined and the applicability to real water samples was investigated. Limits of detection for phenols ranging from 40 to 280 ng l−1 and relative standard deviations below 8% in SCAN mode are obtained for all phenols if only 10-ml river water samples with low dissolved organic carbon (DOC 5 mg C l−1) concentrations are preconcentrated. The method was used to detect 2-nitrophenol and 4-nitrophenol in river water samples in the lower ng l−1 range. The analysis of highly matrix-loaded samples (DOC 210 mg C l−1) requires a reduced enrichment volume resulting in decreased sensitivity. Still the method is capable of reaching excellent detection limits which demonstrates its excellent suitability for screening analysis.