Determination of alkylphenols in water samples using liquid chromatography–tandem mass spectrometry after pre-column derivatization with dansyl chloride

• The conditions of derivatization of alkylphenols with dansyl chloride were tested.
• Improved method provides more reproducible results and lower limits of quantitation.
• The high levels of alkylphenols in blank samples affect the result of analysis.
• Comparison of the level of alkylphenols in drinking and wastewater was carried out.

The present study describes an effect of reaction condition of pre-column derivatization of alkylphenols (APs): bisphenol A (BPA), 4-tert-octylphenol (4-t-OP), 4-octylphenol (4-OP), 4-n-nonylphenol (4-n-NP), and isomers of 4-nonylphenol (iso-NP) with 5-(dimethylamino) naphthalene-1-sulfonyl chloride (dansyl chloride, DNSC) on their LC–ESI–MS/MS determination in water samples. Chemical derivatization improves the sensitivity and selectivity of LC–MS/MS analysis. In principle, alkylphenols can be analyzed by LC–MS/MS without derivatization. However, pre-column derivatization of APs increases the sensitivity up to 1000 times in comparison with the analysis of underivatized alkylphenols. Reaction conditions affecting formation of the DNSC-derivatives, such as various solvent, reaction temperature, reaction time, DNSC concentration and pH values were tested. The most suitable conditions, in terms of achieving a high sensitivity, resulting from this study are: acetonitrile as reaction solvent, 60 min as reaction time, 60 °C as reaction temperature, pH values 10.5, 0.5 mg mL−1 as DNSC concentration. Calibration curves are linear at least in the range of 1–1000 ng mL−1, limits of detection (LOD) and limits of quantification (LOQ) ranging from 0.02 to 0.25 pg/injection and from 0.08 to 0.83 pg/injection, respectively. The improved procedure was successfully applied for the analysis of APs and BPA in real water samples. The median concentration of BPA and iso-NP obtained in bottled waters was 4.7 ng L−1 and 33.5 ng L−1, respectively. The median concentration of 4-t-OP was 1.3 ng L−1.