A simple, sensitive and reliable HPLC-FLD method for the routine determination of 4-nonylphenol, 4-NP and 4-tert-octylphenol, 4-tOP content in water samples was developed. The method consists in a liquid–liquid extraction of the target analytes with dichloromethane at pH 3.0– 3.5 followed by the HPLC-FLD analysis of the organic extract using a Zorbax Eclipse XDB C8 column, isocratic elution with a mixed solvent acetonitrile/water 65:35, at a flow rate of 1.0 mL/min and applying a column temperature of 40◦C. The method was validated and then applied with good results for the determination of 4-NP and 4-t-OP in Ialomita River water samples collected each month during 2006. The concentration levels of 4-NP and 4-t-OP vary between 0.08–0.17 μg/L with higher values of 0.24–0.37 μg/L in the summer months for 4-NP, and frequently <0.05 μg/L but also between 0.06–0.09 μg/L with higher values of 0.12–0.16 μg/L in July and August for 4-tOP and were strongly influenced by seasonal and anthropic factors. The method was also applied on samples collected over 2 years 2007 and 2008 from urban wastewaters discharged into sewage or directly into the rivers by economic agents located in 30 Romanian towns. Good results were obtained when the method was used for analysis of effluents discharged into surface waters by 16 municipal wastewater treatment plants, during the year 2008.

4-tert-octylphenol and 4-nonylphenol are two major metabolites of alkylphenol polyethoxylates which are widely used in different industrial and commercial applications as non-ionic surfactants. In order to ensure the ecological security by controlling the concentrations of these pollutants in water it was developed a gas chromatographic method after extraction with dichloromethane at pH = 3.5. The estimation of the performance characteristics of the method was performed by a collaborative interlaboratory study. Each participant laboratory has analysed a set of five water samples with 4-tert-octylphenol and 4-nonylphenol in different levels of concentration. The results obtained after the statistic processing of the experimental data showed that the standard deviations of repeatability and reproducibility are lying in the normal domains for a chromatographic method. Consequently, the proposed method can be used by any environmental laboratory which performs the control of the level of pollution with these two compounds.