Trace determination of phenols in natural waters - Extraction by a new graphitized carbon black cartridge followed by liquid chromatography and re-analysis after phenol derivatization

Based upon solid-phase extraction, a sensitive, selective and robust liquid chromatography (LC) procedure for determining the U.S. EPA eleven priority pollutant phenols in natural waters is presented. The method involves passing 4 and 11, respectively, of drinking and river waters through a reversible cartridge filled with 0.5 g of a new example of graphitized carbon black (Carbograph 4) at flow-rates of about 100 ml/min. After washings, phenols are eluted by reversing the cartridge and back-flushing it with 6 ml of a CH2Cl2-CH3OH mixture containing tetrabutylammonium chloride, 10 mmol/l. The eluate is then divided in two equal portions that are taken to dryness. After reconstituting the residue of one portion of the extract with a suitable solution, phenols are separated and quantified by ion-suppression, reversed-phase LC with UV detection. The goal of analyzing phenols with a low probability of false positives can be easily reached by converting phenols in the second portion of the extract to acetyl derivatives. The reaction mixture is then injected into the same analytical column and confirmation of the eventual presence of certain phenols in the sample is obtained by observing the disappearance of the peaks for phenols and the simultaneous appearance of peaks for the corresponding acetyl derivatives. By this method, the presence of 1.3 mu g/l of 2-chlorophenol in a surface water sample was ascertained. Recovery of phenols, including phenol itself, were higher than 90%. Conversion of phenols to acetyl derivatives was completed by reacting 40 mu 1 of acetic anhydride for 6 min at 50 degrees C, except for 4,6-dinitro-2-methylphenol (78% reaction yield).