Stability of sulfonated derivatives of benzene and naphthalene on disposable solid-phase extraction pre-columns and in an aqueous matrix

The stability of 14 sulfonated benzene and naphthalene compounds was investigated using polymeric solid-phase extraction cartridges, based on the styrene-divinylbenzene polymer Isolute ENV+. Several different storage conditions were tested to carry out the stability study in polymeric cartridges, which included storage at room temperature, at 4 degrees C and at -20 degrees C, during a period of up to 3 months. An additional stability study was carried out, not with the polymeric solid matrix, but in an aqueous matrix. This study was performed storing the samples at 4 degrees C, during 2 months under three different conditions: acidifying the water sample to pH 2.5-3 with sulfuric acid, adding 1% of formaldehyde (additive used in waste water analyses), and storing the water sample at 4 degrees C without any additives. The extraction of the SPE process is analyzed by ion-pair chromatography-electrospray mass spectrometry, in the negative ion mode. This study showed that the stability of polar aromatic sulfonic acids on disposable polymeric cartridges and in the water matrix is related to temperature and pH, respectively. Target aromatic sulfonated compounds stored in polymeric solid-phase extraction cartridges, are more stable at lower temperatures. The target analytes showed also good stability when stored in water at acidic pH. From the different analytes studied, substituted naphthalenesulfonates suffered more degradation than mononaphthalenesulfonates or benzenesulfonates under the experimental conditions of this work. (C) 2000 Elsevier Science B.V. All rights reserved.