Solid-Phase Extraction Procedure of Polar Benzene- and Naphthalenesulfonates in Industrial Effluents Followed by Unequivocal Determination with Ion-Pair Chromatography/Electrospray-Mass Spectrometry

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Abstract
Highly water soluble benzene- and naphthalenesulfonates are widely used in the chemical, pharmaceutical, tannery, paper, and textile industries. In this work, Isolute ENV+ polystyrene divinylbenzene sorbent was used for the enrichment of 14 benzene- and naphthalenesulfonates from industrial wastewaters. The elution step was performed by adding 1 mL of water containing ion-pair reagent (5 mM of triethylamine (TEA) and 5 mM of acetic acid at pH 6.5) and 9 mL of methanol at 1 mL/min. The most relevant contribution was the use of ion-pair liquid chromatography followed by an orthogonal electrospray interface coupled to mass spectrometry in the negative ionization mode with postcolumn addition at 0.2 mL/min of methanol in combination with a volatile substance (triethylamine) as an ion-pair reagent. [M−H]- ion was the base peak using low fragmentor voltages of 80 V with the electrospray interface. Significant fragmentation of the quasimolecular [M−H]- ion occurs at high fragmentor voltage, producing [M−SO2H]-, [M−SO3H]-, and [SO3]•- as diagnostic ions. Collision-induced dissociation of the parent ions for the benzene- and naphthalenesulfonates studied gave the [SO3]•- fragment ion common to sulfonated compounds. At high fragmentor voltages of 150 V, [M−SO3H]- ion is more abundant and therefore has a larger peak than the [M−H]- peaks for 1,5-naphthalenedisulfonate, 2,6-naphthalenedisulfonate, 1-hydroxy-3,6-naphthalenedisulfonate, 2-hydroxy-3,6-naphthalenedisulfonate, and 2-amino-1,5-naphthalenedisulfonate. Recoveries were higher than 70%, with relative standard deviations between 1.3 and 10.7% with the exception of two naphthalenesulfonate compounds that had recoveries between 26 and 41%. Limits of detection (signal-to-noise ratio, 3) ranging from 0.6 pg to 0.13 ng (0.03−6.48 μg/L) were achieved when 150 mL of groundwater was processed. The aromatic sulfonates 3-nitrobenzenesulfonate, 4-methylbenzenesulfonate, 4-chlorobenzenesulfonate, 1-hydroxy-4-naphthalenosulfonate, 1-amino-6-naphthalenosulfonate, 1-amino-7-naphthalenosulfonate, and 1-naphthalenesulfonate and the linear alkyl benzenesulfonates C10-LAS and C11-LAS were unequivocally identified and quantitatively determined in μg/L, in wastewater samples from wastewater treatment plants and textile and tannery industries. 2-Naphthalenesulfonate was found as a major pollutant at mg/L concentration levels.

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