Pressurized liquid extraction followed by liquid chromatography-mass spectrometry for the determination of major surfactants in marine sediments

Abstract

A simple and fast method is described for the determination in marine sediments of the anionic and non-ionic surfactants most commonly used worldwide. This group of compounds includes linear alkylbenzene sulfonates (LAS), alkyl ethoxysulfates (AES), nonylphenol polyethoxylates (NPEOs) and alcohol polyethoxylates (AEOs). The proposed method involves the extraction of 5 g of dry sediment with methanol by using an accelerated solvent extraction unit (ASE), preconcentration and purification by means of an octadecyl-bonded silica (C₁₈) mini-column and analysis by high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS). The recoveries varied in the range of 51–109%, with a standard deviation between 4 and 11. Limits of detection were in the range of 1–5 µg/kg for sediment samples. This method was applied to the determination of these surfactants in a sediment core collected in the Bay of Cadiz (SW of Spain), with concentration values up to 637 µg/kg for LAS, 401 µg/kg for NPEOs, 861 µg/kg AEOs and 125 µg/kg for AES.

Keywords:

• Marine sediments
• Anionic surfactants
• Non-ionic surfactants
• Extraction methods
• Pressurized liquid extraction

Acknowledgments

We express our gratitude to Rufino Ligero (Departamento de Física Aplicada, Universidad de Cádiz) for assistance during the sampling of the sediments and to Emiliano Gómez (Servicios Centrales de Ciencia y Tecnología, Universidad de Cádiz) for his technical support with the LC/MS system. We also thank PETRESA, KAO Corp. and P&G for supplying us with the surfactants standards. This study was carried out within the I+D CICYT Project REN2001-2980-C02-01 and with the help of a Spanish Ministry for Education and Science grant.