The analysis of alkylphenol ethoxysulphonate surfactants by high-performance liquid chromatography, liquid chromatography–electrospray ionisation–mass spectrometry and matrix-assisted laser desorption ionisation–mass spectrometry Original Research Article

Commercial nonylphenol ethoxysulphonate and octylphenol ethoxysulphonate surfactant formulations, used for enhanced oil recovery, have been analysed by high-performance liquid chromatography (LC), liquid chromatography–electrospray ionisation–mass spectrometry (LC–ESI–MS) and matrix-assisted laser desorption ionisation–mass spectrometry (MALDI–MS). Mixed-mode C18/SAX and C8/SAX columns were used for both liquid chromatography and liquid chromatography–mass spectrometry analyses. Matrix-assisted laser desorption ionisation–mass spectra were obtained using either α-cyano-4-hydroxycinnamic acid or 2,5-dihydroxybenzoic acid as matrix with the addition of lithium chloride to simplify the mass spectra obtained. Data obtained from each method indicate that the nonylphenol ethoxysulphonate formulation has an ethoxymer (EO) chain length ranging from 2 to 13 EO units with an average of 6.26. This is in broad agreement with earlier studies, although the range was reported as 2–15. However, the data obtained suggest that the octylphenol ethoxysulphonate formulation has an ethoxymer chain length ranging from 1 to 8 EO units with an average chain length of 3.67. This is in contrast to earlier studies carried out by LC only, which suggested that the chain length ranged from 2 to 6 EO units with an average of 3.6. A method for the extraction of alkylphenol ethoxysulphonates from sea water using graphitised carbon black solid-phase extraction cartridges has also been developed.