Analytical methods for the determination of surfactants in surface water.

WILLETTS, Matthew. (1999). Analytical methods for the determination of surfactants in surface water. Doctoral, Sheffield Hallam University (United Kingdom)..

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Abstract

The determination of surfactants in environmental surface water is required due to recent concern over possible adverse health effects that have been associated with them. This thesis is concerned with two aspects of the analysis of non-ionic and anionic surfactants in surface water.An HPLC phase-switching method has been developed in an attempt to overcome the problem of an interfering anionic species (thought to be humic acids) that masks the presence of any linear alkylbenzene sulphonate surfactants in river water samples. This problem has arisen following the development of an HPLC method for the determination of linear alkylbenzene sulphonates and alkylphenol ethoxylate surfactants in surface water in a previous research project. The phase-switching method allows the mobile phase to be diverted to either a C[1] or C[18] column or both. The linear alkylbenzene / humic acid portion was diverted to the C[18] column after elution from the C[1] column; the alkylphenol ethoxylate portion of the sample was then allowed to separate on the C[1] column as usual. Then the linear alkylbenzene / humic acid portion was separated on the C[18] column using a different mobile phase. The method works well with standards; however, with real samples it was not clear as to the identity of the peaks that may or not be linear alkylbenzene sulphonates. In addition, recent batches of the Spherisorb C[1] column were unable to adequately resolve the nonylphenol ethoxylate ethoxymers.The reason for this loss of resolution was investigated by elemental analysis and x-ray photoelectron spectroscopy. Bulk percentage carbon and surface carbon coverage both showed a similar trend. The earlier batch of Spherisorb column that produced the best resolution of nonylphenol ethoxylate ethoxymers had the lowest surface carbon coverage and the lowest percentage bulk carbon. Recent batches of the Spherisorb column along with columns from Supelco and Hypersil contained higher levels of carbon. These results suggest that resolution of the ethoxymers is due to the unreacted hydroxyl groups on the silica surface, and that the presence of the alkyl moiety actually hinders the process. In order to account for this a "pseudo reverse phase" mechanism has been invoked for this separation.The second section of this thesis involves the development of a new qualitative and quantitative method for the determination of nonylphenol ethoxylate surfactants in surface water by matrix-assisted laser desorption / ionisation time-of-flight mass spectrometry. The sample was mixed with a concentrated solution of 2,5-dihydroxybenzoic acid or alpha-cyano-4-hydroxycinnamic acid as a matrix. Approximately 1 muL of the resulting solution was added to a stainless steel target and, after evaporation of the solvent, the target was placed into the mass spectrometer. The resulting spectra showed intense [M+Na][+] and [M+K][+] adducts for each ethoxymer group. Extracted samples from the River Don analysed by this method showed a similar characteristic envelope of peaks, corresponding to sodium and potassium adducts for nonylphenol ethoxylates. For quantitative determinations Triton X-100, an octylphenol ethoxylate surfactant, was added as an internal standard. A concentrated solution of lithium chloride was also added to produce much less complicated spectra consisting of solely [M+Li][+] adducts. Good linear relationships were seen for each individual ethoxymer over the entire distribution. The method showed excellent results for spiked surface water samples, but the concentrations of nonylphenol ethoxylates in recent samples were below the current limit of detection for this method of 100 mug/L.

Item Type: Thesis (Doctoral)
Additional Information: Thesis (Ph.D.)--Sheffield Hallam University (United Kingdom), 1999.
Research Institute, Centre or Group: Sheffield Hallam Doctoral Theses
Depositing User: EPrints Services
Date Deposited: 10 Apr 2018 17:22
Last Modified: 08 Jun 2018 09:19
URI: http://shura.shu.ac.uk/id/eprint/20540

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