Journal
JOURNAL OF CHROMATOGRAPHY A
Volume 1315, Issue -, Pages 8-14Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chroma.2013.09.041
Keywords
SPME-fibers; Cationic surfactant; Cation-exchange; pK(a); Sorption; Humic acid
Funding
- European Oleochemicals and Allied Products Group (APAG)
- European Chemical Industry Council (CEFIC) sector groups
- Environmental Risk Assessment and Management (ERASM)
- China Scholarship Council (CSC)
- Unilever [CH-2012-0078]
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A passive sampler tool (solid-phase microextraction, SPME) was optimized to measure freely dissolved concentrations (C-w,C-free) of lauryl diethanolamine (C12-DEA). C12-DEA can be protonated and act as a cationic surfactant. From the pH-dependent sorption to neutral SPME coatings (polyacrylate and PDMS), a pK(a) of 8.7 was calculated, which differs more than two units from the value of 6.4 reported elsewhere. Polyacrylate coated SPME could not adequately sample largely protonated C12-DEA in humic acid solutions of pH 6. A new hydrophobic SPME coating with cation-exchange properties (C-18/SCX) sorbed C12-DEA 100 fold stronger than polyacrylate, because it specifically sorbs protonated C12-DEA species. The C-18/SCX-SPME fiber showed linear calibration isotherms in a concentration range of <1 nM-1 mu M (well below the CMC). Using the C-18/SCX-SPME fibers, linear sorption isotherms to Aldrich humic acid at pH 6 (ionic strength 0.015 M) were measured over a broad concentration range with a sorption coefficient of 10(5.3). (C) 2013 Elsevier B.V. All rights reserved.
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