title: Liquid phase micro-extraction of linear alkylbenzene sulfonate anionic surfactants in aqueous samples.
abstract: Hollow fiber liquid phase micro-extraction (LPME) of linear alkylbenzene sulfonates (LAS) from aqueous samples was studied. Ion pair extraction of C10, C11, C12 and C13 homologues was facilitated with trihexylamine as ion-pairing agent, using di-n-hexylether as solvent for the supported liquid membrane (SLM). Effects of extraction time, acceptor buffer concentration, stirring speed, sample volume, NaCl and humic acids were studied. At 10-50 µg L-1 linear R2-coefficients were 0.99 for C10 and C11 and 0.96 for C12. RSD was typically ~15%. Three observations were especially made. Firstly, LPME for these analytes was unusually slow with maximum enrichment observed after 15-24 h (depending on sample volume). Secondly, the enrichment depended on LAS sample concentration with 35-150 times enrichment below ~150 µg L-1 and 1850-4400 times enrichment at 1 mg L-1. Thirdly, lower homologues were enriched more than higher homologues at low sample concentrations, with reversed conditions at higher concentrations. These observations may be due to the fact that LAS and the amine counter ion themselves influence the mass transfer at the water-SLM interface. The observations on LPME of LAS may aid in LPME application to other compounds with surfactant properties or in surfactant enhanced membrane extraction of other compounds.
authors: Division of Analytical Chemistry at Lund University, P.O. Box 124, Lund 221 00, Sweden. niklas.larsson@organic.lu.se.
authors: Niklas
authors: N
authors: Larsson
authors: University of Opole, Oleska 48, Opole 45-050, Poland. paulina.mizera@gmail.com.
authors: Paulina
authors: P
authors: Otrembska
authors: Department of Analytical Chemistry, Faculty of Chemistry, University of Seville, C/Professor García González s/n, Seville 41012, Spain. mvn@us.es.
authors: Mercedes
authors: M
authors: Villar
authors: Division of Analytical Chemistry at Lund University, P.O. Box 124, Lund 221 00, Sweden. jan_ake.jonsson@organic.lu.se.
authors: Jan Åke
authors: JÅ
authors: Jönsson