Evaluation and Optimization of an On-Line Admicelle-Based Extraction-Liquid Chromatography Approach for the Analysis of Ionic Organic Compounds

Abstract

Admicelles-based solid-phase extraction (SPE) was on-line coupled with liquid chromatography/electrospray ionization/ion trap mass spectrometry, and it was proposed for the extraction of ionic organic compounds based on the formation of surfactant-analyte ion pairs. The approach was illustrated by studying the preconcentration of quaternary ammonium herbicides (quats) on sodium dodecyl sulfate (SDS) admicelles produced on alumina. Optimization of the parameters affecting SPE were studied on the basis that admicelles are dynamic entities in equilibrium with the aqueous phase. Some general guidelines could be established for method development from the results obtained. Factors influencing on-line operation were elucidated. On-line regeneration of the sorbent in each run was easily achieved by disruption of SDS admicelles with methanol and posterior coating of the alumina with SDS. The recovery of quats from drinking water samples were found quantitative for paraquat, diquat, and difenzoquat and above to 70% for chlormequat and mepiquat. Concentration factors of about 250, using sample volumes of 50 mL, were achieved. The detection limits ranged from 10 to 30 ng/L. The approach developed permits compliance with the directives of the European Community for drinking waters (100 ng/L) and goes deeply into the basis of solid-phase extractions that use surfactant-coated mineral oxide as sorbents.

Analysis of phthalates via HPLC-UV in environmental water samples after concentration by solid-phase extraction using ionic liquid mixed hemimicelles

“…06. 008 environmental matrices [9,[18][19][20]. The sorbents used are produced by adsorbing ionic surfactants (such as sodium dodecyl sulfate or cetyltrimethylammonium bromide) on the metal oxides (such as alumina or silica) surface.…”

Different Approaches for Paraquat Quantification in Waters

“…In particular, hydrochloric acid has been used as eluent in SPE pre-concentration procedures for PQ in waters [25,26,29] . Methanol (MeOH) was tested because it is sometimes applied in some eluents to desorb PQ from a wide range of SPE sorbents: silica [25][26][27][28][29][30][31] , graphitized carbon black [33] , resin [34] , alumina [35] . On the other hand, MeOH has lower boiling point than water and so, the pre-concentration step of the final extract by solvent evaporation is facilitated.…”

Analysis of Surfactants in Environmental Samples by Chromatographic Techniques

“…Thus, the hydrophilic-lipophilic copolymer Oasis HLB has been presented by Lara-Martín and co-workers [40] as an alternative for the simultaneous isolation of LAS, NPEOs, their carboxylated metabolites (SPCs and NPECs), and AEOs and their polar degradation intermediates (PEGs) from liquid samples in one single purification step. On the other hand, research on the isolation of cationic surfactants using SPE from water samples [94][95][96][97] and sediment extracts [72] is more limited. Nonpolar silica sorbents (e.g., C18) are not suitable for QACs because the strong interaction of these compounds with the silanol groups results in very broad elution bands [98].…”

“…Nonpolar silica sorbents (e.g., C18) are not suitable for QACs because the strong interaction of these compounds with the silanol groups results in very broad elution bands [98]. This issue has been partially solved employing neutral polymeric sorbents instead [72,96], although better results are obtained using sodium dodecyl sulphate (SDS) hemimicelles attached to alumina or anion exchange resins [94,95,97]. Despite this, LLE is still considered to be more effective than SPE for extraction of cationic surfactants from liquid samples [27].…”

“…Reverse-phase columns, mainly RP-18 [47,96,106] and RP-8 [52,95], are often employed for chromatographic separations of anionic, non-ionic, cationic surfactants and their degradation products. Mobile phases are solvent mixtures containing deionized water, acetonitrile and/or methanol.…”