Zwitterionic hydrophilic interaction

Acronyms d SPE dispersive solid-phase extraction HILIC hydrophilic interaction liquid chromatography IT ion trap LLE liquid—liquid extraction MSPD matrix solid-phase dispersion PGC porous graphitized carbon PLE pressurized-liquid extraction PHWE pressurized hot-water extraction QqQ triple quadrupole QLIT quadrupole linear ion trap QuEChERS quick, easy, cheap, effective, rugged, and safe TCA trichloroacetic acid UHPLC ultraperformance liquid chromatography ZIC ttILIC zwitterionic hydrophilic-interaction liquid chromatography. 

R.N. Rao, RK. Maurya, R. Kuntamukkala, WD. Vitthal and Mvnk Talluri, Molecularly imprinted polymer for selective extraction of 3-methylflavone-8-carboxylic acid from human urine followed by its determination using zwitterionic hydrophilic interaction hq-uid chromatography, /. Sep. Sci., 34 (22) 3265-3271, 2011. 

Zwitterionic hydrophilic interaction chromatography (ZIC-HILIC) has also been used as a method of separating DPAA and PAO [42]. This separation technique relies on a partitioning mechanism between the mobile phase (high... 

Figure 4.11 Separation of nine different organoarsenicals including PAO (peak 1) and PAA (peak 2). (a) Isocratic separation with 78% acetonitrile and (b) gradient separation with 78-70% acetonitrile. ICP-MS and ES-IMS were used in parallel for elemental and molecular identification [42]. D. Xie, et ai, Separation of organoarsenicals by means of zwitterionic hydrophilic interaction chromatography (ZIC-HILIC) and parallel ICPMS/ESI-MS detection, Eng. Life ScL, 2008, 8, 582-588 with permission from Wiley...

Hydrophilic interaction chromatography (HB IC) or aqueous normal-phase chromatography (ANP) refers to the use of polar stationary phases (e.g., bare silica, silica, or polymeric phases with bonded zwitterionic ligands, diol phases) in combination with a mobile phase rich in organic solvent but containing a significant amount of water (typically at least 3%). Bell [97] summarized the advantages of this technique as follows ... 

Wikberg, E., Sparrman, T., Viklund, C., Jonsson, T., and Irgum, K. 2011. A nuclear magnetic resonance study of the state of water in neat sihca and zwitterionic stationary phases and its influence on the chromatographic retention characteristics in hydrophilic interaction high-performance liquid chromatography. J. Chromatogr. A 1218 6630-6638. 

One characteristic feature of surfactants is their amphiphilic nature. These molecules present two moieties the hydrophobic moiety (usually a hydrocarbon chain) interacts with the nanotube sidewalls, while the hydrophilic part, called polar head group, is generally charged or has zwitterionic character. It has the double function of helping solubility in aqueous solvents and of providing additional stabilization towards tubes aggregation by coulombic charge repulsion. 

Cetyltrimethylammonium bromide CH3(CH2)i5N(CH 3)381 is a typical cationic surfactant. Dissociation of this compound results in amphiphilic cations and small hydrophilic anions. This classification of surfactants is similar to the classification of strongly interacting compounds (other than surfactants) in Sections II and III into cations (Section II A), anions (Section II B) and electroneutral and zwitterionic organic compounds (Section III). The adsorption of anionic surfactants is indeed enhanced, when the adsorbent carries high positive surface charge (at low pH for materials hsted in Tables 3.1, and 3.3-3.5), and adsorption of cationic surfactants is more pronounced at high pH, and the adsoiption of nonionic surfactants is often rather insensitive to the pH. However, the mechanisms of surfactant adsorption, and experimentally observed adsorption isotherms of surfactants are very different from the compounds discussed in Sections II and III. 

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