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Mobile Phase Effects in Reversed-Phase and Hydrophilic Interaction Liquid Chromatography
Published in Nelu Grinberg, Peter W. Carr, Advances in Chromatography Volume 57, 2020
The retention and resolution on even the most efficient LC column results from the interactions between the solute, the stationary phase and the mobile phase, the cocktail of which characterizes different LC separation modes. Non-polar interactions are the predominant (but not the only) forces controlling the separation mechanism in reversed-phase (RP) systems employing low-polarity columns and polar aqueous-organic mobile phases. In contemporary HPLC, most frequently used are the reversed-phase separation systems. However, many polar compounds elute too early in RP LC. Hydrophilic interaction liquid chromatography (HILIC) is becoming increasingly popular, as it often provides significant improvement in the retention and separation efficiency for the separation of polar and weakly ionic compounds [1]. HILIC is essentially a normal-phase (NP) mode employing a polar column, like classical adsorption chromatography with a mixed organic solvent mobile phase. However, HILIC employs an aqueous-organic mobile phase with a high concentration of the organic solvent; it is therefore also known as aqueous normal-phase (ANP) liquid chromatography. There are a plethora of polar columns suitable for HILIC separations, including silica gel, bare or with various bonded polar ligands, and polar organic polymers [2], showing different properties such as chromatographic selectivity and water adsorption [3]. The adsorbed water forms a part of a HILIC stationary phase, and therefore the appropriate convention defining the volumes of the stationary and mobile phases is especially important for the quantitative description of retention.
Supercritical Fluid Chromatography Instrumentation
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Thomas L. Chester, J. David Pinkston
The ability to tolerate water in an SFC system creates the possibility of a HILIC retention mechanism [77, 78]. In conventional HILIC, water is used in rather small concentrations in a miscible mobile phase; acetonitrile is the usual mobile phase main component in conventional HILIC. In operation, a surface excess of water is formed on a polar stationary phase. (The surface excess is not a separate phase but is continuous with the mobile phase.) The excess water functions as a dynamic component of the stationary phase, and the composition and thickness of the surface excess layer are controlled primarily by the water concentration in the mobile phase. HILIC is possible in SFC as well if conditions create a surface excess of water on the stationary phase. At present, there have been only a few reports, and none of these have addressed kinetics. However, this is an extremely promising possibility for high-speed separations of polar solutes that are soluble in water and either acetonitrile or another SFC modifier.
LC-MS-Based Screening and Targeted Profiling Methods for Environmental Analysis
Published in Leo M. L. Nollet, Dimitra A. Lambropoulou, Chromatographic Analysis of the Environment, 2017
Kasprzyk-Hordern Barbara, Petrie Bruce
Hydrophilic interaction chromatography (HILIC) is a mode of separating polar chemicals with conventional normal-phase silica-based polar stationary phases and mobile phases similar to reversed-phase chromatography (i.e., water and an organic solvent). Mobile phase conditions can be a gradient (similar to reversed-phase mode) with a higher starting percentage of the organic solvent or as an isocratic mixture (van Nuijs et al., 2009, 2010) (Table 2.1). This mode of separation is beneficial for very polar chemicals that elute very early or show no retention during reversed-phase chromatography. To demonstrate, the antidiabetic metformin has high polarity and shows no retention by conventional reversed-phase chromatography. However, HILIC has shown to retain and suitably separate this chemical (van Nuijs et al., 2010). Therefore, HILIC is a valuable complimentary method to reversed-phase chromatography. Furthermore, elution with a higher percentage of organic solvent during HILIC chromatography also results in greater ionization efficiencies and, consequently, sensitivity during MS detection (van Nuijs et al., 2011). Fontanals et al. (2011) and van Nuijs et al. (2009, 2010) successfully applied HILIC chromatography to determine drugs of abuse and pharmaceuticals and their metabolites in environmental matrices. van Nuijs et al. (2009) developed a method for the determination of five drugs of abuse and four metabolites in influent sewage. As previously discussed, the measurement of metabolites is necessary for fate evaluation. Their determination is also essential for the sewage epidemiology approach. The presence of metabolites in environmental matrices can indicate consumption of the corresponding parent chemical, whereas their absence indicates direct disposal (Baker et al., 2012). The hydrophilic nature of metabolites (which aids their excretion in urine) makes them ideal candidates for analysis by HILIC, illustrating its value for the analysis of environmental pollutants.
A comprehensive screening shows that ergothioneine is the most abundant antioxidant in the wild macrofungus Phylloporia ribis Ryvarden
Published in Journal of Environmental Science and Health, Part C, 2018
Hengqiang Zhao, Minmin Zhang, Qian Liu, Xiaoli Wang, Ruixuan Zhao, Yanling Geng, Tityee Wong, Shengbo Li, Xiao Wang
Chromatographical separation is a standard procedure to analyze the antioxidant components in plant extracts. The separated components are then tested for their ability to scavenge certain stable free-radical dyes (such as DPPH• or 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid).24 Most studies use the reverse phase (RP)-HPLC to separate different components from the extracts.9,25–27 However, polar compounds do not separate well by RP-HPLC. Hydrophilic Interaction Liquid Chromatography (HILIC) is an alternative approach to separate small polar compounds on a polar stationary phase.28–30 A setup employing both HILIC and RP-chromatography techniques should allow the discovery of a broader spectrum of natural products. In this communication, we demonstrate the use of HILIC and RP-HPLC systems to separate the polar and non-polar antioxidants, respectively, from P. ribis. We also used an Electrospray Ionization and Quadrupole Time-Of-Flight-Mass Spectrometry (ESI-Q-TOF/MS) to identify the structures of these antioxidants.
Hydrophilic and hydrophobic materials and their applications
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2018
Darem Ahmad, Inge van den Boogaert, Jeremey Miller, Roy Presswell, Hussam Jouhara
Sample pre-treatment is a fundamental and essential step in almost all chemical analytical techniques, especially for the analysis of biological and environmental samples with complex matrix. The development of hydrophilic interaction liquid chromatography (HILIC) in the separation of polar compounds, hydrophilic materials have been extensively implemented in sample pre-treatment in various disciplines, such as pharmaceutical, clinical, toxicological, food, and environmental analysis (Tang et al. 2017).
Analysis of the behaviour of confined molecules using 2 H T 1 nuclear magnetic relaxation dispersion
Published in Molecular Physics, 2020
Adel Shamshir, Tobias Sparrman, Per-Olof Westlund
The translational and reorientation diffusion of solvent molecules are generally perturbed in different ways near solid surfaces and in confined spaces: typically, the single molecule reorientation correlation time increases and translational diffusion is hampered. These effects are due to interactions with the solid surface, which is comparatively inflexible in its response to the liquid phase. This may be important for understanding the mechanisms governing molecular separation in hydrophilic interaction chromatography (HILIC) [1]. Aqueous acetonitrile solutions are commonly used as the mobile liquid phase in HILIC, so to better understand why different analytes exhibit different HILIC retention times, we investigated the interaction between acetonitrile (which has a large dipole moment of 3.92D) and various silica surfaces with different pore sizes. In nuclear magnetic relaxation dispersion (NMRD) experiments, one measures the frequency dependence of spin-lattice relaxation rates, which can yield valuable dynamic and structural information on molecular properties at silica surfaces. In the strong narrowing regime, the NMR-relaxation times and can be expressed in terms of a spectral density function that contains information about micro-structures and relevant molecular dynamics [2]. To obtain molecular structural and dynamic information, however, the frequency dependence of the spectral density function must be determined. That is, the relaxation times must be measured over a wide range of magnetic field strengths. NMRD involves using fast-field-cycling techniques to conduct such measurements [3]. For instance, using commercial relaxometer Stelar FFC 2000 the spin-lattice relaxation time () is measured over an almost continuous range of magnetic field strengths between 0.0002 and around 1 Tesla. When applied to silica pore systems, the field dependence of the relaxation time of acetonitrile may reveal slow processes characterised by correlation times which are the inverse of the Larmor frequency. Deuterium (D) is a quadrupole nucleus with spin I = 1 for which the spin relaxation is dominated by the quadrupole interaction. For confined in silica pores the field dependence of provides information about single molecular reorientation motions or residence lifetimes at the silica surface. These results give a new view of what is the molecular mechanism behind the retention time in HILIC and an overview of previous work on this subject is given in Appendix 2.