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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.
Emerging contaminants in the atmosphere: Analysis, occurrence and future challenges
Published in Critical Reviews in Environmental Science and Technology, 2019
Pedro José Barroso, Juan Luis Santos, Julia Martín, Irene Aparicio, Esteban Alonso
Regarding sample treatment procedures, many studies reported different techniques of extraction, purification and analysis for different families of EC in air, although few of them were developed for multiresidue analysis. Future methodologies should extend the spectrum of compounds that can be determined. Soxhlet and USE are still the most used techniques when dealing with EC in the air matrix. Although these techniques are now automatized, they are still long, time consuming and require large volumes of solvents. Future efforts should focus towards environmental friendliness, low cost, miniaturization, automation and simplicity. New developments such as in vivo-SPME and microdialysis have been identified as successful techniques for in situ determination of EC in crops and therefore extensible to leave matrices. Furthermore, additional research is clearly needed to fill the existing gap of a multiresidual analytical methodology for the determination of EC and their intermediate degradation products as well as enantiomeric compounds. Transformation products and chiral compounds will gain more environmental concern in the next future and to our knowledge no information have been find at this respect in the atmospheric compartment. To this end, the recourse to high resolution MS platforms (quadrupole time of flight (QqTOF), quadrupole-linear ion trap (QqLIT) and Orbitrap) has been increasing significantly, as well as the previous separation of such compounds by using chiral chromatography, hydrophilic interaction chromatography (HILIC) or two-dimensional liquid chromatography (LCxLC) systems.
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.