Geopolymers as a New Class of High pH Stable Supports with Different Chromatographic Selectivity

One-pot synthesis of pillar[5]quinone-amine polymer coated silica as stationary phase for high-performance liquid chromatography

To expand the application of pillararene in chromatographic separation, we designed and fabricated a pillar[5]quinone-amine polymer coated silica through quinone-amine reaction by facile one-pot synthesis method, which was applied as a stationary phase for high-performance liquid chromatography. Separation of hydrophobic compounds, hydrophilic compounds, halogenated aromatic compounds, and 11 aromatic positional isomers was achieved successfully in this stationary phase. Reverse-phase separation mode and hydrophilic-interaction separation mode were proved to exist, indicating the potential application of the mix-mode stationary phase. Studies of chromatographic retention behavior and molecular simulation showed that multiple interactions might play an important role in the separation process, including hydrophobic interaction, hydrogen-bonding interaction, aromatic π-π interaction, electron donor-acceptor interaction, and host-guest interaction. Column repeatability and stability were tested, which showed relative standard deviations of retention time less than 0.2% for continuous 11 injections, and the durability relative standard deviations of retention time were less than 0.91% after 90 days. This novel design strategy would broaden the application of pillararene-based covalent organic polymer in chromatography and separation science.

Zinc (Ⅱ) functionalized magnetic geopolymer as sorbents for rapid extraction of Fluoroquinolones in food prior to quantification by UHPLC-MS/MS

A novel Zn@MGeo sorbent was easily constructed and can bind with FQs through the synergistic effect of electrostatic interaction and coordination. With the Zn@MGeo as sorbent, a MSPE-UHPLC-MS/MS method was established for simultaneous detection of FQs in complex matrices. The whole extraction process could be completed using 6.0 mg sorbent within 10 min under the optimal conditions. The established quantitative method obtained a wide linear range (0.01-200 μg/kg, R² > 0.9987), high sensitivity (LODs: 0.005-0.05 μg/kg) and negligible matrix effect. The method was applied for analysis of real samples, with recoveries between 75.6% and 103.7%. In addition, the sorbent could be reused at least 9 times without reducing the adsorption performance. In general, the established method not only proposes a novel sorbent for FQs extraction, but also provides a powerful tool for rapid and sensitive detection of FQs in food matrices with practical application value.

Further Evaluation of the Base Stability of Hydrophilic Interaction Chromatography Columns Packed with Silica or Ethylene-Bridged Hybrid Particles

One of the fundamental attributes of a liquid chromatography column is its stability when exposed to acidic and basic mobile phases. However, there have been relatively few reports to date on the stability of hydrophilic interaction chromatography (HILIC) columns. Here, we report the results of stability evaluations carried out for HILIC columns packed with ethylene-bridged hybrid or silica particles using accelerated conditions, employing a 100% aqueous pH 11.3 ammonium bicarbonate mobile phase at 70 °C. Under these conditions, the primary mode of column failure was a loss of efficiency due to the formation of voids resulting from the hydrolysis of the particles. We investigated the dependence of stability on the surface area of both unbonded and sulfobetaine-bonded ethylene-bridged hybrid stationary phases. The results show a clear trend of stability increasing as the surface area decreases. Several commercially available HILIC columns that are recommended for use with high-pH mobile phases were also evaluated. The results show times to 50% loss of the initial efficiency ranging from 0.3 to 9.9 h. Columns containing unbonded, sulfobetaine-bonded or diol-bonded ethylene-bridged hybrid stationary phases had longer lifetimes than amino-bonded silica or sulfobetaine-bonded, hybrid-coated, superficially porous silica columns.

Evaluation of the Base Stability of Hydrophilic Interaction Chromatography Columns Packed with Silica or Ethylene-Bridged Hybrid Particles

Stability as a function of mobile phase pH is an important consideration when selecting a chromatographic column. While the pH stability of reversed-phase columns is widely studied, there are relatively few reports of the stability of hydrophilic interaction chromatography (HILIC) columns. We evaluated the stability of silica and ethylene-bridged hybrid HILIC columns when used with mobile phases containing basic buffers. The predominant mode of column degradation observed in our studies was a decrease in efficiency due to voiding, resulting from the hydrolysis of the silica particles. Associated with this were increases in tailing factors. Retention factor changes were also noted but were smaller than the efficiency losses. The dependence of the rate of efficiency decrease on the key variables of temperature, mobile phase pH and water content were studied for an unbonded silica column. The effect of the acetonitrile concentration on the pH of the mixed aqueous/acetonitrile mobile phases was also investigated. Using conditions found to cause a 50% decrease in efficiency after approximately five hours of exposure to the basic solution, we evaluated eight different commercially available HILIC columns containing silica or ethylene-bridged hybrid particles. The results show large differences between the stability of the silica and ethylene-bridged hybrid particle stationary phases, with the latter exhibiting greater stability.

Enhancing the selectivity of polar hydrophilic analytes with a low concentration of barium ions in the mobile phase using geopolymers and silica supports

Charged analytes such as organic sulfonic acids, sulfates, carboxylates, and phosphates are often analyzed by hydrophilic interaction liquid chromatography (HILIC). In many cases, these analytes do not show any selectivity and elute near the dead time using the conventional acetonitrile-ammonium acetate buffers. In this work, we introduce a powerful selectivity enhancing technique by using a trace amount of Ba²⁺ ion in the mobile phase as a general approach for HILIC with UV-Vis detection. Silica and a newly developed material called geopolymers are used as stationary phases. Geopolymers are X-ray amorphous aluminosilicate inorganic polymers with cation exchange properties. Barium exchanged geopolymers (Ba-NM-GP) are synthesized from metakaolin based geopolymer. Thorough characterization of Ba-NM-GP is reported using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer-Emmett-Teller (BET) surface area analyzer and laser diffraction particle size distribution analyzer for the determination of their shape, size, porosity, surface area and particle size distribution respectively. It is demonstrated that in the absence of Ba²⁺, baseline separations of sulfonates, carboxylates, and phosphates is not possible, whereas, in the presence of Ba²⁺ in the mobile phase, these analytes are easily separated. Barium perchlorate is suggested as an additive for it is UV transparent, and it has practically an unlimited solubility in acetonitrile.