Hydrophobic/hydrophilic separation performance evaluation of a mixed-mode ionic liquid embedded stearyl thioglycolate functionalized silica stationary phase.

In this work, a novel imidazolium ionic liquid embedded multifunctional chromatographic stationary phase (Sil-AVI-ST) was synthesized by the radical-mediated thiol-ene click reaction. A wide range of samples including hydrophilic sulfonamides, vitamins and nucleosides/bases as well as hydrophobic phthalates, bisphenols, alkylphenols and steroid hormones were selected to evaluate the separation ability of the newly obtained Sil-AVI-ST. As expected, an efficient separation of the above tested analytes was successfully achieved in different chromatographic modes. It was proved that multiple stationary phase-analyte interaction forces promoted the selective separation. The Sil-AVI-ST column provided multiple retention mechanisms, enabling the efficient separation of diverse analytes with different polarity. More importantly, embedding a polar ligand (1-allyl-3-vinyl-imidazolium) could improve the separation efficiency of long-chain alkyl bonded stationary phases for hydrophilic analytes, and the developed Sil-AVI-ST column could also realize the detection of hydrophobic analytes under water-rich conditions, which is impossible for the conventional hydrophobic columns. Therefore, the newly prepared Sil-AVI-ST stationary phase has a good practical application potential.

Insights in column packing processes of narrow bore and capillary-scale columns: Methodologies, driving forces, and separation performance - A tutorial review.

Having fundamental insights in the properties of stationary phases and in the driving forces during the column packing process, is crucial to obtain highly efficient and robust packed-bed column technologies for use in separation science. Here we discuss the properties of the most commonly-used stationary-phases, i.e., silica particulate materials, including fully-porous and core-shell silica particles and provide an overview of the most commonly used column hardware and available frit technologies. The different packing approaches that are considered are dry packing, high-pressure slurry packing, electrokinetic packing, and packing using centrifugal forces. In particular, sedimentation of particles in slurries and particle interaction during the packing process affecting the resulting sphere packing are discussed.

Innovative preparation of ureido/dodecyl dual-functionalized silica as a versatile mixed-mode stationary phase for high-resolution chromatographic separations.

Developing a versatile stationary phase to achieve the purpose of efficiently separating various target analytes is of great significance. In this work, ureido/dodecyl dual-functionalized silica (Sil-Ur-DD) was synthesized and employed as a new mixed-mode stationary phase for high-resolution chromatographic analysis. It was observed that multiple interactions, including hydrophobic, hydrophilic, hydrogen bonding, electrostatic and π-π interactions, contributed to the retention. Nucleosides and nucleobases could be effectively determined in hydrophilic interaction chromatography mode, and the separation performance of the Sil-Ur-DD was found to be even superior to that of the commercial XAmide column. Environmental endocrine disruptors, including alkylphenols, bisphenols, steroid hormones and phthalates, were more favorably separated in reversed-phase chromatography mode with highly aqueous mobile phases compared with the commercial C18-silica column. The experimental results indicated that the combined effect of ureido and long-chain alkyl groups obviously enhanced separation efficiency and selectivity. More significantly, the proposed method concerning the preparation of an efficient separation material with powerful separation ability is economical and environmentally friendly, which provides a proven and effective way for the recycling and utilization of the discarded chromatographic packing materials, thereby showing a good application prospect.

[Preparation and application of urushiol methacrylate-bonded silica liquid chromatographic stationary phase].

A novel stationary phase for high performance liquid chromatography was prepared using urushiol methacrylate as the chromatographic ligand. The mixed urushiol methacrylate was prepared using urushiol and methacryloyl chloride via a substitution reaction and then coated onto the surface of spherical silica by physical adsorption. The spherical silica was chemically modified with 3-methacryloyloxypropyl trimethoxysilane. Then, the urushiol methacrylate-bonded silica stationary phase (USP) was synthesized via the surface radical polymerization of urushiol methacrylate and the pendant vinyl groups onto the surface of the spherical silica. The stationary phase was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and elemental analysis. The results revealed that the urushiol methacrylate was successfully immobilized on the spherical silica surface after the surface polymerization reaction, and that it had excellent monodispersity. The stationary phases were packed in a stainless-steel hollow column by the slurry packing method, with methanol as the slurry solvent and absolute ethanol as the propelling solvent. The chromatographic performance of the stationary phases were investigated for the separation of Gastrodia elata extract. Acetonitrile-0.05% phosphoric acid solution (3:97, v/v) was employed as the mobile phase at a flow rate of 0.4 mL/min, with the detection wavelength of 220 nm. The separation performance for Fructus evodia extract was also studied, using acetonitrile-water (50:50, v/v) as the mobile phase at a flow rate of 0.5 mL/min, and the detection wavelength was 290 nm. This column showed good separation performance for both these extracts. Out of the five peaks observed for the Gastrodia elata extract, one was attributed to gastrodin, but the other four peaks need to be further verified. Two peaks assignable to evodiamine and rutaecarpine were observed for the Fructus evodia extract. Compared with C18 column, the USP column allowed for more effective separation of the components from the Gastrodia elata extract, with baseline separation; on the other hand, the chromatographic conditions for the separation of the components of the Fructus evodia extract were more environmentally friendly and safer. Because of the low flow rates adopted for the separation of the Gastrodia elata and Fructus evodia extracts, the amount of mobile phase used could be reduced. This study provides not only a new method for the separation and purification of gastrodin and evodiamine in real samples, but also a new strategy for the preparation of chromatographic stationary phases. It expanded the application of raw lacquer in chromatographic separation materials.

Comparison of underivatized silica and zwitterionic sulfobetaine hydrophilic interaction liquid chromatography stationary phases for global metabolomics of human plasma.

To increase metabolome coverage in global LC-MS metabolomics, often both reversed-phase liquid chromatography (RPLC) and hydrophilic-interaction liquid chromatography (HILIC) are implemented in parallel. However, there is a lack of consensus in the literature on the best HILIC stationary phase to employ for global metabolomics of human biological fluids. The objective of this study was to compare in detail the performance of two commonly employed HILIC phases: zwitterionic sulfobetaine ZIC-HILIC stationary phase and an underivatized silica HILIC stationary phase. During method development, the effect of salt concentration in the mobile phase was also investigated, and 5 mM ammonium acetate was selected. The stationary phases were evaluated using a mixture of 37 polar standards covering a range of logP values (-10 to 3.73), molecular weights (59-776 Da), charges (15 anions, 11 cations, and 11 neutral) as well as 17 lipid standards to understand phospholipid behaviour on the two stationary phases. The criteria used for the comparison included the quality of the chromatographic peak shape, adequate analyte retention, peak separation capability, and metabolite coverage. The zwitterionic ZIC-HILIC column provided better chromatographic performance over the silica stationary phase with 14 standards achieving good quality peaks compared to the 7 with the silica column. Only 2 standards were undetected with the ZIC-HILIC column compared to the 14 undetected with the silica column. In human plasma, 1966 and 1650 metabolites were observed on the ZIC-HILIC column in positive and negative electrospray ionization (ESI) respectively. On the silica HILIC column, 1773 and 2028 metabolites were observed in positive and negative ESI respectively, showing comparable performance of the two phases. Next, the effect of adding 10 mM ammonium phosphate to the samples to improve the analyte peak shape and metabolite coverage was investigated for both ZIC-HILIC and silica HILIC. In contrast with recently reported results for pZIC-HILIC, there was no clear evidence that ammonium phosphate addition was beneficial for human plasma samples. In conclusion, ZIC-HILIC provided better chromatographic performance for polar plasma metabolomics than underivatized silica in terms of chromatographic peak shape and chromatographic resolution, while maintaining comparable metabolite coverage. The addition of ammonium phosphate to human plasma was not beneficial for either of the two stationary phases.