Silica Hydride Research Articles

Utility of “flip-flop” chromatography employing silica hydride stationary phases with simultaneous photodiode array ultraviolet and single quadrupole mass detection for the analysis of seized drugs

For confirmation and/or screening purposes, rapid, selective, and precise chromatographic methods are required. In this vein, the utility of SiH columns (C18, UDC Cholesterol, and Diamond Hydride) with photodiode array UV absorption and single quadrupole MS detection for multi-modal separation of representative drugs from different drug classes on a single column using the same solvent reservoirs was investigated. For a conventional two column approach employing a combination of conventional C18 and silica columns operating in both the reversed phase chromatographic and hydrophilic interaction chromatographic modes, gradient analysis is required for the first column and there is a lack of retention on the second column for non-amine analytes. In comparison, all analytes are retained for two relatively rapid (< 10 min), precise (% RSD <0.4%), and non-correlated isocratic separations (R2=0.2115) when using a UDC Cholesterol column.

Silica Hydride: A Separation Material Every Analyst Should Know About

This review describes the development, special features and applications of silica hydride-based stationary phases for HPLC. The unique surface of this material is in contrast to ordinary, standard silica, which is the material most frequently used in modern HPLC stationary phases. The standard silica surface contains mainly silanol (Si-OH) groups, while the silica hydride surface is instead composed of silicon-hydrogen groups, which is much more stable, less reactive and delivers different chromatographic and chemical characteristics. Other aspects of this material are described for each of the different bonded moieties available commercially. Some applications for each of these column types are also presented as well as a generic model for method development on silica hydride-based stationary phases.

Chromatographic characterization of a silica hydride-based amide stationary phase.

An amide phase based on a porous silica hydride support material is tested for retention characteristics in both the reversed-phase and aqueous normal-phase modes. A series of retention maps (capacity factor vs. mobile phase composition) were obtained using reference standards of varying analyte sizes, functionalities, and polarities. An assessment of the specific column selectivity is made and classes of compounds are identified that show high potential for effective retention, resolution, and efficiency when using amide functionalized silica hydride columns for reversed-phase and aqueous-normal phase separation. Several practical applications are presented that illustrate the capabilities of this particular column format.

Analysis of Advanced Glycation End products in ribose-, glucose- and lactose-crosslinked gelatin to correlate the physical changes induced by Maillard reaction in films

The Maillard reaction (MR), a condensation reaction between carbonyl-containing and free amino-containing compounds, has attracted the interest of scientists within the food industry, nutrition & health, and materials science. However, due to the complexity of the reaction much remains to be clarified regarding the nature of the reaction products and their effect on the properties of protein/saccharide-containing products. In this work, gelatin-based films with various saccharides (glucose, lactose & ribose) and thermally crosslinked (105 °C) for different times (0, 2, 6, 24 h), were analysed to deliver deeper insight into the molecular transformations induced by MR and their effect on the physical properties of films, considered as complex systems. Coloured, ultraviolet–visible (UV–Vis) light-absorbing, crosslinked, and fluorescent compounds were analysed by colourimetry, UV–Vis spectrophotometry, solubility, as well as fluorescence spectroscopy. The colour of the films turned pale yellow and dark brown, the solubility decreased, while the UV–Vis light absorption capacity of the films significantly increased as the heating time increased. Rapid and simultaneous separation of Advanced Glycation End products (AGEs) on a silica hydride column, and their detection using high resolution mass spectrometry (MS) showed an increment in high molecular weight (HMW) compounds and gelatin crosslinking, which was related to the formation of AGEs. Of these, pentosidine, vesperlysine, GOLD and MOLD were quantified, while crossline and glucosepane were also detected. More noticeable physical and molecular changes were observed as the saccharide reactivity increased, which was indirectly related to the molecular size of the added saccharides: pentoses > hexoses > disaccharides.

Dispersive liquid-liquid microextraction, an effective tool for the determination of synthetic cannabinoids in oral fluid by liquid chromatography–tandem mass spectrometry

In the present work, dispersive liquid-liquid microextraction (DLLME) was used to extract six synthetic cannabinoids (JWH-018, JWH-019, JWH-073, JWH-200, or WIN 55,225, JWH-250, and AM-694) from oral fluids. A rapid baseline separation of the analytes was achieved on a bidentate octadecyl silica hydride phase (Cogent Bidentate C18; 4.6 mm × 250 mm, 4 μm) maintained at 37 °C, by eluting in isocratic conditions (water:acetonitrile (25:75, V/V)). Detection was performed using positive electrospray ionization–tandem mass spectrometry. The parameters affecting DLLME (pH and ionic strength of the aqueous phase, type and volume of the extractant and dispersive solvent, vortex and centrifugation time) were optimized for maximizing yields. In particular, using 0.5 mL of oral fluid, acetonitrile (1 mL), was identified as the best option, both as a solvent to precipitate proteins and as a dispersing solvent in the DLLME procedure. To select an extraction solvent, a low transition temperature mixture (LTTM; composed of sesamol and chlorine chloride with a molar ratio of 1:3) and dichloromethane were compared; the latter (100 μL) was proved to be a better extractant, with recoveries ranging from 73% to 101 % by vortexing for 2 min. The method was validated according to the guidelines of Food and Drug Administration bioanalytical methods: intra-day and inter-day precisions ranged between 4 % and 18 % depending on the spike level and analyte; limits of detection spanned from 2 to 18 ng/mL; matrix-matched calibration curves were characterized by determination coefficients greater than 0.9914. Finally, the extraction procedure was compared with previous methods and with innovative techniques, presenting superior reliability, rapidity, simplicity, inexpensiveness, and efficiency.

Back Cover: Rapid and simultaneous analysis of advanced glycation end products on silica hydride column: Comparison of ultraviolet, fluorescence, and mass spectrometry detectors

DOI: 10.1002/sscp.202000077 The cover picture shows the collagen structure with several crosslinks then the isolation of the intact GOLD, MOLD and pentosidine advanced glycation end products by acid hydrolysis. The separation was then carried out on a Cogent Diamond Hydride column under isocratic conditions with a short time of 5.5 min. The eluted peaks were detected on the ultraviolet, fluorescence, and mass spectrometry detectors in which fragmentation by tandem mass spectrometry was measured. This method was then used to monitor the formation of advanced glycation end products in gelatin sample treated with glucose.

Rapid and simultaneous analysis of advanced glycation end products on silica hydride column: Comparison of ultraviolet, fluorescence, and mass spectrometry detectors

AbstractGlycation of collagen produces advanced glycation end products including pentosidine, glyoxal‐lysine dimer, and methylglyoxal‐lysine dimer. These products are markers for aging and associated with the development of several diseases. In this study, a rapid and simultaneous analytical method for pentosidine, glyoxal‐lysine dimer, and methylglyoxal‐lysine dimer was developed. The separation of advanced glycation end products was carried out on a silica hydride column using either acetonitrile or methanol in water with 0.1% (v/v) formic acid. A total run time of &lt;5.5 min was achieved using isocratic elution and 11 min using gradient conditions. The gradient elution also allowed the rapid and simultaneous of collagen crosslinks and advanced glycation end products in one run. The eluted peaks were detected by mass spectrometry then the fragmentation was measured by tandem mass spectrometry to confirm their identity. The method developed herein was successfully applied to high‐performance liquid chromatography with fluorescence and ultraviolet detection. Although the ultraviolet detection sensitivity of glyoxal‐lysine and methylglyoxal‐lysine dimers is low, it is useful for preparative work for the collection of intact advanced glycation end‐products. This method was applied to several biological sample products and used to monitor the formation of glycation product in gelatin treated with glucose.

The utility of silica hydride-based stationary phases for dual-mode ultra high performance liquid chromatography separation of synthetic cathinone positional isomers.

Emerging drugs usually mimic the effects of traditional drugs, but are not always controlled due to the chemically altered structures. Positional isomers of emerging drugs are difficult to analyze because they challenge the separation and detection techniques commonly employed by forensic laboratories. The utility of silica hydride stationary phases for the ultra-high performance liquid chromatography separation of synthetic cathinone positional isomers was studied in this manuscript. SiH phases are operable under both reversed phase and aqueous normal phase chromatographic conditions without the need to change solvent reservoirs. The separation of eight positional isomers of the synthetic cathinone, pentedrone, was investigated using five silica hydride phases, and compared to a classical dual column reversed phase, hydrophilic interaction chromatography system, and to a bimodal pentaflurophenyl column. Significant selectivity differences were observed using either a combination of a classical reversed phase C18 and NP Silica columns or the various bimodal columns. The silica hydride silica-C column, which contains no derivatized ligands attached to the silica hydride backbone, not only gave the most orthogonal separation of the bimodal columns, but provided a unique separation of all eight positional isomers (resolution ≥ 1) using the combination of reverse phase and aqueous normal phase chromatographic conditions.

Application of linear solvation energy relationships and principal component analysis methods for the prediction of the retention behaviour of E-resveratrol analogues with substituted silica hydride stationary phases

In this investigation, application of linear solvent energy relationships (LSERs) and principal component analysis (PCA) methods have been employed to investigate the structure-retention dependencies of E-resveratrol analogues separated under different stationary and mobile phase conditions. To this end, the retention of 22 analogues have been determined with phenyl, diol, bidentate anchored C18 (BDC18) and Diamond Hydride™ C18 (DHC18) substituted silica hydride stationary phases under isocratic chromatographic conditions using mobile phases containing 0.1 (% v/v) formic acid and different acetonitrile or methanol contents from 10 to 90% (v/v) in 10% increments. In general, these compounds showed decreasing retention with increased acetonitrile or methanol content in the mobile phase with all the stationary phases. The retention order generally followed their log P values, although some unique selectivity variations were apparent depending on the nature of the selected stationary and mobile phases. These 22 compounds contained different backbone functionalities linking the phenyl ring A to phenyl ring B and different numbers of hydroxyl groups in the phenyl ring A/phenyl ring B. Structure-retention descriptors, derived according to LSER concepts, were analysed by PCA methods to provide group classification of these resveratrol analogues from the associated PC1 versus PC2 score plots. These results revealed that the selectivity of these compounds was dominated by hydrophobic and steric interactions. Based on the number and position of hydroxyl groups in a specific resveratrol analogue, a reliable curve fitting approach (indicated by R2 > 0.99 for the correlation between experimental and predicted log k values) was derived for prediction of the retention of these analytes under different mobile phase isocratic separation conditions. The application of similar methods are anticipated to find general utility for the analysis of diverse classes of other low molecular mass compounds in the different modes of liquid chromatography, permitting enhanced levels of prediction and evaluation of the retention attributes of polar and non-polar compounds.

The Development of Silica Hydride Stationary Phases for High-Performance Liquid Chromatography from Conception to Commercialization

The development of a stationary phase material for high-performance liquid chromatography based on a surface of silica hydride as opposed to silanols on ordinary silica is discussed including synthetic approaches, characterization, and applications. There are several synthetic approaches available to create a silica hydride surface. Modification of the Si–H moiety on the silica surface can be accomplished through the use of a hydrosilation reaction. Both the intermediate silica hydride and the material modified with an organic moiety can be characterized by a number of spectroscopic as well as a variety of other methods. Further insights into the retention mechanism are provided through chromatographic measurements. The ultimate utility of any chromatographic stationary phase material is determined by its success in solving challenging analytical problems. A broad range of applications is reviewed to illustrate the versatility and usefulness of silica hydride-based stationary phases.

Studies on the Extraction of Several Polyphenols with Different Silica Hydride Stationary Phases

The solid-phase extraction of several polyphenolic compounds with different silica hydride-based stationary phases, as well as an unmodified type-B silica, has been investigated. In particular, the propensities of these stationary phases to extract the selected polyphenolic compounds in the batch-binding mode in the presence of 100% methanol or 50% (v/v) aqueous/methanol solvents have been examined. In addition, the zeta-potential values of these different sorbents have been determined in the same solvent compositions. The results indicated that the batch-extraction behaviour of these polyphenolic compounds with the type-B silica, unmodified silica hydride, the Diamond Hydride™ particles, silica hydride particles modified with immobilized phenyl groups or with other non-polar ligands of larger steric size, such as bidentate octyl, bidentate octadecyl, or cholesteryl groups, did not overall correlate with the particle’s zeta-potential values. However, these results indicated that the selectivity attributes in solid-phase extraction procedures of different types of silica hydride materials with polyphenolic compounds can be differentiated from experimental data acquired with small quantities of structurally related test analytes under aqueous normal-phase conditions solely from physical measurement methods, such as static batch-extraction measurements and associated GS–qMS methods of analysis.

Application of Sub-2 Micron Particle Silica Hydride Derivatized with Vancomycin for Chiral Separations by Nano-Liquid Chromatography.

1.8μm Silica hydride particles have been derivatized with vancomycin and applied to the enantioseparation of some racemic herbicides and nonsteroidal anti-inflammatory drugs (NSAIDs) by nano-liquid chromatography. The chiral stationary phase (CSP) was packed for only 11cm and the enantiomers were separated utilizing a laboratory-assembled instrumentation. The new CSP was very effective for the separation of the abovementioned acidic compounds, while poor resolutions were obtained for basic compounds. Mixtures of acetate buffer with methanol or acetonitrile allowed the chiral resolution of all compounds. Fast chiral separation of a NSAIDs-related compound can be achieved in less than 60s.

Origin of the selectivity differences of aromatic alcohols and amines of different n-alkyl chain length separated with perfluorinated C8 and bidentated C8 modified silica hydride stationary phases

Perfluorinated C8-(PerfluoroC8) and bidentate anchored C8-(BDC8)-modified silica hydride stationary phases have been employed for the isocratic separation of homologous phenylalkanols and phenylalkylamines differing in their n-alkyl chain length, using aqueous-acetonitrile (ACN) mobile phases of different ACN contents from 10 to 90% (v/v) in 10% increments. These analytes showed reversed-phase (RP) retention behaviour with mobile phases of <40% (v/v) ACN content with both stationary phases but with the BDC8 stationary phase providing longer retention. The PerfluoroC8, but not the BDC8, stationary phase also exhibited significant retention of these analytes under conditions typical of an aqueous normal phase (ANP) mode (i.e. with mobile phases of >80% (v/v) ACN content), with the analytes exhibiting overall U-shape retention dependencies on the ACN content of the mobile phase. Further, these stationary phases showed differences in their selectivity behaviour with regard to the n-alkyl chain lengths of the different analytes. These observations could not be explained in terms of pKa, log P, molecular mass or linear solvation energy concepts. However, density functional theory (DFT) simulations provided a possible explanation for the observed selectivity trends, namely differences in the molecular geometries and structural organisation of the immobilised ligands of these two stationary phases under different solvational conditions. For mobile phase conditions favouring the RP mode, these DFT simulations revealed that interactions between adjacent BDC8 ligands occur, leading to a stationary phase with a more hydrophobic surface. Moreover, under mobile phase conditions favouring retention of the analytes in an ANP mode, these interactions of the bidentate-anchored C8 ligands resulted in hindered analyte access to potential ANP binding sites on the BDC8 stationary phase surface. With the PerfluoroC8 stationary phase, the DFT simulations revealed strong repulsion of individual perfluoroC8 ligand chains, with the perfluoroC8 ligands of this stationary phase existing in a more open brush-like state (and with a less hydrophobic surface) compared to the BDC8 ligands. These DFT simulation results anticipated the chromatographic findings that the phenylalkanols and phenylalkylamines had reduced retention in the RP mode with the PerfluoroC8 stationary phase. Moreover, the more open ligand structure of the PerfluoroC8 stationary phase enabled greater accessibility of the analytes to water solvated binding sites on the stationary phase surface under mobile phase conditions favouring an ANP retention mode, leading to retention of the analytes, particularly the smaller phenylalkylamines, via hydrogen bonding and electrostatic effects.

Preparation of polar group derivative β-cyclodextrin bonded hydride silica chiral stationary phases and their chromatography separation performances

Three novel β-cyclodextrin compounds derived with piperidine which is flexible, l-proline containing a chiral center, ionic liquid with 3,5-diamino-1,2,4-triazole as the cation were designed and synthesized as chiral selectors for enantiomer separation, whose name were (mono-6-deoxy-6-(piperidine)-β-cyclodextrin, mono-6-deoxy-6-(l-proline)-β-cyclodextrin, mono-6-deoxy-6-(3,5-diamino-1,2,4-triazole)-β-cyclodextrin, multi-substituted 3,5-diamino-1,2,4-triazole-(p-toluenesulfonic)-β-cyclodextrin), respectively. In addition, to enhance the polarity of chiral stationary phases, hydrosilylation and silylation reactions were implemented to derive ordinary silica, the common used selector carrier, to hydride silica, whose surface is covered with proton. 31 pyrrolidine compounds and some chiral drugs were tested in both polar organic mobile phase mode and normal mobile phase mode. 6-Deoxy-6-l-proline-β-cyclodextrin-CSP showed satisfactory separations in polar organic mobile phase mode and exihibited a strong separation capability in different pH values; multi-substituted 3,5-diamino-1,2,4-triazole-(p-toluenesulfonic)-β-cyclodextrin-CSP can separate pyrrolidine compounds in both mobile phase modes with high resolutions and separation efficiency compared to commercially available CSPs, making it to be the most valuable object to study. The composition of mobile phase, type of stationary phase as well as the peak problem of chromatograms was discussed deeply.

Evaluation of silica hydride materials for the LC–MS analysis of cathinones and benzylpiperazines

A new LCMS approach is tested for the analysis of controlled substances using bath salts (cathinones) as a model system. Since the structure of cathinones have a polar functionality (the amine group) as well as an aromatic component, separation on the LC column could be achieved in the reversed-phase(RP) or aqueous normal phase (ANP) modes. Since silica hydride columns can function in both modes they have considerable potential for the analysis of substances that have both polar and nonpolar functionalities. Four different silica hydride-based columns (C18, phenyl, cholesterol and diol) are tested in either the RP or ANP and RP modes using representative compounds to determine their applicability to bath salt analysis. A protocol for the analysis of a related illicit drug, benzylpiperazine, is developed on another silica hydride column (Diamond Hydride) in the ANP mode. Further testing is done on physiological samples, saliva (with 78–98% recovery) and hair, in order to determine that the approach outlined in this study could be utilized for these and other controlled substances in biological matrices.

Silica hydride based phases for small molecule separations using automated liquid chromatography–mass spectrometry method development

Silica hydride, or Type C silica, has been developed as an alternative chromatographic support material for liquid chromatography. There are various bonded phases available with this new support. For four such phases (Cholesterol, Bidentate C18, Diamond Hydride, and Diol), retention and selectivity behavior were investigated using liquid chromatography coupled with triple quadrupole mass spectrometry. A set of small molecules from several chemical classes of interest, and varying in their physicochemical properties, were chromatographed under both reversed-phase and aqueous normal phase modes. To screen the columns, column switching was performed using an automated platform controlled by associated software and an additional valve. A typical scouting gradient was implemented. The separation conditions were not further optimized since the goal was simply to evaluate the variable retention behavior of the phases and selectivity under generic conditions. Further, retention of the analytes were evaluated under isocratic conditions with varying percentages of organic phase to visualize the potential for dual retention modes on the same column for certain analytes. Four analytes (fentanyl, hydrocodone, hydromorphone, and matrine) showed dual mode retention behavior with all four phases. Especially, fentanyl exhibited dramatic “U-shaped” retention profiles on Cholesterol and Bidentate C18 phases. Overall, changes in the retention order between reversed phase and aqueous normal phases emphasized the potential for altered selectivity. Results showed that the Cholesterol phase provided the highest retention for most analytes compared to the other phases. The more polar Diol phase still provided good retention in reversed phase mode. Retention and selectivity were all highly reproducible.

Liquid Chromatography with mass spectrometry analysis of mycotoxins in food samples using silica hydride based stationary phases

Liquid chromatography with mass spectrometry analysis of selected food samples using silica hydride stationary phases allowed for the identification and quantification of common mycotoxins including aflatoxin B1, B2, G1, G2, ochratoxin A, and fumosinin B1. Phenyl and C18 columns showed relatively similar selectivity based on hydrophobicity but the phenyl phase provides an additional mechanism, π-π interaction. The most hydrophobic of the analyzed compounds was more strongly retained on the C18 column and also has fewer unsaturated sites, which limited the interaction with the phenyl phase. Bean, maize, rice, and wheat samples were harvested and stored under conditions conducive to fungal development, and all samples presented toxin contamination exceeding the maximum tolerable limits.

Phenolic composition of pomegranate peel extracts using an liquid chromatography-mass spectrometry approach with silica hydride columns.

The peels of different pomegranate cultivars (Molla Nepes, Parfianka, Purple Heart, Wonderful and Vkunsyi) were compared in terms of phenolic composition and total phenolics. Analyses were performed on two silica hydride based stationary phases: phenyl and undecanoic acid columns. Quantitation was accomplished by developing a liquid chromatography with mass spectrometry approach for separating different phenolic analytes, initially in the form of reference standards and then with pomegranate extracts. The high-performance liquid chromatography columns used in the separations had the ability to retain a wide polarity range of phenolic analytes, as well as offering beneficial secondary selectivity mechanisms for resolving the isobaric compounds, catechin and epicatechin. The Vkunsyi peel extract had the highest concentration of phenolics (as determined by liquid chromatography with mass spectrometry) and was the only cultivar to contain the important compound punicalagin. The liquid chromatography with mass spectrometry data were compared to the standard total phenolics content as determined by using the Folin-Ciocalteu assay.

Investigation of the temperature dependence of water adsorption on silica-based stationary phases in hydrophilic interaction liquid chromatography

In the present work, the adsorption of water was investigated in aqueous normal-phase liquid chromatography on Cogent Silica C and Cogent Phenyl hydride stationary phases at different temperatures by frontal analysis – using coulometric Karl Fischer titration – to compare the temperature dependence of adsorption of water from aqueous acetonitrile.The Cogent Silica-C and Cogent Phenyl Hydride columns have a silicon hydride surface (silica hydride) with less than 2% free silanol group; therefore, they do not have a strong association with water. The adsorption behavior of water on the mentioned stationary phases was modeled by Langmuir isotherm. The preferentially adsorbed water was expressed in terms of a hypothetical monomolecular water layer equivalent in the inner pores. The uptake of water slightly depends on the temperature.The adsorbed water may fill four to eight percent of the pore volume over the studied temperature range, which approximately corresponds to the equivalent of 0.24–0.68 water layer coverage of the adsorbent surface. The phenyl hydride stationary phase shows decreased water uptake in comparison to the Silica C stationary phase.

Quantitative Analysis of Uric Acid Metabolites in Urine by High Performance Liquid Chromatography - Mass Spectrometry Using Silica Hydride Columns

Background: Monitoring of uric acid levels is of significant importance for the prevention of conditions such as gout and kidney disease. Likewise, the metabolites produced from reaction of uric acid with reactive oxygen species are indicative of the level of oxidative stress. Quantitative methods are therefore needed for measuring these compounds in biological sample matrices. Keywords: 6-aminouracil, allantoin, aqueous normal phase, diol, hyperuricemia, silica hydride, uric acid.