Μm Silica Particles Research Articles

Effects of aging of radioactive fallout on timely decontamination of concrete using low and mild pressure washing

Timely decontamination will reduce the consequences of a radiological contamination event. For this purpose, pressure washing can be rapidly deployed, but its effectiveness will change if the interactions between the surface and radionuclides changes as the contamination “ages” under the influence of time and precipitation. While effects of this aging have been reported for dissolved cesium, they have not been studied for radionuclides present as particulate, e.g., fallout. This work studied the effects of aging on decontamination with low (<280 kPa/40 psi) and mild (14,000 kPa/2000 psi) pressure washing, on concrete contaminated with surrogate fallout consisting of soluble Cs-137, 0.5 μm silica particles, and 2 μm silica particles. The samples were aged up to 59 days (time between contamination and decontamination) with and without simulated precipitation. The percent removal following decontamination of the soluble cesium decreased over the first ten days of aging until the removals were less than 10 % for both low and mild pressure washing. The particle decontamination was independent of aging time but decontaminating via mild pressure washing (>80 % particle removal) significantly outperformed decontaminating by low pressure washing by flowing solution across (parallel to) the contaminated surface (<25 % particle removal). The observed changes in decontamination efficacy are explained via measurements of the penetration depth of contaminants. For soluble cesium, the results compared favorably with prior studies and theoretical treatment of cesium penetration, and they yielded additional insight into the effect of washing pressures on decontamination. There are no comparable studies for particulate contamination, so this study resulted in several novel observations which are operationally important for timely decontamination of surfaces following a radiological incident. It also suggests an evidence-based pressure washing procedure for timely decontamination of soluble and insoluble radionuclides which can be used throughout the emergency phase and into the early recovery phase.

Non-enantioselective, enantioselective, and two-dimensional liquid chromatography coupled with tandem mass spectrometry for the study of stereochemical disposition of oxylipins in cGMP-regulated hemin-treated platelets

Oxylipins are important low abundant signaling molecules in living organisms. In platelets they play a primary role in platelet activation and aggregation in the course of thrombotic events. In vivo, they are enzymatically synthesized by cyclooxygenases, lipoxygenases, or cytochrome P450 isoenzmes, resulting in diverse polyunsaturated fatty acid (FA) metabolites including hydroxy-, epoxy-, oxo-FAs, and endoperoxides with pro-thrombotic or anti-thrombotic effects. In a recent study, it was reported that hemin induces platelet death which was accompanied by enhanced reactive oxygen species (ROS) production (measured by flow cytometry) and lipid peroxidation (as determined by proxy using flow cytometry with BODIPY-C11 as sensor). Lipidomic studies further indicated significant changes of the platelet lipidome upon ex vivo hemin treatment, amongst others oxylipins were increased. The effect could be (at least partly) reversed by riociguat/diethylamine NONOate diethylammonium salt (DEA/NO) which modulates the soluble guanylate cyclase(sGC)-cGMP-cGMP-dependent protein kinase I(cGKI) signaling axis. In the original work, oxylipins were measured by a non-enantioselective UHPLC-tandem-MS assay which may not give the full picture whether oxylipin elevation is due to ROS or by enzymatic processes. We present here the study of the stereochemical disposition of hemin-induced platelet lipidome alterations using Chiralpak IA-U column with amylose tris(3,5-dimethylphenylcarbamate) chiral selector immobilized on 1.6 µm silica particles. It was found that the major platelet oxylipins 12-HETE, 12-HEPE and 14-HDoHE (from 12-LOX) and 12-HHT (from COX-1) were present in S-configuration indicating their enzymatic formation. On the other hand, both R and S enantiomers of 9- and 13-HODE, 11- and 15-HETE were detected, possibly due to enzyme promiscuity rather than non-specific oxidation (by ROS or autoxidation), as confirmed by multi-loop based two-dimensional LC-MS using selective comprehensive mode with achiral RPLC in the 1st dimension and chiral LC in the 2nd using a multiple heart-cutting interface. For 12-HETrE, a peak at the retention time of the R-enantiomer was ruled out as isobaric interference by 2D-LC-MS. In particular, arachidonic acid derivates 12(S)-HHT, 11(R)-HETE and 15(S)-HETE were found to be sensitive to hemin and cGMP modulation.

Chiral Hydroxy Metabolite of Mebendazole: Analytical and Semi-Preparative High-Performance Liquid Chromatography Resolution and Chiroptical Properties.

Mebendazole (MBZ) is a benzimidazole carbamate anthelmintic used worldwide for the treatment and prevention of parasitic disorders in animals and humans. A large number of in vivo and in vitro studies have demonstrated that MBZ also has anticancer activity in multiple types of cancers. After oral administration, the phenylketone moiety of MBZ is rapidly reduced to the hydroxyl group to form the chiral hydroxy metabolite (MBZ-OH). To the best of our knowledge, there is no information in the literature on the stereochemical course of transformation and the anthelmintic and antitumor activity of individual enantiomers of MBZ-OH. In the present study, we describe in detail the direct HPLC resolution of MBZ-OH on a 100 mm × 4.6 mm Chirapak IG-3 column packed with 3 μm silica particles containing amylose (3-chloro-5-methylphenylcarbamate) as a selector. At 25 °C and using pure methanol as the mobile phase, the enantioseparation and resolution factors were 2.38 and 6.13, respectively. These conditions were scaled up at a semi-preparative scale using a 250 mm × 10 mm Chiralpak IG column to isolate multi-milligram amounts of both enantiomeric forms of the chiral metabolite. The chiroptical properties of the collected enantiomers were determined and, through a theoretical study, were related to the more stable conformations of MBZ-OH. The first and second eluted enantiomers were dextrorotatory and levorotatory, respectively, in dimethylformamide solution. Finally, by recording the retention factors of the enantiomers as the water content in the water-acetonitrile mobile phases was progressively varied, U-shaped retention maps were generated, indicating a dual and competitive hydrophilic interaction liquid chromatography and reversed-phase liquid chromatography retention mechanism on the Chirapak IG-3 chiral stationary phase.

Improving the Current European Pharmacopoeia Enantio-Selective HPLC Method for the Determination of Enantiomeric Purity in Atorvastatin Calcium Salt Drug Substance

Atorvastatin (ATV) is a well-established lipid-lowering agent. ATV has two stereogenic centers, and of the four possible stereoisomers, only the (3R,5R) form is used therapeutically. The European Pharmacopoeia (EP) monograph 2022 for ATV calcium salt describes a normal-phase high-performance liquid chromatography (HPLC) method for the determination of enantiomeric purity in both drug substance and working standard samples, based on a 150 mm × 4.6 mm Chiralpak AD-H column. The main problems with this method are the very long analysis time and the high solvent consumption. Here, an alternative chromatographic protocol was developed using the Chiralpak AD-3 column (250 mm × 4.6 mm) packed with 3 μm silica particles instead of the 5 μm silica particles of the Chiralpak AD-H chiral stationary phase and characterized by the same polysaccharide selector, amylose-tris(3,5-dimethylphenylcarbamate). Using a mobile phase consisting of a mixture of n-hexane-ethanol-formic acid 90:10:0.1 (v/v/v) as the mobile phase and setting the flow rate and column temperature to 1.0 mL min−1 and 35 °C, respectively, a simultaneous stereo-selective separation was achieved within 35 min without observing any overlap between the enantiomeric impurity peak and peaks related to other ATV impurities. Compared to HPLC EP conditions, the analysis time to elute all the potentially related substances was faster and significantly less mobile phase volume was required. The linearity of the method has been demonstrated in the range of 4.4 μg mL−1 to 1000 μg mL−1 (R2 &gt; 0.999). At a concentration of 4.4 μg mL−1, which is 0.075% of the test solution (5.8 mg mL−1, as ATV free acid), the signal-to-noise ratio was found to be 20.

Simulation of particle deposition on solar photovoltaic panels based on a new critical capture velocity criterion

Solar energy, as a clean energy source, is becoming increasingly important in the global energy mix. However, particle deposition on the surface of photovoltaic (PV) panels can significantly reduce their power generation efficiency. In this study, the collision-deposition behaviour between silica particles and the surface of PV modules is investigated. The impact process of 13 μm silica particles on the glass surface was recorded by using a high-speed digital camera at various incident velocities and angles. A particle dynamics model was developed to predict the critical capture velocity of particles at different incident angles. It was observed that the critical capture velocity of the particles decreases as the angle of incidence increases. Subsequently, a correlation equation was established between the incident angle and the critical capture velocity, serving as the deposition criterion. Computational Fluid Dynamics (CFD) numerical simulation was employed to simulate particle deposition on PV surfaces under different wind speeds and installation tilting angles. The simulation results demonstrate that the mass of 13 μm silica particles deposited on the surface of PV panels decreases with increasing wind speed. Moreover, under identical inlet wind speeds, the particle deposition mass exhibits an initial decrease followed by a subsequent increase as the installation tilt angle of the PV panel increases. The distribution pattern of particle deposition on PV panel surfaces is diverse; however, predominantly concentrated at the mid-bottom region.

Experimental investigation on flow splitting for the elimination of localized secondary flow in cyclones and enhancement of their performance

The limitation of cyclone performance is attributed to the presence of localized secondary flow, including longitudinal circulation, short circuit flow and eccentric circulation. The present study proposes an enhanced cyclone with split flow (ECSF) to effectively suppress the local secondary flow in cyclones. An experimental setup was constructed to evaluate the performance of ECSF under various operating conditions. The results of the experiment demonstrate that the separation efficiency of ECSF surpasses that of Lapple cyclone due to the synergistic effect of split flows in both the by-pass flow and underflow. When the feed velocity is 13 m/s, the ECSF exhibits a reduced separation efficiency of 89.8% for 10 μm silica particles, which surpasses that of the Lapple cyclone by 10.6%. The ECSF achieves its maximum total and reduced separation efficiencies at a feed velocity of 27 m/s, reaching values of 96.3% and 95.7%, respectively. Compared to the Lapple cyclone, the ECSF demonstrates an extended range of operational capabilities with respect to feed velocity. By maintaining a constant total split ratio in ECSF while increasing the proportion of by-pass flow, it is possible to improve its separation efficiency without augmenting overall energy consumption. The findings of this investigation offer valuable insights for enhancing the dust removal efficiency of cyclones.

Changes in the properties of kenaf/silica/epoxy hybrid composites by variations in silica particle sizes and contents

Silica micro-/nanoparticle reinforced composites have been extensively investigated. This study was carried out in two stages. In the first stage, 25 vol.% untreated kenaf fiber, 2 vol.% silica microparticles (>100, 74, 37 µm), and 73 vol.% epoxy resin were fabricated to be the composites by cold-press molding for 24 hours, then subjected to the tensile test to identify the highest composite’s tensile strength corresponding to SEM of the fracture surface. The highest value from the first stage was used in the second stage to determine the influence of the silica particle contents of 1, 3, and 5 vol.% on the composite’s tensile properties and water absorption rate. These results achieved an optimum kenaf/silica/epoxy composite’s tensile properties (64.10 MPa for tensile strength and 6.60 MPa for tensile modulus) by 37 µm silica particle size and 2 vol.% silica content. However, the composite containing 5 vol.% silica reached the lowest water absorption rate of 7.40%.

Assessing biocompatibility & mechanical testing of 3D-printed PEEK versus milled PEEK

ObjectivesTo compare mechanical properties of 3D-printed and milled poly-ether-ether-ketone (PEEK) materials. To define post-production treatments to enhance biocompatibility of 3D-printed PEEK. MethodsStandardised PEEK samples were produced via milling and fused-deposition-modelling 3D-printing. To evaluate mechanical properties, tensile strength, maximum flexural strength, fracture toughness, and micro-hardness were measured.3D printed samples were sandblasted with 50 or 125 μm aluminium oxide beads to increase biocompatibility.Scanning electron microscopy (SEM) evaluated microstructure of 3D-printed and sandblasted samples, estimating surface roughness at scales from 1mm-1μm.Cell adhesion on 3D printed and sandblasted materials was evaluated by culturing primary human endothelial cells and osteoblasts (HUVEC, HOBS) and evaluating cell growth over 48 h. Results3D printed materials had lower tensile strength, flexural strength, and fracture toughness, but higher micro-hardness.SEM analysis of 3D-printed surfaces showed sandblasting with 125 and 50 μm silica particles removed printing defects and created roughened surfaces for increased HUVEC and HOBs uniform cell adhesion and distribution. No cytotoxicity was observed over a 48h period, and all cells demonstrated >95% viability. Clinical significance3D-printing of PEEK is an emerging technology with clear advantages over milling in maxillofacial implant production. Nonetheless, this manufacturing modality may produce 3D printed PEEK devices with lower mechanical resistance parameters compared to milled PEEK but with values compatible with natural bone. PEEK has poor osteoconductivity and ability to osseointegrate. Sandblasting is an inexpensive modality to remove irregular surface defects and create uniform micro-rough surfaces supporting cell attachment and potentially enhancing integration of PEEK implants with host tissue.

Continuous Particle Separation Driven by 3D Ag-PDMS Electrodes with Dielectric Electrophoretic Force Coupled with Inertia Force.

Cell separation has become @important in biological and medical applications. Dielectrophoresis (DEP) is widely used due to the advantages it offers, such as the lack of a requirement for biological markers and the fact that it involves no damage to cells or particles. This study aimed to report a novel approach combining 3D sidewall electrodes and contraction/expansion (CEA) structures to separate three kinds of particles with different sizes or dielectric properties continuously. The separation was achieved through the interaction between electrophoretic forces and inertia forces. The CEA channel was capable of sorting particles with different sizes due to inertial forces, and also enhanced the nonuniformity of the electric field. The 3D electrodes generated a non-uniform electric field at the same height as the channels, which increased the action range of the DEP force. Finite element simulations using the commercial software, COMSOL Multiphysics 5.4, were performed to determine the flow field distributions, electric field distributions, and particle trajectories. The separation experiments were assessed by separating 4 µm polystyrene (PS) particles from 20 µm PS particles at different flow rates by experiencing positive and negative DEP. Subsequently, the sorting performances of the 4 µm PS particles, 20 µm PS particles, and 4 µm silica particles with different solution conductivities were observed. Both the numerical simulations and the practical particle separation displayed high separating efficiency (separation of 4 µm PS particles, 94.2%; separation of 20 µm PS particles, 92.1%; separation of 4 µm Silica particles, 95.3%). The proposed approach is expected to open a new approach to cell sorting and separating.

Fast liquid chromatography method for separation of peptides using a sub-2 μm ground silica monolith packed column.

A stationary phase based on sub-2 μm ground silica monolith particles was fabricated by in situ polymerization and applied in micro-column for separation of peptides. The sub-2 μm silica particles were obtained from monolith using sol-gel process followed by grinding and sedimentation to remove the fines. Initially, the silica monolith particles were pretreated with 3-trimethoxysilyl propyl methacrylate to attach double-bonded ligands onto the surface, then a network structure was formed onto the surface of the particle using styrene, N-isopropylacrylamide, and ethylene glycoldimethacrylate. The effect of the flow rate of the mobile phase on the separation performance was investigated. The stationary phase was characterized by field emission scanning electron microscopy, thermogravimetry, particle size distribution, and element analysis. The resultant phase was packed in glass-lined stainless steel micro-columns (2.1 mm × 50 mm) and evaluated for fast separation. An average number of theoretical plates as high as 9800 plates/column (5.10 μm plate height) was achieved for five synthetic peptides under the optimized flow rate of 0.15 mL/min. The repeatabilities of column-to-column, intraday, and interday through relative standard deviation were found better than 4%, exhibiting satisfactory repeatability of the developed micro-column for fast separation of peptides.

Direct enantioselective gradient reversed-phase ultra-high performance liquid chromatography tandem mass spectrometry method for 3-hydroxy alkanoic acids in lipopeptides on an immobilized 1.6μm amylose-based chiral stationary phase.

3-Hydroxy fatty acids are important chiral building blocks of lipopeptides and metabolic intermediates of fatty acid oxidation, respectively. The analysis of the stereochemistry of such biomolecules has significant practical impact to elucidate and assign the enzymatic specificity of the biosynthesis machinery. In this work, a new mass spectrometry compatible direct chiral ultra high performance liquid chromatography separation method for 3-hydroxy fatty acids without derivatization is presented. The application of amylose tris(3,5-dimethylphenyl carbamate) based polysaccharide chiral stationary phase immobilized on 1.6μm silica particles (CHIRALPAK IA-U) allows the enantioseparation of 3-hydroxy fatty acids under generic electrospray ionization mass spectrometry friendly reversed phase gradient elution conditions. Adequate separation factors were achieved with both acetonitrile and methanol as organic modifiers, covering hydrocarbon chain lengths between C6 and C14 . Elution orders were derived from rhamnolipid (R-95) of which enantiomerically pure or enriched (R)-3-hydroxy fatty acids were recovered after ester hydrolysis. The S-configured acids consistently eluted before the respective R-enantiomers. The method was successfully applied for the elucidation of the absolute configuration of 3-hydroxy fatty acids originating from a novel lipopeptide with unknown structure. The work furthermore demonstrates that gradient elution is a viable option also in enantioselective (ultra)high performance liquid chromatography, even for analytes with modest separation factors, although less commonly exploited.

A detailed study of the interaction between levitated microspheres and the target electrode in a strong electric field

In this work, we report on an in-depth study of how 10 μm silica and polystyrene particles interact with a target electrode after they were levitated by applying a strong electric field. The results show that, under these conditions, silica particles unexpectedly have a higher tendency to adhere on a fluorocarbon coated electrode compared to a bare, non-coated silicon electrode. Relative adherence ratios Γ up to Γ = 4.7 were observed. Using the colloidal probe technique, atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM), the observations can be explained by a mechanism where particles dissipate their energy through adhesive forces combined with permanent surface deformations during impact and charge transfer through the contact electrification phenomenon. All these processes attribute to increasing the probability that levitated particles attain velocities that are lower than the sticking velocity.

Recovery of Filtered Particles by Elastic Flat-Sheet Membrane with Cross Flow.

After filtration, filtered residue is recovered by a spoon, during which, the structure of the residue is destroyed, and the activity of the microorganism would be reduced. Thus, a more efficient recovery method of filtered residue is required. This study addressed the recovery method of filtered residue by the restoration of an elastic membrane, followed by cross flow. An elastic membrane composed of a copolymer of poly(ethylene glycol) diacrylate and polyacrylonitrile was prepared by photopolymerization. The pore diameter of the obtained membrane was about 10 μm. Silica particle (1 and 10 μm) and Nannochloropsis sp. (2 μm) suspension was filtered, demonstrating that silica particles of 10 μm were filtered perfectly, whereas the filtration percentage of 1 μm silica particles and Nannochloropsis sp. was lower. After the filtration, the applied pressure was released to restore the elastic membrane which moved the filtered particles up, then the filtered residue was recovered by cross flow above the membrane, demonstrating that 71% of the filtered 10 μm silica particles was recovered. The elastic behavior of the membrane, along with the cross flow, has the potential to be used as a technique for the recovery of the filtered residues. This proposed scheme would be used for the particle recovery of ceramics, cells, and microorganisms from a lab scale to a large-scale plant.

Through-pore polymerization in polar high-performance liquid chromatography columns allowing scanning electron microscopy based imaging of the packing order

To allow an enhanced understanding of the order in packed HPLC columns, in this work a methodology for immobilizing native polar silica particles is developed based on the polymerization of a methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) as a cross-linker in the interstitial pores of HPLC columns. Subsequent mechanical cutting then allows scanning electron microscopy (SEM) based imagery of cross-sections of the packed bed. In this way, the packing efficiency of home-made and commercial HPLC columns with 4.6 mm inner diameter and 150 mm length comprising the same packing material of 5 µm silica particles are compared. The methodology is developed for native silica used in e.g. hydrophilic interaction liquid chromatography (HILIC) and in normal phase LC. In order to confirm the feasibility of the developed methodology, the conventional methods for the evaluation of column, efficiency and porosity, are also employed. The obtained porosity information is compared and showed the same trend with the external porosity measurements obtained via inverse size exclusion approach, illustrating its potential application to study the micro-heterogeneity of packed HPLC columns and to guide the optimization of the packing process of HPLC columns.

Formation of oil-particle aggregates: Particle penetration and impact of particle properties and particle-to-oil concentration ratios

Oil droplets in marine environment interact with particles to form oil particle aggregates (OPA), and alters the transport and fate of oil. We investigated the impact of particles properties on the formation of OPAs. It was found that the distribution of 9 μm spherical silica (sand) particles on the oil droplet was more uniform than the 3 μm silica particles, and it is likely due to the inertia of the larger particles causing them to lodge into the droplet. Also, the OPAs of the 3 μm silica particles were much smaller than those of the 9 μm particles. For kaolinite particles that are rod-like of length around 10 μm, it was found that increasing the hydrophobicity of the particles from a contact angle (CA) of ~ 29o to 38o, increases the penetration of the particles in the oil through a projectile penetration mechanism, whereby the particle possesses sufficient inertia to penetrate into the oil. However, a further increase in hydrophbocitiy (CA ~ 57o) caused the particles to agglomerate together and avoid the oil droplets. The oil droplets got smaller with time probably due to the penetration of the particles in them. For an oil concentration of 500 mg/L, a particle concentration of 100 mg/L was incapable of fragmenting the oil droplets, but particle concentration of 500 mg/L fragmented the droplets similarly to a concentration of 1500 mg/L. This is due to the larger coverage of the droplet surface area by the particles and the subsequent weakening of its structural rigidity through the reduction of the oil-water interfacial tension. The study shows that the fate (e.g., after 24 h) of OPAs greatly depends on the type of sediments where the oil spilled (sand versus clay) and their concentration.

Precursor carboxy-silica for functionalization with interactive ligands. I. Carbodiimide-assisted preparation of silica-bonded stationary phases with octadecyl, naphthyl, and anthracenyl ligands: Comparison of their selectivity and retentivity.

A precursor carboxy-silica support was introduced for grafting retentive ligands for use in high-performance liquid chromatography. This support was prepared by sequentially reacting 5μm silica particles with vinyltrimethoxysilane and then thioglycolic acid. The carboxy-silica thus obtained was subsequently functionalized with octadecylamine, 2-naphthylamine, or 2-aminoanthracene by on-column reactions via a carbodiimide conjugation reaction. The carbodiimide with its zero-length carboxyl-to-amine coupling ability works by activating the surface carboxyl groups of the precursor support for direct reaction with the primary amines of octadecylamine, 2-naphthylamine, or 2-aminoanthracene via amide bond formation. These reactions series, which are applied for the first time in high-performance liquid chromatography column fabrication, yielded the octadecyl-, naphthyl-, and anthracenyl-silica columns. The three columns were evaluated for their reversed-phase chromatography retention properties with alkylbenzenes, alkylphenyl ketones, nitroalkanes, benzene and toluene derivatives, polyaromatic hydrocarbons, and nitro-substituted amino acids. The naphthyl- and anthracenyl-silica exhibited a good selectivity and efficiency toward most of the aromatic analytes when compared to the octadecyl-silica. Nitro-substituted amino acids containing electron withdrawing groups showed greater selectivity than other analytes on the aromatic-based columns than the C18 column. This is because of the ability of the π electron system of the analyte to accept electrons from the aromatic-based stationary phase (a Lewis base).

HPLC-UV analytical validation of a method for quantification of progesterone in ex vivo trans-corneal and trans-scleral diffusion studies

Progesterone (PG) diminishes free radical damage and thus can afford protection against oxidative stress affecting the retina. The therapeutic use of PG is limited because it is a highly hydrophobic steroid hormone with very low solubility in water. This is the main drawback for the therapeutic application of PG at ocular level. The aims of this study were: (i) to analyze if PG causes ocular irritation (ii) to validate a HPLC method to determine PG in ex vivo studies and (iii) to evaluate PG permeation through cornea and sclera. A high performance liquid chromatographic method was developed and validated to detect PG incorporated to β-cyclodextrin using a Waters Sunfire C18 (150 × 4.6 mm) reverse-phase column packed with 5 μm silica particles using a mobile phase consisted of a mixture of acetonitrile (ACN) and pure water 80:20 (v/v), pH 7.4. The limit of detection and the limit of quantification for 50 μL injection of PG were found to be 0.42 and 1.26 μg/mL, respectively. The calibration curve showed excellent linearity over the concentration range (0.5 μg/mL to 100 μg/mL). As proof of concept, ex-vivo experiments to investigate PG permeation through cornea and sclera with vertical diffusion cells were carried out to quantify PG diffusion. Ex vivo experiments demonstrate its applicability to investigate permeation levels of PG from 6.57 ± 0.37 μg/cm2 at cornea and 8.13 ± 0.85 μg/cm2 sclera. In addition, at the end of diffusion studies the amount of PG retained in each tissue was also quantified, and it was 40.87 ± 9.84 μg/cm2 (mean ± SD; n = 6) in cornea and 56.11 ± 16.67 μg/cm2 (mean ± SD; n = 6) in sclera.

Imidazolium ionic liquid bonded silica stationary phases: Part I: Hexadecylimidazolium stationary phase

In this first research report, the design of an ionic liquid (IL) silica based stationary phase is described and characterized chromatographically using standard solute probes and via physical measurements including Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The stationary phase is hexadecylimidazolium bonded to silica microparticles for the retention of various small and large solutes primarily by reversed-phase retention mechanism and to some different extent via π-π interactions and electrostatic interactions. The hexadecylimidazolium functionalized silica stationary phase was obtained by first grafting the surface of 5 µm silica particles with 3-chloropropyltrimethoxysilane forming the so-called a primary sublayer followed by attaching a top layer of hexadecylimidazole, thus resulting in the formation of IL based reversed-phase column. The hexadecylimidazolium column thus obtained exhibited relatively symmetrical peak shapes and high separation efficiencies for the studied analytes with a wide array of functional groups including ionizable analytes. The observed unique retention characteristics and selectivity of the hexadecylimidazolium column can be attributed to its multi interactions with various solutes including hydrophobic, electrostatic, π–π and hydrogen bonding interactions. Abbreviations: ABs: alkylbenzenes; APKs:n-alkyl phenyl ketones; CPS: chloropropylsilyl-silica; CPTMS: chloropropyltrimethoxysilane; HILIC: hydrophilic interaction chromatography; ILs: ionic liquids; IPA: isopropyl alcohol; TFA: trifluoroacetic acid; TGA: thermogravimetric analysis; THF: tetrahydrofuran; PAHs: polyaromatic hydrocarbons

Investigating the use of unconventional temperatures in supercritical fluid chromatography

The use of unorthodox temperatures, ranging from −5 °C up to 80 °C, have been thoroughly investigated in supercritical fluid chromatography. To this purpose, an initial evaluation of the kinetic and thermodynamic performance has been made with a set of 4 analytes eluting at different percentages of organic co-solvent in the mobile phase (3%–10% - 45%–80%). The van Deemter plots have demonstrated how, at low organic modifier presence, the use of low temperatures did not necessarily translate into worse performance, while high temperatures could pose more issues due to the poor handling of the super/subcritical mobile phase by the chromatographic system. With important percentages of co-solvent, however, high temperatures were fundamental in ensuring better profiles of the van Deemter plots, compared to low temperatures. Pressure plots have demonstrated that gradients reaching elevated percentages of organic modifiers can also be used on stationary phases packed with sub 2 μm silica particles if high temperatures are employed. The thermodynamic evaluation, made via the analysis of van’t Hoff plots, indicates the presence of three retention behaviors happening in UHPSFC when switching from high to low temperatures, depending on the co-solvent percentage needed to elute one analyte. Finally, an assessment of the stationary phase stability at high temperatures was performed: the retention times variabilities recorded were minimal (RSD < 2.5%), as well as the peak widths and inlet column pressures were somewhat constant throughout the analyses.In the second part of this study, a focus on potential applications benefiting from such unconventional temperatures has been made. A series of challenging analytes have experienced better chromatographic resolution at either high or low temperatures, providing therefore a potentially interesting tool to analysts during the chromatographic method development process. In conclusion, the UV sensitivity at different temperatures was also taken into consideration, with no significant impact on the quality of the UV signal under any condition.

Fast UHPLC enantioseparation of liquid crystalline materials with chiral center based on octanol in reversed-phase and polar organic mode

Fast baseline enantioseparation of twenty racemic liquid crystalline compounds was carried out via ultra-performance liquid chromatography through direct enantioseparation in polar organic and reversed-phase modes. Tris(3-chloro-5-methyl-phenylcarbamate) derivative of amylose was used as chiral stationary phase; the chiral selector was covalently immobilized on sub-2 µm silica particles. Experiments were done using either pure acetonitrile as mobile phase or simple binary mobile phases consisting of acetonitrile/water mixtures in different volume ratios. No buffers or additives were used. Studied materials are a set of structurally similar compounds comprising two different structures of chiral center, various length of alkoxy spacer and four patterns of lateral substitution of aromatic core by fluorine. The compounds do not contain any ionizable group. The effect of the enantiomer structure on the retention and enantioseparation was evaluated. Flow rate and column temperature were optimized as part of method development.