Showing papers on "Silica gel published in 2023"

Natural growth of gold dendrites within silica gels

Abstract: High-grade ores in low-sulfidation epithermal precious metal deposits include banded quartz veins that contain gold dendrites. The processes by which dendrite growth takes place have been subject to debate for decades, especially given that these deposits are known to form from dilute thermal liquids that contain only trace amounts of gold. It is shown here that growth of gold dendrites in epithermal veins at the McLaughlin deposit in California (western USA) originally took place within bands of gel-like noncrystalline silica. The gel provided a framework for the delicate dendrites to form. The high permeability of the gel allowed the diffusion and advection of gold from the thermal liquids flowing across the top of the silica layers to the sites of crystal growth within the gel. Over time, the gel hardened to form opal-AG. This silica phase is thermodynamically unstable and recrystallized to quartz that has a distinct mosaic texture.

Synthesis of Low Density and High Purity Silica Xerogels from South African Sugarcane Leaves without the Usage of a Surfactant

Abstract: Sugarcane leaves were used to produce high-purity and low-density silica xerogels through a sol–gel method. The biogenic silica produced through a thermochemical method was reacted with sodium hydroxide (NaOH) to form sodium silicate and the produced sodium silicate was titrated with 1 M citric acid to form silica gel. The formed silica gel was washed, subjected to a solvent exchange process and later dried at 80 °C to produce low-density and high-purity silica xerogels. The produced xerogels were characterized with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), nitrogen physisorption, elemental analysis (CHNS), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The produced silica xerogels had an amorphous structure and purity of 99.9 wt%. In addition, the textural properties analysis showed that the xerogel has a BET surface area of 668 m2·g−1, an average pore diameter of 7.5 nm, a pore volume of 1.26 cm3·g−1 and a density of 0.23 g·cm−3.

Method Development for Purification of γ-oryzanol from Hydrolyzed Rice Bran Acid Oil by Semi-preparative Chromatography.

Abstract: The objective of this study was to develop a method for isolation and purification of γ-oryzanol from hydrolyzed rice bran acid oil (RBAO) using semi-preparative chromatography by first applying silica coated-thin layer chromatography (TLC) to determine the suitable mobile phase. Subsequently, column chromatography was carried out to determine the effects of purification conditions such as the amount of and particle sizes of the sample silica gel, and elution modes, on the percentage of γ-oryzanol yield and recovery. The results from the TLC suggested that 75:25 (v/v) hexane to ethyl acetate mixture was a suitable mobile phase. The semi-chromatographic results indicated that the column containing 10 g of 25-40 μm silica gel with isocratic elution gave the highest yield (84%) of purified γ-oryzanol (> 95% purity). Further application of a step-gradient elution with 85:15 (v/v), followed by 75:25 (v/v) hexane to ethyl acetate mixture increased chromatographic resolution (Rs), resulting in enhanced separation efficiency, which in turn led to a higher yield of purified γ-oryzanol of 90%.

[A new bibenzyl derivative from stems of Dendrobium officinale].

Abstract: Eleven compounds were isolated from the 95% ethanol extract of the stems of Dendrobium officinale after water extraction by various modern chromatographic techniques, such as silica gel column chromatography(CC), octadecyl-silica(ODS) CC, Sephadex LH-20 CC, preparative thin layer chromatography(PTLC) and preparative high performance liquid chromatography(PHPLC). According to spectroscopic analyses(MS, 1D-NMR, 2D-NMR) combined with optical rotation data and calculated electronic circular dichroism(ECD), their structures were identified as dendrocandin Y(1), 4,4'-dihydroxybibenzyl(2), 3-hydroxy-4',5-dimethoxybibenzyl(3), 3,3'-dihydroxy-5-methoxybibenzyl(4), 3-hydroxy-3',4',5-trimethoxybibenzyl(5), crepidatin(6), alternariol(7), 4-hydroxy-3-methoxypropiophenone(8), 3-hydroxy-4,5-dimethoxypropiophenone(9), auriculatum A(10) and hyperalcohol(11). Among them, compound 1 was a new bibenzyl derivative; compounds 2 and 7-11 have not been previously reported from Dendrobium plants; compound 6 was reported from D.officinale for the first time. Compounds 3-6 exhibited potent antioxidant activity with IC_(50) values of 3.11-9.05 μmol·L~(-1) in ABTS radical scavenging assay. Compound 4 showed significant inhibitory effect on α-glucosidase, with IC_(50) value of 17.42 μmol·L~(-1), indicating that it boasted hypoglycemic activity.

Removal of Methylene Blue from Aqueous Solution by Mixture of Reused Silica Gel Desiccant and Natural Sand or Eggshell Waste

Abstract: The purpose of this work was to develop, characterize and test new low-cost materials suitable for removing methylene blue dye from water and wastewater by adsorption. The solid materials consisted of silica gel powder (SG), silica gel mixed with eggshell powder (SG-ES) and a mixture of silica gel with sand from the western Iraqi desert (SG-SI). The samples were milled by using an electrical mixer and a ball mill, followed by a drying step. In addition, desert sand was acid-treated in order to remove impurities. The structure and chemical composition of the samples were investigated by X-ray diffraction (XRD), a scanning electron microscopy technique equipped with an energy-dispersive X-ray spectrometer (SEM-EDX), a low-temperature nitrogen adsorption (BET) technique, thermo-analytical (TG/TGA) measurements and Fourier-transformed infrared spectroscopy (FTIR). The previously mentioned materials were tested to remove methylene blue from an aqueous solution. The adsorption experiments were monitored by ultraviolet–visible (UV-Vis) spectrophotometry and showed that SG and SG-ES gave promising results for the methylene blue removal from water. After 40 min of treatment of the aqueous solution containing 10 mg/L of MB at room temperature, the tested SG, SG-ES and SG-SI materials were found to have 86%, 80% and 57% dye adsorption efficiency, respectively. Taking into consideration not only the adsorption activity of the studied material but their availability, cost and concepts of cleaner production and waste minimization, the developed silica gel with eggshell can be considered as a good, cost-effective alternative to commercially available activated-carbon-based adsorbents. Different kinetic and isotherm models were fitted to the experimental results. A pseudo-second-kinetics-order model revealed high correlation fitting, while the Freundlich model was found to appropriately describe the adsorption isotherm. The thermal stability during the possible regeneration process of the SG-ES adsorbent mixture and its interaction mechanism with cationic dye was discussed.

Synthesis and Characterization of Novel Thiosalicylate-based Solid-Supported Ionic Liquid for Removal of Pb(II) Ions from Aqueous Solution

Abstract: The main objectives of this study are to synthesize a new solid-supported ionic liquid (SSIL) that has a covalent bond between the solid support, i.e., activated silica gel, with thiosalicylate-based ionic liquid and to evaluate the performance of this new SSIL as an extractant, labelled as Si-TS-SSIL, and to remove Pb(II) ions from an aqueous solution. In this study, 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium thiosalicylate ([MTMSPI][TS]) ionic liquid was synthesized and the formation of [MTMSPI][TS] was confirmed through structural analysis using NMR, FTIR, IC, TGA, and Karl Fischer Titration. The [MTMSPI][TS] ionic liquid was then chemically immobilized on activated silica gel to produce a new thiosalicylate-based solid-supported ionic liquid (Si-TS-SSIL). The formation of these covalent bonds on Si-TS-SSIL was confirmed by solid-state NMR analysis. Meanwhile, BET analysis was performed to study the surface area of the activated silica gel and the prepared Si-TS-SSIL (before and after washing with solvent) with the purpose to show that all physically immobilized [MTMSPI][TS] has been washed off from Si-TS-SSIL, leaving only chemically immobilized [MTMSPI][TS] on Si-TS-SSIL before proceeding with removal study. The removal study of Pb(II) ions from an aqueous solution was carried out using Si-TS-SSIL as an extractant, whereby the amount of Pb(II) ions removed was determined by AAS. In this removal study, the experiments were carried out at a fixed agitation speed (400 rpm) and fixed amount of Si-TS-SSIL (0.25 g), with different contact times ranging from 2 to 250 min at room temperature. The maximum removal capacity was found to be 8.37 mg/g. The kinetics study was well fitted with the pseudo-second order model. Meanwhile, for the isotherm study, the removal process of Pb(II) ions was well described by the Freundlich isotherm model, as this model exhibited a higher correlation coefficient (R2), i.e., 0.99, as compared to the Langmuir isotherm model.

Vapochromism of indolenine-based heptamethine cyanine dye adsorbed on silica gel

Abstract: Herein, we present for the first time an organic–inorganic hybrid material comprising indolenine-based heptamethine cyanine dye adsorbed on silica gel, which shows vapochromism to amines or chlorinated solvents, leading to...

Novel Stability-Indicating TLC-densitometric Method for Quantification of Antazoline Hydrochloride and Tetryzoline Hydrochloride; Application to pharmaceutical formulation

Abstract: Ophthalmic pharmaceutical preparation containing antazoline hydrochloride (ANT) and tetryzoline hydrochloride (TET) is prescribed widely as an over the counter (OTC) medication to treatment allergic conjunctivitis and their determination in presence of their degradation products is a major challenge. A novel sensitive, selective, and precise thin-layer chromatographic method established to determination both ANT and TET in both bulk drugs, formulation, and in presence of their degradation products with the elucidation of degradate's structures. Upon using silica gel plates and means of a developing system using ethyl acetate: ethanol: ammonia (8: 2: 0.1, by volume) the studied drugs separation was achieved, and scanning was carried out at 220.0 nm for the separated bands with a 0.2–18.0 µg/band concentration range for each of ANT and TET. Optimum separation was achieved with values Rf of 0.42 and 0.69, for TET and ANT, respectively. Additionally, the studied drugs' stock solutions were imperiled to different stress conditions. Both drugs were found to be vulnerable to alkaline hydrolysis as well as oxidative degradation showing well resolved degradation products' peaks. While they held out against acidic, thermal and photo degradation. Mass spectrometry was employed to elucidate the degradates' structures. Validity was applied for the proposed method with respect to all validation parameters. Effectively the method was applied to estimate the cited drugs' in marketed ophthalmic formulation.

Application of the green analytical procedure index to the simultaneous analysis of co-formulated tinidazole and ciprofloxacin in pure form, tablet dosage form, and human plasma using an environmentally friendly micellar high-performance thin-layer chromatographic technology

Abstract: Abstract In individuals with chronic refractory pouchitis and other gastrointestinal disorders, the combination of ciprofloxacin (CIP) and tinidazole (TIN) is beneficial and safe. As a result, a green micellar high-performance thin-layer chromatographic (HPTLC) approach for the immediate analysis of TIN and CIP in pure, spiked human plasma, and co-formulated tablet dosage form has been developed. It is rapid, extremely easy, sensitive, cost-effective, and environmentally friendly. The stationary phase was Merck aluminum HPTLC plates covered with silica gel 60 F 254 , while the mobile phase was acetone–ethanol–2% watery sodium dodecyl sulfate (3:4:2, V/V ). For quantification of both medications, the densitometric scanner was set at 310 nm. For TIN and CIP, this chromatographic separation yielded symmetric, compact peaks with R F values of (0.22 ± 0.009) and (0.42 ± 0.007), respectively. At 310 nm, the separated spots were densitometrically scanned. For TIN and CIP, the detection thresholds were 6.7 ng/band and 25.03 ng/band, respectively. For TIN and CIP, the quantification limits were 20.3 ng/band and 75.25 ng/band, respectively. The approach was validated according to International Council for Harmonisation (ICH) principles and then used to determine the researched medicines in their various pharmaceutical dosage forms, and human plasma yielding an exceptional percent of recovery. In terms of precision and accuracy, the results were in great accordance with the published approach. This method is suitable for the sequential analysis of the two drugs in pure form, tablet dosage forms, and spiked human plasma due to its simplicity, speed, greenness, robustness, and low cost.

Green analytical chemistry and experimental design: a combined approach for the analysis of zonisamide

Abstract: Green analytical chemistry principles, as well as experimental design, are a combined approach adopted to develop sensitive reproducible stability indicating HPLC method for Zonisamide (ZNS) determination. The optimal conditions for three chromatographic parameters were determined using a central composite design of the response surface. Kromasil C18 column (150 mm × 4.6 mm, 5 µm) was utilized with ethanol, H2O (30:70 v/v) as a mobile phase at a flow rate of 1 mL/min at 35 °C. Good reproducibility and high sensitivity were achieved along (0.5-10 µg/mL) concentration range. In contrast, the TLC-densitometric method was performed on aluminum plates precoated with silica gel 60F254 as a stationary phase and chloroform: methanol: acetic acid (8:1.5:0.5 by volume) as a developing system. Reproducible results were obtained in the range of (2-10 μg/band). The chromatograms of HPLC and TLC were scanned at 280 nm and 240 nm, respectively. The suggested methods have been validated following ICH guidelines, and no statistically significant differences were detected between the results of the current study and the official USP method. It was also found that using experimental design implements the green concept by reducing the environmental impact. Finally, Eco-Scale, GAPI and AGREE were used to assess the environmental impacts of the suggested methods.

Weak Affinity Chromatography using Organic Solvents on Cyanopropyl- and Arene-Modified Silica-Gel Columns—Structural Demands for Host and Guest Moieties and Effect of Solvents

Abstract: Weak affinity chromatography (WAC) is effective for isolating target compounds from analogous compounds with similar functional groups. Previously, a few chromatographic behaviors based on WAC using organic solvents were observed in a series of cyclic multiporphyrin systems on cyanopropyl-modified silica gel (CN-MS). Here, three cyclic porphyrin trimers with various rigidity were examined on CN-MS to understand the mechanism of the specific interactions between porphyrin derivatives and functional groups on modified silica gel. In addition to CN-MS, six modified silica-gel columns were tested to compare their retention abilities for a cyclic nickel porphyrin dimer (C4Ni2MsCP2). We examined the cosolvent effects of the pyridine eluents for C4Ni2MsCP2. Apparent dissociation constants of C4Ni2MsCP2 with functional groups on the MS columns and effective amounts of the functional groups were estimated by frontal affinity chromatography (FAC). 1H NMR titrations of acetonitrile and nitrobenzene to C4Ni2MsCP2 were conducted to compare their association constants with movable guest molecules to the dissociation constants with immobilized functional groups obtained in FAC. We found rigidity of cyclic porphyrin derivatives and immobilization of functional groups on silica gel is necessary for significant retentions using WAC. The affinity interaction does not occur at the center of C4Ni2MsCP2, but probably occurs on the surface composed of a bipyridyl moiety and the adjacent edges of the two porphyrins. Polar solvents, such as nitrobenzene, acetonitrile, and methanol, weakened the interaction. Although C4Ni2MsCP2 dissolves well in chloroform, the interactions between C4Ni2MsCP2 and the MS columns are considerably strengthened in the presence of chloroform. The competitiveness of solvents and cosolvents with the interaction of the porphyrin on WAC is independent of the solubility of the analyte.

Separation and Purification of Hydroxyl-α-Sanshool from Zanthoxylum armatum DC. by Silica Gel Column Chromatography

Abstract: Hydroxyl-α-sanshool is the main alkylamide produced by Zanthoxylum armatum DC., and it is responsible for numbness after consuming Z. armatum-flavored dishes or food products. The present study deals with the isolation, enrichment, and purification of hydroxyl-α-sanshool. The results indicated that the powder of Z. armatum was extracted with 70% ethanol and then filtrated; the supernatant was concentrated to get pasty residue. Petroleum ether (60–90 °C) and ethyl acetate at a 3:2 ratio, with an Rf value of 0.23, were chosen as the eluent. Petroleum ether extract (PEE) and ethyl acetate–petroleum ether extract (E-PEE) were used as the suitable enriched method. Afterward, the PEE and E-PEE were loaded onto silica gel for silica gel column chromatography. Preliminary identification was carried out by TLC and UV. The fractions containing mainly hydroxyl-α-sanshool were pooled and dried by rotary evaporation. Lastly, all of the samples were determined by HPLC. The yield and recovery rates of hydroxyl-α-sanshool in the p-E-PEE were 12.42% and 121.65%, respectively, and the purity was 98.34%. Additionally, compared with E-PEE, the purity of hydroxyl-α-sanshool in the purification of E-PEE (p-E-PEE) increased by 88.30%. In summary, this study provides a simple, rapid, economical, and effective approach to the separation of high-purity hydroxyl-α-sanshool.

The Contribution of Adsorbent Materials (Silica Gel and Sawdust) in Removing Water Vapor; Iraq as a Study Case

Abstract: This research aims to remove the moisture (latent load) generated by the occupants of the space due to the addition of water vapor resulting from the natural breathing process, the perspiration that evaporates in the air of the space. In sum, the dehumidification system (DS) reduces the amount of latent load or removes it completely to reduce the load on the air conditioner. In this study, adsorbent materials, such as silica gel-Blue and sawdust were used and their effectiveness was compared when used in dehumidification. The results of these experiments for June showed that the adsorption rate and temperature of the blue silica gel - Blue were 20% and 34°C, while the humidity and temperature increased to 52% and 36°C when using sawdust (when rotating the dehumidifying system hourly). Moreover, for July, the adsorption percentages of silica gel-Blue were 8%, while the moisture content of sawdust increased to 49%, while the adsorption percentage in August when using silica gel - Blue was 10% and the relative humidity increased until it reached 39% when using sawdust. While the temperatures in July and August reached their maximum value when using silica gel - Blue and sawdust at 35°C and 36°C, respectively. The water vapor absorption rate in June, July, and August is 83.39 g, 70.82 g, and 65 g, respectively. While the drying process increased during these months due to the increase in solar radiation. Therefore, silica gel - Blue has proven its effectiveness by absorbing moisture more efficiently than sawdust. However, when drying sawdust, it was more effective and faster drying than silica gel - Blue.

Determination of Phosphodiesterase Type-5 Inhibitors (PDE-5) in Dietary Supplements

Abstract: This study proposed a high-performance thin-layer chromatography (HPTLC) screening method to detect phosphodiesterase 5 (PDE-5) inhibitors as possible adulterant agents in various dietary supplements. Chromatographic analysis was performed on silica gel 60F254 plates using a mixture of ethyl acetate:toluene:methanol:ammonia in a volume ratio of 50:30:20:0.5 as a mobile phase. The system provided compact spots and symmetrical peaks of sildenafil and tadalafil with retardation factor values of 0.55 and 0.90, respectively. The analysis of products purchased from the internet or specialized stores demonstrated the presence of sildenafil, tadalafil, or both compounds in 73.3% of products, highlighting inadequacies and inconsistencies in the labeling, as all dietary supplements were declared to be natural. The results were confirmed using ultra-high-performance liquid chromatography coupled with a positive electrospray ionization high-resolution tandem mass spectrometry (UHPLC-HRMS-MS) method. Furthermore, in some samples, vardenafil and various analogs of PDE-5 inhibitors were detected using a non-target HRMS-MS approach. The results of the quantitative analysis revealed similar findings between the two methods, with adulterant quantities found to be similar to or higher than those in approved medicinal products. This study demonstrated that the HPTLC method is a suitable and economical method for screening PDE-5 inhibitors as adulterants in dietary supplements intended for sexual activity enhancement.

Development of thin layer chromatographic densitometric method for simultaneous quantification of Ivabradine HCl and Bisoprolol fumarate

Abstract: The literature review reveals that no thin-layer chromatographic method has been developed for the simultaneous estimation of Bisoprolol fumarate and Ivabradine HCl in the combined dosage form. A sensitive, precise, accurate, and robust thin-layer chromatographic method was developed and validated for the simultaneous quantification of a newer combination of Bisoprolol fumarate and Ivabradine HCl used in the treatment of angina, according to the International Council for Harmonization Q2 (R1) guideline. The stationary phase was pre-coated silica gel aluminum plate 60 F254 and toluene‒methanol-triethylamine (9:1:0.1, v/v/v) was used as the mobile phase. A common detection wavelength of 279 nm was selected for the simultaneous quantification of Bisoprolol fumarate and Ivabradine HCl. The method was validated for different parameters like linearity, precision, accuracy, robustness, the limit of detection, and the limit of quantification as per the International Council for Harmonization guidelines. The correlation coefficients (r2) for Bisoprolol fumarate and Ivabradine HCl were found to be 0.9976 and 0.9965, respectively. The mean percentage recoveries for Bisoprolol fumarate and Ivabradine HCl were found to be 99.19%–101.70% and 98.71%–101.86%, respectively. As per the International Council for Harmonization Q2 (R1) guideline, the proposed TLC method was repeatable and selective as per statistical analysis and it can be used for simultaneous estimation of Bisoprolol fumarate and Ivabradine HCl in bulk and formulation.

Synthesis and simple method of characterization of aldehyde-silica gel

Abstract: Two approaches to the functionalization of the silica gel surface have been proposed, which make it possible to obtain materials with covalently immobilized highly reactive aldehyde groups. Immobilization of aldehyde groups in the first case is achieved by the click-reaction of azido-alkyne cycloaddition of 4-(prop-2-in-1-yloxy)benzaldehyde and 3-azidopropyl silica gel. In the second case, surface modification is performed by the alkylation reaction of hydroxybenzaldehydes with 3-chloropropyl silica gel. The obtained silica gel samples were characterized by infrared spectroscopy and thermogravimetric analysis data. In IR spectra absorption bands determination of aldehyde groups on the silica gel surface using 2.4 -dinitrophenylhydrazine has been proposed. The proposed method is based on the condensation reaction between the aldehyde groups grafted on the surface and 2.4 -dinitrophenylhydrazine. The quantitative estimation of the grafted aldehyde groups is suggested to be calculated by the difference between the initial amount of 2.4-dinitrophenylhydrazine and the amount remaining in the solution after the reaction. The necessity of maintaining a constant acidity of the medium by adding H2SO4 was established. It is shown that at λ = 315 nm the Bouguer-Beer-Lambert Law is satisfied in the concentration range 2.5∙10-5 to 12.5∙10-5 M. The correctness of the proposed method was checked using the procedure of operative control of the correctness of the results of chemical analysis. This procedure provides the determination of aldehyde groups in the modified material by multiply varying the silica gel weight and using the root-mean-square deviation of the repeatability of measurement results as an error characteristic. The proposed method for determining the aldehyde groups was tested on all silica gel samples. It was shown that by varying the conditions of surface modification it is possible to obtain materials with different functional capacity for aldehyde groups.

Modified Column Lamography Silicone Powder Separates Thiophene and its Derivatives

Abstract: Abstract Column laminating silica gel board plays a very important role in the separation and analysis of organic synthesis, which can monitor the progress of chemical reactions in real time and help researchers determine the time when chemical reactions are completed. In this work, we made a modified silicone powder for the separation and analysis of thiophene substances, and found that the modified silicone powder has a better separation effect than commercial silicone powder, which is expected to play a better role in the field of column chromatography separation.