Aminopropyl Silica Gel Research Articles

Immobilization of calix[6]arene bearing carboxylic acid and amide groups on aminopropyl silica gel and its sorption properties for Cr(VI)

An aminopropyl silica gel-immobilized calix[6]arene (C[6]APS) containing both amide and acid moieties was prepared from p-tert-butylcalix[6]arene hexacarboxylate derivative and aminopropyl silica gel in the presence of N,N′-diisopropyl carbodiimide coupling reagent. C[6]APS was used to evaluate the sorption properties of Cr(VI) as a sorbent material. In sorption studies, it was observed that C[6]APS was highly effective at pH 1.5 for Cr(VI). The effect of parameters such as pH, sorbent dosage, contact time, initial Cr(VI) concentration and temperature on Cr(VI) sorption; the sorption isotherms were also studied. Maximum sorption capacity was obtained as 3.1 mg g−1 at pH 1.5 and 25 °C for 1 h and 10.4 mg L−1 initial Cr(VI) concentration. Thermodynamic parameters such as change in free energy, enthalpy, and entropy were also determined. In the isotherm studies, Langmuir and Freundlich isotherm models were applied and it was found that the experimental data confirmed to Freundlich isotherm model, and the batch sorption capacity of C[6]APS was calculated as 37.66 mg g−1.

Synthesis and electron paramagnetic resonance study of a nitroxide free radical covalently bonded on aminopropyl-silica gel

A solid spin-labeled material was obtained starting from 2-chloro-3,5-dinitro- N-(4-(2,2,6,6-tetramethyl-piperidine-1-oxyl)-benzamide) and aminopropyl-silica gel. Stability tests showed that even after several months the spin-labeled material had the same properties as immediately after synthesis. EPR properties of the TEMPO-derivatized silica were studied as a function of solvent polarity and temperature. Rotational correlation times were calculated from EPR spectra and correlated with solvent characteristics and temperature. Polar solvents induce a fast motion of the spin-label, clearly seen in the EPR spectra by the apparition of the well-known TEMPO radical triplet. The solid spin-labeled (dry) sample showed a high interspin interaction, which can be disrupted not only by different (liquid) solvents, but also by absorption of different solids, like cyclodextrins, dendrimers or polyethyleneglycols. Also, changes induced by the temperature were studied in the case of toluene wet sample. From 150 to 370 K, the spectrum is changing from a slow motion spectrum type to a fast motion regime. The preparative procedures to obtain the spin-labeled silica as well as some of its parameters are described.

Preparation of a new chiral stationary phase for HPLC based on the (R)‐ 1‐phenyl‐2‐(4‐methylphenyl)ethylamine amide derivative of (S)‐valine and 2‐chloro‐3,5‐dinitrobenzoic acid: Enantioseparation of amino acid derivatives and pyrethroid insecticides

A novel chiral stationary phase (CSP) for HPLC was prepared by bonding (R)-1-phenyl-2-(4-methylphenyl)ethylamine amide derivative of (S)-valine to aminopropyl silica gel through a 2-amino-3,5-dinitro-1-carboxamido-benzene unit. The CSP was used for the separation of some amino acid derivatives and pyrethroid insecticides by chiral HPLC. Satisfactory baseline separation required optimization of the variables of mobile phase composition. Use of dichloromethane as modifier in the mobile phase gave baseline separations of amino acid derivatives. The two enantiomers of fenpropathrin and four stereoisomers of fenvalerate were baseline separated using hexane-dichloromethane-ethanol as mobile phase. The results show that the enantioselectivity of the new CSP is better than Pirkle type 1-A column for these compounds. Only partial separations were observed for the stereoisomers of cypermethrin and cyfluthrin, which gave even and eight peaks, respectively.

Evaluation of the Temperature Responsive Stationary Phase Poly(N-isopropylacrylamide) in Aqueous LC for the Analysis of Small Molecules

Liquid chromatography columns were packed with a temperature responsive stationary phase based on poly(N-isopropylacrylamide) (PNIPAAm) attached to aminopropyl silicagel. This polymer shows hydrophilic properties below 32 °C and becomes hydrophobic above that temperature. The temperature responsive properties of the coupled phase are demonstrated using only water as mobile phase, whereby an increase in retention is observed with raising temperature. Mixtures of compounds covering a wide polarity range and including phenones, alkylbenzenes, phenols, alkylated benzoic acids, anilines, sulfonamides and carbamates were analyzed and the retention, peak shapes and plate counts were compared under identical conditions. For retained solutes, an increase in retention as a function of the temperature between 25 and 55 °C could be noted, whereby this was higher for the analytes containing a longer hydrophobic chain. Compounds with similar hydrophobic chains, but containing additional polar functions showed increased retention and improved peak shapes, suggesting a mixed mode interaction mechanism also at temperatures well above the transition temperature of the polymer. Weak acids and bases could be analyzed by pH adjustment. This is demonstrated for mixtures of benzoic acid derivatives and sulfamide drugs. A carbamate pesticide mixture was analyzed at 55 °C with water (pH 5.5) as mobile phase and ESI-MS detection. Temperature responsive stationary phases open perspectives for green chromatography.

Enantioselective and diastereoselective separation of synthetic pyrethroid insecticides on a novel chiral stationary phase by high‐performance liquid chromatography

A novel chiral packing material for high-performance liquid chromatography (HPLC) was prepared by connecting (R)-1-phenyl-2-(4-methylphenyl) ethylamine (PTE) amide derivative of (S)-isoleucine to aminopropyl silica gel through 2-amino-3,5-dinitro-1-carboxamido-benzene unit. This chiral stationary phase was applied to the enantioselective and diastereoselective separation of five pyrethroid insecticides by HPLC under normal phase condition. To achieve satisfactory baseline separation an optimization of the variables of mobile phase composition was required. The two enantiomers of fenpropathrin and four stereoisomers of fenvalerate were baseline separated using hexane-1,2-dichloroethane-2-propanol as mobile phase. The results show that the enantioselectivity of CSP is better than Pirkle type 1-A column for these compounds. Only partial separations for the cypermethrin and cyfluthrin stereoisomers were observed. Seven peaks and eight peaks were observed for cypermethrin and cyfluthrin, respectively. The elution orders were assigned by using different stereoisomer-enriched products.

Simultaneous Determination of Neonicotinoid Insecticides in Agricultural Samples by Solid-Phase Extraction Cleanup and Liquid Chromatography Equipped with Diode-Array Detection

Effective sample pretreatment procedures based on solid-phase extraction (SPE) for multiresidue determination of seven neonicotinoid insecticides in agricultural products were investigated. After extraction with acetone and concentration, the insecticides in aqueous sample extracts were transferred into organic solvent phases with a Chem Elut SPE cartridge. Finally, the eluate from the cartridge was cleaned up with a SPE cartridge packed with graphitized carbon black and aminopropyl silica gel, which showed a higher cleanup efficiency than the classical silica gel SPE cartridge. Seven insecticides were separated on a reversed-phase C18 column and a gradient system of methanol and phosphate solution based on high-performance liquid chromatography. The established multiresidue determination has been applied to several artificially spiked agricultural samples, with the result that the average recoveries were excellent, with the exception of nitenpyram. The limit of detection of the method ranged from 0.01 to 0.03 mg/kg for the insecticides.

Solid-phase extraction of trace Cu(II) Fe(III) and Zn(II) with silica gel modified with curcumin from biological and natural water samples by ICP-OES

Silica gel was firstly functionalized with aminopropyltrimethoxysilane obtaining the aminopropylsilica gel (APSG). The APSG was reacted subsequently with curcumin yielding curcumin-bonded silica gel (curcumin-APSG). This new bonded silica gel was used for separation, pre-concentration and determination of Cu(II), Fe(III), Zn(II) in biological and natural water samples by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions for effective adsorption of trace levels of metal ions were optimized with respect to different experimental parameters using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the newly sorbent was 4.0. Complete elution of the adsorbed metal ions from the sorbent surface was carried out using 2.0 mL of 0.1 mol L − 1 of HCl. Common coexisting ions did not interfere with the separation and determination at pH 4.0. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 0.63, 0.46 and 0.37 mmol g − 1 for Cu(II), Fe(III) and Zn(II) respectively. The time for 95% sorption for Cu(II) Fe(III) and Zn(II) was less than 2 min. The detection limits of the method defined by IUPAC was found to be 0.12, 0.15 and 0.40 ng mL − 1 for Cu(II), Fe(III) and Zn(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was lower 3.0% ( n = 5). The procedure was validated by analyzing the certified reference river sediment material (GBW 08301, China), the results obtained were in good agreement with standard values. This sorbent was successfully employed in the separation and pre-concentration of trace Cu(II), Fe(III) and Zn(II) from the biological and natural water samples yielding 75-fold concentration factor.

Studies of compounds that enhance sphingolipid metabolism in human keratinocytes1

Several products are known to inhibit the biosynthesis of ceramides and glucosylceramides, but very few stimulate this process. We studied the influence of a hydrolysate of potato proteins (Lipidessence) in vitro on the sphingolipid metabolism of normal human epidermal keratinocytes. By measuring growth with the thymidine uptake assay, it was seen that Lipidessence, added in the culture medium up to an 8% concentration, did not change significantly the proliferation rate of keratinocytes, but beyond this concentration a progressive dose-dependent inhibition of growth was noticeable. Following incubation of cells with the product at 5% and 10% concentrations for 2 days, the lipids were extracted. The different lipid classes were separated by fractionation on columns of aminopropyl silica gel and analyzed by high-performance thin-layer chromatography. When keratinocytes were cultivated in the presence of Lipidessence, the biosynthesis of cholesterol, phosphatidylcholine, phosphatidylserine and gangliosides was stimulated, and a major increase was noticeable in the biosynthesis of free fatty acids, free ceramides, glucosylceramide and sphingomyelin. Radioactive [(14)C]-serine was used as a precursor of sphingoid bases to study sphingolipid biosynthesis. After migration of lipid fractions on thin-layer plates, autoradiography showed that free ceramides and glucosylceramide were labeled, thus suggesting that de novo biosynthesis was accounting for the increased cellular content in sphingolipids.

HPLC Retention Behaviors of Poly-aromatic-hydrocarbones on Cu(II)-octabromotetrakis(4-carboxyphenyl)porphine Derivatives-Immobilized Aminopropyl Silica Gels in Polar and Non-Polar Eluents

As one of approaches of developing novel HPLC stationary phases, we prepared Cu-octabromotetrakis(4-carboxyphenyl)porphine derivative-immobilized silica gels (Cu-OBTCPP(D)), and evaluated the availability of the resultant Cu-OBTCPP(D) as a stationary phase for separation of poly-aromatic-hydrocarbons (PAHs) and their related compounds. A Cu-OBTCPP(D) column was revealed to have an ability to separate simple PAHs and be useful as a stationary phase in both polar and non-polar eluents. The retention property of the Cu-OBTCPP(D) column was evaluated in various comparative experiments using commercially available columns. In comparison with 2-(1-pyrenyl)ethyl dimetylsilyl silica gel column (PYE column) regarding the retention behavior for PAHs etc., the Cu-OBTCPP(D) column showed stronger interactions involving pi electron in non-polar eluent than PYE column. In comparison with a pentabromobenzyloxy propylsilyl silica gel column (PBB column) regarding the influence of bromination, the Cu-OBTCPP(D) column was affected differently from the PBB column. In comparison with nitrophenylethyl silica gel column (NPE column) regarding the retention behavior for compounds having a dipole in a non-polar eluent, the Cu-OBTCPP(D) column showed electrostatic interactions such as dipole-dipole interaction equivalent to or larger than the NPE column.

Synthesis and characterisation of morin-functionalised silica gel for the enrichment of some precious metal ions

Silica gel was firstly functionalised with aminopropyltrimethoxysilane obtaining the aminopropylsilica gel (APSG). The APSG was reacted subsequently with morin yielding morin-bonded silica gel (morin-APSG). The structure was investigated and confirmed by elemental and thermogravimetric analyses, IR and 13C NMR spectral studies. Morin-APSG was found to be highly stable in common organic solvents, acidic medium (<2 mol L −1 HCl, HNO 3) or alkaline medium up to pH 8. The separation and preconcentration of Ag(I), Au(III), Pd(II), Pt(II) and Rh(III) from aqueous medium using morin-APSG was studied. The optimum pH values for the separation of Ag(I), Au(III), Pd(II), Pt(II) and Rh(III) on the sorbent are 5.7, 2.2, 3.7, 3.7 and 6.8, giving rise to separation efficiencies of 43.9, 85.9, 97.7, 60.9 and 91.0%, respectively, where the activity was found to be >90% in the presence of acetate ion. The ion sorption capacity of morin-APSG towards Cu(II) at pH 5.5 was found to be 0.249 mmol g −1 where the sorption capacities of Ag(I) and Pd(II) were 0.087 and 0.121 mmol g −1 and 0.222 and 0.241 mmol g −1 at pH 2.2 and 5.7, respectively. This indicates a 1:1 and 1:2 morin/metal ratios at pH 2.2 and 5.7, respectively. Complete elution of the sorbed metal ions was carried out using 10 mL (0.5 mol L −1 HCl + 0.01 mol L −1 thiourea) in case of Au(III), Pd(II), Pt(II) and Rh(III) and 10 mL 0.5 mol L −1 HNO 3 in case of Ag(I). Morin-APSG was successfully employed in the separation and preconcentration of the investigated precious metal ions from some spiking water samples yielding 100-folds concentration factor. The relative standard deviation (R.S.D.) and the T-test ( | t | 1 ) were calculated.

Sorption Behavior of Vanadium on Silica Gel Modified with Tetrakis(4-carboxyphenyl)porphyrin

Tetrakis(4-carboxyphenyl)porphyrin (TCPP) has been loaded on aminopropyl-silica gel by physical adsorption and by direct immobilization through formation of an amide bond to obtain chelating sorbents. These sorbents have been studied for preconcentration and separation of vanadium prior to its determination by atomic absorption spectrometry. Several parameters, such as sorption capacity of the chelating resin, pH for retention of V(IV) and V(V), volume of sample and eluent, were evaluated. Both vanadium species sorbed on TCPP-modified resin could be eluted using 2 mol L(-1) nitric acid solution. The recovery values were > 94% and preconcentration factor of 160 was obtained. For speciation analysis, cyclohexane-1,2-diaminetetraacetic acid (CDTA) was added to the sample for complexation of vanadium(IV), which was not retained on the microcolumn. The proposed method was examined for reference standard materials (TM-25.2 and CAAS-3) as well as for river water samples.

Catechol functionalized aminopropyl silica gel: synthesis, characterization and preconcentrative separation of uranium(VI) from thorium(IV)

Summary A novel solid phase extractant is prepared by chemically immobilizing catechol with diazotized aminopropyl silica gel. The resulting catechol functionalized silica gel (CASG) was characterized by FTIR, and microanalysis and was used for selective enrichment of uranium(VI) from other inorganic ions. The optimum pH range for maximum sorption of uranium(VI) and thorium(IV) was found to be in the range 3.5–6.0. The above actinides were eluted with 10 cm3 of 1.0 mol dm−3 HCl and determined by using an Arsenazo III spectrophotometric procedure. The calibration graph was rectilinear over the uranium(VI) concentration in the range 2–100 μg dm−3 with a relative standard deviation of 2.15% (for 25 μg of uranium(VI) present in 1.0 dm3 of sample). The validation of the developed preconcentration procedure was carried out by analyzing marine sediment (MESS-3, NRC, Canada) and soil (IAEA soil-7, Austria) reference materials. The developed preconcentration method enables a simple instruments like a spectrophotometer gave comparable values of uranium(VI) to that of standard inductively coupled plasma-mass spectrometric values during the analysis of real soil and sediment samples.

Influence of spacers and organic modifiers on chromatographic behaviors on chiral diamide stationary phase with N-(3,5-dimethylbenzoyl)- d-phenylglycine

A chiral diamide stationary phase (CSP) with different length of spacers has been synthesized by chemically bonding the N-(3,5-dimethylbenzoyl)- d-phenylglycine on the aminopropylsilica gel or silica gel bonded with different carbon chain length of spacers. These CSPs have successfully been used for the chiral resolutions of the benzoyl- dl-octylamine and benzoyl- dl-amino acid isopropyl esters in normal-phase liquid chromatography (NP-LC). The spacer length and the introduction of a secondary amine group in the CSPs have been investigated. It has been found that a long spacer of CSPs generally benefits on the enantioselectivity. The introduction of secondary amine group in the spacer leads to the decline of separation factors. Further, the effect of organic modifiers has been examined. Proper use of organic modifiers resulted in an interesting ‘masking effect’ on the residing silanol groups of the CSPs. The addition of suitable amount of organic modifiers improves the enantioselectivity, and enantioselectivity depends on the shape of organic modifiers in the mobile phases.

Organically modified silica gel and flame atomic absorption spectrometry: employment for separation and preconcentration of nine trace heavy metals for their determination in natural aqueous systems

A 5-formyl-3-(1′-carboxyphenylazo) salicylic acid-bonded silica gel (FCPASASG) chelating adsorbent was synthesized according to a very simple and rapid one step reaction between aminopropyl silica gel (APSG) and 5-formyl-3-(1′-carboxyphenylazo) salicylic acid (FCPASA) and its adsorption characteristics were studied in details. Nine trace metals viz.: Cd(II), Zn(II), Fe(III), Cu(II), Pb(II), Mn(II), Cr(III), Co(II) and Ni(II) can be quantitatively adsorbed by the adsorbent from natural aqueous systems at pH 7.0–8.0. The adsorbed metal ions can be readily desorbed with 1 M HNO 3 or 0.05 M Na 2EDTA. The distribution coefficient, K d and the percentage concentration of the investigated metal ions on the adsorbent at equilibrium, C M, eqm % (Recovery, R%) were studied as a function of experimental parameters. The logarithmic values of the distribution coefficient, log K d, are 3.7–6.4. Some foreign ions caused little interference in the preconcentration and determination of the investigated nine metals by flame atomic absorption spectrometry (AAS).The adsorption capacity of FCPASASG was 0.32–0.43 meq g −1. C and N elemental analyses of the adsorbent (FCPASASG) allowed us to calculate a surface converge of 0.82 mmol g −1. This value compares well with the best values reported for the azo compounds. The adsorbent and its formed metal chelates were characterized by IR (absorbance and/or reflectance) and UV spectrometry, potentiometric titrations and thermogravimetric analysis (TGA and DTG). The mode of chelation between the FCPASASG adsorbent and the investigated metal ions is proposed to be due to reaction of those metal ions with the salicylic and/or the carboxyphenylazo chelation centers of the FCPASASG adsorbent. Nanogram concentrations (0.07–0.14 ng ml −1) of Cd(II), Zn(II), Fe(III), Pb(II), Cr(III), Mn(II), Cu(II), Co(II) and Ni(II) can be determined reliably with a preconcentration factor of 100.

Stationary phases with special structural properties for high-throughput separation techniques: preparation, characterization and applications.

Stationary phases with specific structural properties for high-throughput liquid chromatographic (LC) techniques are described. Special attention was paid to phases with special structural properties, mainly containing internal functional group (e.g. amide). Such materials are generally called "embedded phases". There are phases created in amidation process of aminopropylated silica gel, especially phases based on biological compounds, like phospholipids and cholesterol, which are called immobilized artificial membranes (IAM's). The synthesis and applications of polar embedded amide LC stationary phases were also reviewed. Methods of characterization of synthesized packing materials were presented, with general focusing on spectroscopic measurements like (13C and 29Si CP/MAS NMR and FT-IR), elemental and thermal analysis as well as chromatographic quantitative structure-retention relationships (QSRR) and extended chemometric tests. The potential applications of various dedicated stationary phases in a high-throughput LC screening procedures were also presented.

Silica Gel Loaded with o -Dihydroxybenzene: Design, Metal Sorption Equilibrium Studies and Application to Metal Enrichment Prior to Determination by Flame Atomic Absorption Spectrometry

The aminopropyl silica gel (APSG) prepared by reaction of activated silica gel with 3-aminopropyltriethoxysilane on reaction with 3,4-dihydroxybenzaldehyde has resulted in a new chelating matrix, o-dihydroxybenzene (DHB) anchored silica gel, which is characterized by IR, TGA and elemental analyses. APSG is characterized with 13C CPMAS NMR spectroscopy. DHB anchored silica gel sorbs quantitatively (97.4–99.2% recovery) Cu(II), Pb(II), Fe(III), Zn(II), Co(II), Ni(II) and Cd(II) at pH 6.0–7.5, 5.0–7.0, 5.5–7.0, 6.0–8.0, 6.5–8.0, 5.5–7.0 and 6.5–7.5, respectively. The sorption capacity varies from 32 to 348 µmol g−1 and is highest for copper. Desorption was found to be quantitative with 1.0–3.0 mol L−1 HCl/HNO3 (for Pb). The optimum flow rate of the solution for quantitative sorption of metal ions on a column (10 cm × 10 mm) packed with 1 g of the modified silica gel is 1.0–4.0 mL min−1, whereas for desorption it is 2.0 −4.0 mL min−1. The tolerance limits for NaCl, NaBr, NaI, NaNO3, Na2SO4, Na3PO4, humic acid, EDTA, ascorbic acid, citric acid, sodium tartrate, Ca(II) and Mg(II) in the sorption of all the seven metal ions are reported. The preconcentration factors are between 100 and 300 and t1/2 values ≤17 min. The present matrix coupled with FAAS has been used to enrich and determine the seven metal ions in river and tap water samples (RSD 1.4–7.0%) and in synthetic certified water samples SLRS-4 (NRC, Canada) with an RSD of 2.73–2.83%. The cobalt present in pharmaceutical vitamin tablets and Zn in milk powder was preconcentrated on DHB anchored silica gel and determined by FAAS (RSD of 2.00 to 2.72%).

A new diamide‐type chiral stationary phase for chiral resolution by normal and reversed phase HPLC

In this work, a new diamide‐type chiral stationary phase was developed by chemically bonding the N‐stearoyl‐L‐leucine on the aminopropylsilica gel. It has been successfully used for the chiral resolution of the benzoyl‐, dinitrobenzoyl‐, and trifluoroacethyl amino acids in the modes of normal phase, as well as for the underivatized amino acids in the mode of reversed phase. It was found that the hydrogen bonding makes significant contribution to the chiral resolution. It has been demonstrated that the chiral resolution, by the use of diamide‐type chiral stationary phase (CSP), can be achieved without the π–π interaction between the CSP and analytes.

Separation of the enantiomers of tebuconazole and its potential impurities by high-performance liquid chromatography with a cellulose derivative-based chiral stationary phase

The high-performance liquid chromatographic resolution of the enantiomers of tebuconazole, a new anti-fungal agent with one chiral center, and the enantiomers of some impurities in technical tebuconazole, has been studied on a chiral stationary phase prepared by coating aminopropylated silica gel with celluloseris(3,5-dimethylphenylcarbamate). The effects of solute structure and the amount of the organic mobile-phase modifier, 2-propanol, on retention and resolution were studied. Under optimum conditions excellent enantiomer separations were achieved for tebuconazole and its impurities. As far as we are aware this is the only liquid chromatographic system enabling discrimination of the enantiomers of all of the racemates discussed in this paper.

Enantiomer Separation and Molecular Recognition with New Chiral Stationary Phases on 4‐Chloro‐3,5‐dinitrobenzoic Acid Amides of α,β‐Aminoalcohols and α‐Arylethylamines

Amides of 4‐chloro‐3,5‐dinitrobenzoic acid (1) (CDNB) with enantiomerically pure α,β‐aminoalcohols (2–5) and α‐substituted ethylamines,6–9 have been prepared as chiral selectors 10–17 and bound to aminopropyl silica gel affording chiral stationary phases CSPs 1–8. Comparative tests of their separation efficacy for 32 racemic analytes, representative of racemates with selected functionalities, has revealed important contribution of the π‐acidic branching unit, the amide of 3,5‐dinitro‐4‐alkylaminobenzoic acid, but limited contribution of both, hydrophilic hydroxy groups in the CSPs 1–4 and π‐basic aromatic units in the CSPs 6–8. Contribution to enantioselection efficacy of the γ‐aminopropyl groups on the silica surface, in the vicinity to the chiral selector, is documented comparing the efficacy of CSP 8 and CSP 8′.

ChemInform Abstract: Aminopropyl Silica Gel Supported Iodine as Catalyst in Nucleophilic Ring Opening of Epoxides and Episulfides.

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