Silica Gel Beads Research Articles

Development of a single fluorescence-based optosensor for rapid simultaneous determination of fungicides benomyl and thiabendazole in waters and commercial formulations.

A novel, sensitive, and straightforward spectrofluorimetric flow injection method is proposed in this work for the resolution of a binary mixture of two widely used fungicides (thiabendazole and benomyl). The continuous flow methodology is based on the implementation of on-line solid phase extraction (SPE), preconcentration, and separation of both analytes on a surface of C(18) silica gel beads placed just in the flow cell, with solid surface fluorescence detection. A 45- and 25-fold sensitivity enhancement was obtained for benomyl and thiabendazole, respectively (in relation to the liquid phase measurements in the absence of solid support). The separation of the pesticides was performed because of the different retention-desorption kinetics in their interaction with the solid support, in the zone where the stream impinges the solid material. No previous separation of the analytes before they reach the flow cell is needed, simplifying extraordinarily both the procedure and the manifold. Using a sample volume of 3200 microL, the system was calibrated in the range of 0.4-20 and 20-400 ng x mL(-)(1) with detection limits of 0.06 and 3.6 ng x mL(-)(1) for thiabendazole and benomyl, respectively, and RSD values (n = 10) smaller than 0.8% for both analytes. The RSD values obtained replacing the solid support in each measurement were lower than 3%, and the day-to-day reproducibility RSD value was also lower than 5%. Sampling frequencies of 10 and 18 h(-)(1) were obtained with 600 and 3200 microL of sample volume. Recovery studies carried out on natural water samples spiked with known amounts of both analytes at concentration levels in the range of 1-10 and 25-200 ng x mL(-)(1) provided mean recovery percentages ranging from 98.8 to 102% and from 98 to 103% for thiabendazole and benomyl, respectively. The proposed methodology was also applied to pesticide formulations.

Tritium Isotope Separation by Water Distillation Column Packed with Silica-gel Beads

Tritium Isotope Separation by Water Distillation Column Packed with Silica-gel Beads

Drying of Porous Materials in Fluidized Bed of Silica Gel Beads

Drying of Porous Materials in Fluidized Bed of Silica Gel Beads

Continuous-flow separation and pre-concentration coupled on-line to solid-surface fluorescence spectroscopy for the simultaneous determination of o -phenylphenol and thiabendazole

A novel and single flow-injection system combined with solid-surface fluorescence detection is proposed in this work for the resolution of a mixture of two widely used pesticides (o-phenylphenol and thiabendazole). The continuous-flow methodology is based on the implementation of on-line pre-concentration and separation of both analytes on the surface of C18 silica gel beads placed just inside the flow cell, implemented with gel-phase fluorimetric multi-wavelength detection (using 305/358 and 250/345 nm as excitation/emission wavelengths for thiabendazole and o-phenylphenol, respectively). The separation of the pesticides was possible owing to the different retention/desorption kinetics of their interactions with the solid support in the zone where the stream impinges on the solid material. No previous separation of the analytes before they reach the flow cell is needed thereby simplifying substantially both the procedure and the manifold. By using a sample volume of 2,600 microL, the system was calibrated in the range 0.5-16 and 5-120 ng mL(-1) with detection limits of 0.09 and 0.60 ng mL(-1) for thiabendazole and o-phenylphenol, respectively. The RSD values (n=10) were about 1% for both analytes. The proposed methodology was applied to environmental water samples and also to various commercial pesticide formulations containing both analytes. Recovery percentages were 97-103% and 98-102% for thiabendazole and o-phenylphenol, respectively.

Surface grafting of glycidyl methacrylate on silica gel and polyethylene beads.

Surface grafting of glycidyl methacrylate (GMA) on silica gel and a polyethylene bead was performed by radical polymerization and radiation-induced polymerization, respectively, in order to improve softness. Subsequently, diethylene triamine (DETA), triethylene tetraamine (TETA), and iminodiacetic acid (IDA) were introduced to the grafted GMA for use as affinity columns. The efficiency of the affinity column was investigated by use of bovine serum albumin (BSA) and hemoglobin (Hb) as model proteins. The affinity degree of BSA was higher than Hb for the DETA and TETA column, whereas the affinity degree of Hb was higher than BSA for the IDA column supported by silica gel. The affinity degree of BSA was higher than Hb for the DETA and TTA column supported by polyethylene (PE) beads.

Solid-phase iodine as an oxidant in flow injection analysis: determination of ascorbic acid in pharmaceuticals and foods by background correction

A flow injection analysis (FIA)-background correction method comprising two solid-phase reactors and spectrophotometry for determination of ascorbic acid (AsA) is proposed. A polyethylene mini-column filled with solid iodine (30% m/m suspended on silica gel beads), reactor 1, and other column filled only with silica gel, reactor 2, which are then incorporated in a flow system so that solid iodine reagent in reactor 1 is affected as the sample passes through the column. The sample blank is produced by the oxidation of the AsA by iodine to form dehydroascorbic acid, insensitive to ultraviolet at 267 nm. AsA in samples is determined after injected in reactor 2; the difference in two analytical signal observed is related to amount of AsA. The linear range of the system is up to 50 μg ml −1 with a detection limit of 0.08 μg ml −1, R.S.D. of better than 1.0% and sampling frequency of 110 sample h −1. The method is successfully applied to the determination of AsA in pharmaceuticals and foods.

The binding of tyrosine hydroxylase to negatively charged lipid bilayers involves the N-terminal region of the enzyme

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of catecholamines. We have studied the association of recombinant human TH with model membranes by using either liposomes or silica gel beads coated with single phospholipid bilayers (TRANSIL ®). The use of TRANSIL beads has allowed the determination of apparent dissociation constants ( K d) for the binding of the enzyme to negatively charged bilayers ( K d=230–380 μM, at pH 6.0–7.0). Binding to the bilayers is accompanied by a decrease in enzyme activity. Proteolysed forms of the enzyme show decreased binding affinity and two putative amphipathic N-terminal α-helices are proposed to be involved in membrane binding. As seen by circular dichroism, binding to the bilayer does not seem to induce significant changes on the secondary structure content of the enzyme, but α-helical structures appear to be stabilized against thermal denaturation in the membrane-bound state. Thus, amphitropism, a mechanism that regulates the function of peripheral proteins by weak binding to membrane lipids, may add to the factors that regulate both the activity and the stability of TH.

Simultaneous separation of common mono- and divalent cations on an acid-treated silica gel column by ion chromatography with indirect photometric detection and tyramine–oxalic acid, containing 18-crown-6 as eluent

The application of unmodified silica gel (Super Micro Bead Silica Gel B-5, SMBSG B-5) as cation-exchange stationary phase in ion chromatography with indirect photometric detection for common mono- and divalent cations (Li +, Na +, NH 4 +, K +, Mg 2+ and Ca 2+) was carried out using 0.75 m M tyramine [4-(2-aminoethyl)phenol]–0.25 m M oxalic acid at pH 5.0 as the eluent. Although complete group separation between these mono- and divalent cations was achieved on the SMBSG B-5 column (150×4.6 mm I.D.) in 12 min, peak shapes of NH 4 + and K + were strongly tailed. Hence, the application of SMBSG B-5 silica gel treated with conc. hydrochloric acid at reflux-temperature for 12 h for the simultaneous separation of these cations was carried out. Although the retention volumes of these cations decreased on the acid-treated SMBSG B-5 silica gel column, the peak shapes of NH 4 + and K + were quite improved. Excellent simultaneous separation and highly sensitive detection at 275 nm [detection limits (signal-to-noise ratio of 3 and injection volume of 20 μl), 0.34 μ M for Li +, 0.47 μ M for Na +, 0.39 μ M for NH 4 +, 0.59 μ M for K +, 0.24 μ M for Mg 2+ and 0.28 μ M for Ca 2+] were achieved in 15 min on the acid-treated SMBSG B-5 column using 0.5 m M tyramine–0.2 m M oxalic acid–10 m M 18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) at pH 5.5 as the eluent.

Retention behavior of common mono- and divalent cations on calcinated silica gel columns in ion chromatography with conductimetric detection and the use of nitric acid, containing crown ethers, as eluents

Ion chromatographic behavior of common mono- and divalent cations (Li +, Na +, NH 4 +, K +, Mg 2+ and Ca 2+) on columns packed with silica gels (Super Micro Bead Silica Gel B-5, SMBSG B-5) calcinated at 200, 400, 600, 800 and 1000 °C for 5 h was investigated using nitric acid containing crown ethers [18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) and 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)] as eluent. When using 0.5 m M HNO 3 as the eluent, the calcination had almost no effect on the improvement of peak resolution between these mono- and divalent cations. In contrast, when using 0.5 m M HNO 3 containing crown ethers as the eluent, with increasing the calcinating temperature, the amount of crown ethers adsorbed on the corresponding calcinated SMBSG B-5 silica gels columns increased and, as a consequence, peak resolution between these mono- and divalent cations was quite improved. Excellent simultaneous separation of these mono- and divalent cations was achieved on column (150×4.6 mm I.D.) packed with the SMBSG B-5 silica gel calcinated at 1000 °C by elution with 0.5 m M HNO 3 containing either 1.0 m M 18-crown-6 or 5.0 m M 15-crown-5.

Simultaneous separation of common mono- and divalent cations on a calcinated silica gel column by ion chromatography with indirect photometric detection and aromatic monoamines–oxalic acid, containing crown ethers, used as eluent

The application of unmodified silica gel (Super Micro Bead Silica Gel B-5, SMBSG B-5) as a cation-exchange stationary phase in ion chromatography with indirect photometric detection (IC–IPD) for the separation of common mono- and divalent cations (Li +, Na +, NH 4 +, K +, Mg 2+ and Ca 2+) was carried out using various aromatic monoamines {tyramine [4-(2-aminoethyl)phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine} as eluents. When using these amines as eluents, the peak resolution between these mono- and divalent cations was not quite satisfactory and the peak shapes of NH 4 + and K + were largely destroyed on the SMBSG B-5 silica gel column. Hence, the application of SMBSG B-5 silica gel calcinated at 200, 400, 600, 800 and 1000 °C for 5 h in the IC–IPD was carried out. The peak shapes of the monovalent cations were greatly improved with increasing calcination temperature and, as a result, symmetrical peaks of these mono- and divalent cations were obtained on the SMBSG B-5 silica gel calcinated at 1000 °C as the stationary phase. In contrast, the peak resolution between these mono- and divalent cations was not improved. Therefore, crown ethers [18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)] were added to the eluent for the complete separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection at 275 nm were achieved in 25 min on a column (150×4.6 mm I.D.) packed with SMBSG B-5 silica gel calcinated at 1000 °C by elution with 0.75 m M tyramine–0.25 m M oxalic acid at pH 5.0 containing either 1.0 m M 18-crown-6 or 10 m M 15-crown-5.

UV SPECTROPHOTOMETRIC FLOW-THROUGH MULTIPARAMETER SENSOR FOR THE SIMULTANEOUS DETERMINATION OF ACETAMINOPHEN, ACETYLSALICYLIC ACID, AND CAFFEINE

ABSTRACT A single triparameter flow-through sensor with U.V. detection is described in this study for the simultaneous determination of acetaminophen, acetylsalicylic acid and caffeine. The use of an solid phase (C18 silica gel) placed in an on-line microcolumn provides the sequential arrival of the analytes to the detection solid zone (also C18 silica gel beads placed in a flow cell), making possible the determination with only one injection. A flow rate of 1.42 mL min−1 was pumped and detection wavelength was 272 nm. The linear dynamic ranges were 10–100, 40–500 and 4–50 µg mL−1, for acetaminophen, acetylsalicylic acid and caffeine, respectively. Limit of detection were from 0.3 to 0.8 µg mL−1 and limit of quantitation were from 1.0 and 2.7 µg mL−1 with RSDs from 1.2 to 3.4 (n = 10), respectively. The proposed method was applied to the determination of acetaminophen, acetylsalicylic acid and caffeine in pharmaceutical preparations. The results were compared with those obtained from an HPLC method and they showed a good agreement.

The pH-detection of triglycerides

This paper presents an indirect method of triglycerides determination based on pH-detection. The system consisted of a microreactor containing silica gel beads with surface immobilised lipase and the pH-sensor of ISFET type. Three methods of lipase immobilisation: (1) the chemical bond to the surface of glass beads coated with keratin, (2) entrapment within alginate gel beads and (3) adsorption onto nitrocellulose sheets were compared. All methods of lipase immobilisation, except the second one, were found to be effective. The systems consisting of microreactors packed with surface immobilised lipase were calibrated for different substrates. The highest sensitivity was obtained for tributyrin (0.478 pH/mM for concentration <4 mM), while the widest linear range was obtained for triacetin (up to 30 mM). The results concerning the influence of some factors, such as activators, and emulgators upon the sensor response are also presented.

Solid-phase reactors in sequential injection analysis. Determination of manganese (II) in tap water and effluent streams using a solid-phase lead(IV) dioxide reactor in a sequential injection system.

The determination of manganese(II) in tap water and effluent streams, using a solid-phase reactor incorporated into a sequential injection system was investigated. Mn2+-ions in samples injected into a carrier stream, were oxidised by solid lead(IV) dioxide suspended on silica gel beads to form MnO4- -ions which were detected spectrophotometrically at 526 nm. The linear range of the system is from 1 to 7 mg L(-1) with a detection limit of 0.62 mg L(-1). The proposed system is suitable for the determination of manganese(II) in tap and effluent streams at a rate of approximately 50 samples per hour with a relative standard deviation of better than 3%. Statistical comparison between the proposed sequential injection system and a standard ICP method revealed that there is no significant difference between the two methods at the 95% confidence level for effluent streams and at 99.9% for tap water.

Apatite-Silica Gel Composite Materials Prepared by a New Alternate Soaking Process

Novel apatite/silica composite materials were synthesized by modifying the surface of silica gel beads or plates with apatite. An “alternate soaking” process, which involves alternate soaking in a CaCl2/tris-HCl aqueous solution (pH 7.4) and a Na2HPO4 aqueous solution, was utilized to prepare a composite of silica gel and apatite. The characteristics of apatite formed on the surface of silica gel have been studied using X-ray diffraction, Fourier-transform infrared spectrophotometry (FT-IR) and scanning electron microscopy (SEM). Data clearly showed surface modification of silica with the crystalline apatite. Pore volume and specific total surface area, which were measured using nitrogen gas adsorption apparatus, were decreased after apatite deposition on the surface of silica gel beads, whereas the external surface area was increased drastically. The alternate soaking process made it possible to prepare apatite/silica gel composites in a remarkably short period of time, i.e. several hours.

Solid-phase sodium bismuthate as an oxidant in flow injection analysis: determination of manganese in effluent streams

An alternative procedure for the flow injection spectrophotometric determination of manganese(II) using a solid-phase reactor is presented. Solid sodium bismuthate (50% m/m suspended on silica gel beads) is packed in a polyethylene column, which is then incorporated in a single-line flow system so that reagent dissolution is affected as the sample passes through the column. Mn 2+ in samples injected into a carrier stream were oxidized by solid sodium bismuthate to form MnO 4 − which were detected spectrophotometrically at 526 nm. The linear range of the system is 1–20 mg l −1 with a 3 σ detection limit of 0.38 mg l −1. The proposed system is suitable for determination of manganese(II) in effluent streams with a relative standard deviation <1.35%.

Ion chromatography with indirect photometric detection of common mono- and divalent cations using an unmodified silica gel column and tyramine/oxalic acid/18-crown-6 as eluent

A separation column (150 mm × 4.6 mm i.d.) packed with an unmodified silica gel (Super Micro Bead Silica Gel B-5: SMBSG B-5) was applied to ion chromatography with indirect photometric detection (IC-IPD) for common mono- and divalent cations (Li +, Na +, NH 4 +, K +, Mg 2+ and Ca 2+) using tyramine (4-aminoethylphenol) as eluent. When using 0.5 mM tyramine/0.2 mM oxalic acid at pH 4.75 as the eluent, complete separation of the divalent cations and incomplete separation of the monovalent cations were achieved. On the addition of 3 mM 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) to the eluent, highly sensitive indirect-UV photometric detection at 275 nm and excellent separation for these cations were achieved in 17 min. The proposed IC-IPD was successfully applied to cation analysis in various natural water samples.

Investigation of Mechanisms Contributing to Slow Desorption of Hydrophobic Organic Compounds from Mineral Solids

This research investigates the mechanisms contributing to the slow desorption of hydrophobic organic compounds from water-saturated mineral solids. The mechanisms investigated were adsorption-retarded aqueous diffusion, micropore diffusion, high-energy micropore adsorption, and micropore blockage by precipitated minerals. To reduce the potential confounding effects of adsorbent heterogeneity, a set of homogeneous silica gel and glass bead adsorbents were used in the investigation. Desorption rates for the slow-desorbing fractions of chloroform (CF), trichloroethylene (TCE), and perchloroethylene (PCE) from silica gel did not conform to the pore-diffusion model for adsorption-retarded aqueous diffusion. This indicated that diffusion through adsorbent mesopores was not responsible for slow desorption from silica gel. Micropore-diffusion modeling of TCE desorption from three silica gels and microporous glass beads indicated that pores less than 2 nm in diameter were responsible for slow desorption. Desorptio...

Superparamagnetic behavior of iron oxides supported on porous silica gels

Spinel iron oxide (Fe3O4-γ-Fe2O3) particles were supported on microbeads of silica gel by the calcination of the silica gel base adsorbing citric acid and Fe3+ ions. The X-ray diffraction patterns and the57Fe Mossbauer spectra measured for the spinel iron oxide indicated that the particle size of the oxide was regulated by the mean pore diameter (4–82 nm) of the silica gel support employed. In the case of α-Fe2O3 particles prepared by using the same silica gel beads, it was revealed by the Mossbauer spectra and the electron micrographs that there were relatively large particles of the oxide on the surface of the beads, in addition to the particles in the silica gel micropores.

The Catalytic Activity of Glass Beads, Silica Gels and Anion-Exchange Resins Modified with Metal-Porphines in the Oxidative Reaction of NADH.

Silica gel and glass beads were modified using the acid chloride of metal-tetrakis(4-carboxyphenyl)porphine (M-TCPP) through a peptide bond, and an anion-exchange resin was modified with M-TCPP by electrostatic interaction and physical adsorption. The carriers modified with Co -TCPP proved to accelerate the following redox reaction : NADH+O2→^^^(carriers modified with Co-TCPP)NAD++H2O2.The formation of hydrogen peroxide was confirmed by means of a colored reaction. The glass beads medified with Co3+-TCPP exhibited the strongest activity among the tested carriers, and were expected to be useful practically as a solid catalyst for the formation of hydrogen peroxide from NADH.

Pore structure and swelling character of porous carbon beads prepared from esterified silica gels

Porous carbon beads have been prepared by a replica method using five silica gels with surface areas ranging from 70 to 765 m2 g−1. The replica method consists of esterification of silica gel with 4-phenyl-1,2-dihyroxybenzene, pyrolysis of the esterified silica gel, dissolution of the silica gel, and drying of the porous carbon from water or, in some cases, from benzene. Porous carbon beads, at maximum, shrank to about 33% of the size of silica gel beads used as a substrate during drying in the preparation. The extent of shrinkage was increased with decreasing surface area of the silica gels. The porous carbons prepared from different silica gels showed a similar pore size distribution, although the distribution became somewhat broader when a silica gel with a small surface area was used. The percentage of expansion of porous carbon beads on adsorbing benzene varied to some extent with the kind of silica gel, and the porous carbon prepared from the silica gel with the surface area of 470 m2 g−1 showed a maximum expansion, 31%. Porous carbon beads dried from benzene showed about 10% higher percentages of expansion on average compared with that from water. Furthermore, in the carbon beads from benzene, a small number of carbon beads showed enormously large expansion, and the expansion was found to be related to the extent of shrinkage during drying in the preparation.