Silica Solid-phase Research Articles

Ketone electrophores and an olefin-release group electrophore-labeled DNA oligomer Detection via electron capture

Sixteen ketone electrophores were synthesized (4′-pentafluorobenzyloxyacetophenone, 1, and fifteen analogs thereof). As intended, each gave a high response by gas chromatography with electron capture detection (GC-ECD) as well as GC with detection by electron capture mass spectrometry (GC-EC-MS). Each spectrum by the latter technique consisted of a single major ion. As a representative compound, 1 was converted to a corresponding olefin, N-hydroxysuccinimide ester, which, in turn, was attached covalently to a DNA oligomer. Detection of the latter species spotted onto a nylon membrane was achieved by the sequence permanganate oxidation (which reformed and thereby released 1), hexane extraction, silica solid phase extraction and GC-EC-MS (giving a peak for 1). These results demonstrate potential for olefin-release group electrophores to function as multiplicity labels in assays involving DNA probes.

Detection and identification of thyreostats in the thyroid gland by gas chromatography-mass spectrometry

Because thyreostatic compounds, also named thyreostats, are banned in Europe (directive 86/469/EEC), methods have to be developed to prevent the illegal use of these substances. The analytical procedure described herein involves the detection and identification at the low ng g −1 level of the main thyreostats known to be used for growth promotion by gas chromatography coupled to mass spectrometry (GC-MS). The assay is based on a liquid/liquid extraction of the thyroid gland, derivatization with pentafluorobenzyl bromide (PFBBr), purification on a silica solid phase extraction column and finally a trimethylsilylation prior to GC-MS. Good thyreostat recoveries were obtained (from 40% to 70%) as well as at acceptable repeatability. The target analytes were detectable below the 1 ng g −1 level on a quadrupole mass spectrometer with negative chemical ionization (NCI) using ammonia as reagent gas and the selected ion monitoring (SIM) acquisition mode. This limit of detection was also reached in the SIM high resolution mode. An improved specificity (more diagnostic ions) was obtained under electronic impact (EI) conditions and positive chemical ionization (PCI) with methane as reagent gas. Identification of thyreostats according to the EU (European Union) criteria (93/256/EEC decision) was made on the basis of two independent GC-MS techniques; the limit of identification was close to 5 ng g −1 for most thyreostats, which represents a real improvement for their control.

Biogenic silica recycling in surficial sediments across the Polar Front of the Southern Ocean (Indian Sector)

The processes controlling preservation and recycling of particulate biogenic silica in superficial sediments must be understood before one uses biogenic silica as a proxy in paleooceanographic studies, and in order to compute oceanic mass balances for silica. In this respect, the Antarctic Ocean is certainly a key region due to its high productivity and export of biogenic silica. In order to quantify sedimentary fluxes and identify crucial processes that allow the preservation of biogenic silica, pore water and solid phase silica profiles were performed on sediment cores from the Southern Ocean (Indian Sector) during the ANTARES 1 cruise. In combination with solubility data reported by Van Cappellen and Qiu (1997a), a process model representing the early diagenesis of silica was developed. In this model, a dependence with depth of the kinetic constant was introduced to allow the preservation of biogenic silica in sediment porewater undersaturated with respect to that phase. Using this steady-state model, it is proposed that a proportionality of the reactivity of the biogenic silica with its settling flux is necessary to explain the observed profiles. It is then shown using this model that the preservation of biogenic silica is not a linear function of the deposited flux. Using a modified version of this model containing an explicit term of reprecipitation, we hypothesize that reprecipitation alone cannot counterbalance dissolution and that its effect is certainly related to a decrease in either surface solubility or kinetics of dissolution.

Determination of the Naturally Derived Insect Control Agent Spinosad in Cottonseed and Processed Commodities by High-Performance Liquid Chromatography with Ultraviolet Detection

A method is described for the determination of the naturally derived insect control agent spinosad in cottonseed and cottonseed processed commodities (meal, hulls, crude oil, refined oil, and soapstock). The method was validated over the concentration range 0.01−0.1 μg/g, with a limit of quantitation of 0.01 μg/g and a limit of detection of 0.003 μg/g. Residues of the active ingredients in spinosad (spinosyns A and D) were extracted from samples with appropriate organic solvents. The extracting solvents were hexane for cottonseed oil, methylene chloride for soapstock, and 60% hexane/40% acetone for cottonseed, meal, or hulls. An aliquot of the extract was purified by liquid−liquid partitioning and silica solid phase extraction. Spinosyns A and D were determined simultaneously in the purified extracts by reversed-phase high-performance liquid chromatography with ultraviolet detection at 250 nm. Confirmation of residue identity was accomplished by reinjecting the same final solution into the chromatograph under different chromatographic conditions. Keywords: Spinosad; spinosyn A; spinosyn D; cottonseed; quantitation; HPLC-UV

Relationships between organo-mineral supply and early diagenesis in the lacustrine environment: A study of surficial sediments from the Lac du Bouchet (Haute Loire, France)

The relationships between organo-mineral composition and early diagenetic processes in surface (< 50 cm) sediments from the Lac du Bouchet (Haute Loire, France) are presented. Parallel pore-water studies reveal downcore increases in dissolved organic carbon, inorganic carbon and CH 4, illustrating the dominant methanogenetic degradation, but also highlighting regions of enhanced degradation due to sulphate reduction (confirmed by solid phase sulphur and pyrite distributions). Three sedimentary facies are observed: IA (0–25 cm) where the majority of compaction and degradation of the organic matter by diagenesis occurs in the absence of any significant change in the type of organic material or sedimentation rate; IB (25–40 cm) characterised by an increased grain size and diatom abundance; II (below 40 cm), whose base dates at 2500 ± 350 BP (i.e. within the Sub-Atlantic) shows high organic carbon contents and large grain size. Autochthonous amorphous organic matter is the dominant petrographical organic component, whereas pedogenetic (allochthonous) amorphous organic matter is slightly enriched in facies II and IA. This is coincident with the disappearance of the spores and pollen and suggests a greater continental runoff from the surrounding basin at these times. Proportions of kaolinite, chlorite and illite content do not vary greatly, indicating that the detrital input has not changed significantly over the last 2500 years. Downcore decreases in the Si Al curve (proxy for biogenic silica) parallel those of total organic carbon suggesting the dissolution of solid phase silica over time. The anthropogenic deforestation and consequent greater nutrient runoff into the oligotrophic lake encouraged an increased production of diatoms around 30 cm. The increased sedimentation rate at the beginning of the Sub-Atlantic (facies II), as a result of greater continental runoff due to installation of present climatic conditions, enhanced the preservation of the organic material by reducing the dia-genetic effects and by increasing the proportion of diagenetically inert and relatively resistant organic matter. These findings underline the critical role that bulk sedimentation rate and the nature of organic matter play in the final determination of sediment composition, both in terms of input and in post-depositional degradation.

The Absorption Spectra of pH Indicator Dyes Doped in Silica Thin Films Prepared by the Method of Liquid Phase Deposition and the Spectroscopic Estimation of Effective Acidity of Internal Hydroxyl Groups of Silica

Abstract The method of liquid phase deposition (LPD) is a wet process forming hard and transparent silica thin films on glass surfaces and has interesting features, such as some organic molecules can be directly doped inside silica phases. The pH indicator dyes methyl yellow and methyl orange were doped in silica thin films by the LPD method and the absorption spectra of the samples were observed. The comparison with the corresponding spectra of the pH indicator dyes in pH-controlled buffer solutions leads to the conclusion that the doped organic dye molecules in the LPD silica solid phase are in an acidic environment equivalent to pH = 3.7. The acidity of the interior of LPD silica is high compared with surface acidity of other silicas such as silica gel. The origin of the high acidity of LPD silica has been attributed to the existence of Si–F bonds inducing an electron-attracting tendency.

The quantitative determination of aspirin and its degradation products in a model solution aerosol

Formulation of pressurized aerosol solutions in propellants for inhalation requires the use of high quantities of surfactants to solubilize the drug. Due to the lipophilic nature of these surfactants, analytical difficulties are created for those wishing to quantify the drug and its degradation products. In order to quantify drug and degradation products by LC it is necessary to separate surfactant and analytes prior to chromatography. To illustrate a typical situation, a method was developed for the analysis of acetylsalicyclic acid (≈2.5 × 10 −3 M) and its major degradation products (salicylic acid, acetylsalicylsalicylic acid and salicylsalicylic acid) solubilized in trichloromonofluoromethane (CFC-11) containing 10 −2 M sorbitan trioleate (Span 85 ®). Surfactant extraction problems were reviewed experimentally. The presentation of all analytes and the surfactant, dissolved in hexane, to silica solid phase extraction columns, followed by elution in a polar solvent, was found to be an efficient way of separating this lipophilic surfactant from the analytes. The final assay employed propellant evaporation, reconstitution of the non-volatiles in hexane, normal phase solid phase extraction (recoveries of 100 ± 10% were observed for all analytes), elution and dilution with mobile phase, and reversed-phase liquid chromatography (Econosphere ® C 8 5 μm, 4.6 × 250 mm). The assay utilized a mobile phase of water, methanol, tetrahydrofuran and 1 M phosphoric acid with ultraviolet detection at 275 nm. Using external standards, linear calibration curves of peak height versus concentration were obtained for all analytes in the expected concentration ranges ( r > 0.991). As it is described, the assay had a relative standard deviation of ≤3.7% for all analytes.

Isolation and Quantification of Ivermectin in Bovine Milk by Matrix Solid Phase Dispersion (MSPD) Extraction and Liquid Chromatographic Determination

Abstract A technique for the extraction and liquid chromatographic determination of ivermectin residues in bovine milk is described. Avermectin was used as an internal standard. Fortified and blank milk samples (5.0 mL) were blended with 2.0 g C18 (octadecylsilyl derivatized silica) in a syringe barrel. After a 2 minute equilibration, the aqueous phase was removed from the column by vacuum aspiration. The ivermectin residues were eluted from the C18/milk matrix with ethyl acetate. After further cleanup by silica solid phase extraction, ivermectin derivatives were formed and then quantified by liquid chromatography with fluorescence detection. The recoveries of fortified ivermectin residues (1.0–8.0 ppb) averaged 97.7%. The injected extracts are free from matrix interferences making it easy to calculate the amount of residue present.

Early diagenesis of silica in sandy North sea sediments: quantification of the solid phase

The suitability of selected alkaline leaching techniques for the quantification of reactive solid phase silica in sandy North Sea sediments was assessed. A single leach in a 2 M Na 2CO 3 solution for 5 h at 85°C resulted in an overestimation of the biogenic silica fraction owing to an increased leachout of silica from clays. Sequential leaching in 0.1 M Na 2CO 3 at 85°C for 5 h yielded two to ten times lower contents. Levels down to 3 μmol g −1 dry sediment were determined. The obtained contents ranged from below 10 μmol g −1 for the erosion dominated stations of the Dogger Bank proper to contents exceeding 20 μmol g −1 for locations north and south of the Dogger Bank. Dissolution of natural sediments in silica-poor seawater allowed for a characterization of the most labile pool of silica. Marked differences between the individual stations in readily soluble silica contents were only observed in the upper layers. The stations at the border of the area had maximal contents exceeding 1 μmol g −1, as compared with below 0.2 μmol g −1 for the others. The consistency between the results of the dissolution experiments, pore-water data and exchange fluxes indicates a control of the pore-water silica concentration by the availability of reactive solid silica in the sediments studied.

Expedient liquid chromatographic analysis of azathioprine in plasma by use of silica solid phase extraction.

We report an expedient analysis of azathioprine (AZN) in plasma by use of a radial compression liquid chromatography and silica solid phase extraction. The separation of the drug and internal standard (antipyrine) was achieved on a C18 cartridge using a mixture of 0.01 M aqueous solution of sodium phosphate (pH = 4.5) and methanol (87:13; vol/vol) as the mobile phase. The assay is highly specific with no interference from any endogenous substance or concomitantly used drug. The peak height ratio of drug to internal standard was linearly (r greater than 0.09976) related to concentration in the range 0.005-2 micrograms/ml, and the within-run and between-day coefficient of variation did not exceed 6.9% at any concentration. This study measured the steady-state concentration of azathioprine in plasma of renal transplants patients. Also, the applicability of this method to study the pharmacokinetics of AZN following a single intravenous administration was examined, using the rabbit as an in vivo model.

Liquid Chromatographic Determination of Paraquat and Diquat in Crops Using a Silica Column with Aqueous Ionic Mobile Phase

A method was developed for the determination of paraquat (PQ) and diquat (DQ) in high moisture food crops. Samples were digested with 6M HCl, and the herbicides were isolated from the digest using pH-controlled silica solid phase extraction. The analytes were then determined by ion-pairing liquid chromatography with a silica analytical column, sodium chloride as the ion-pairing reagent, and acetonitrile as the organic modifier. A diode array UV absorbance detector was used to simultaneously quantify PQ and DQ at their respective maximum absorbance wavelengths, 257 and 310 nm. Average recoveries of PQ and DQ standards from 4 different crops fortified at 0.01-0.50 ppm levels ranged from 79.3 to 104.8%.

Liquid Chromatographic Method for Determination of Citreoviridin in Corn and Rice

Citreoviridin, a neurotoxic mycotoxin, has been found as a natural contaminant in corn left unharvested in the southeastern United States and in rice of several Asian countries, including Japan. A reliable analytical method for the quantitative determination of citreoviridin in corn and rice is described. Corn or rice is extracted with dichloromethane, and the extract is partially purified on silica and amino solid-phase extraction (SPE) columns. The extract is analyzed for citreoviridin by normal-phase liquid chromatography, using a mobile phase of ethyl acetate-hexane (75 + 25) at 1.5 mL/min and a fluorescence detector to measure the yellow fluorescence (388 nm excitation, 480 nm emission). With a 100 microL injection loop, the relationship between concentration and injection volume is linear for 20-60 microL injections. Recoveries of citreoviridin added to yellow corn at 10-50 ng/g were 91.0-96.9%; recoveries from white corn (10-50 ng/g added) were 96.8-102.8%. Recoveries of 5000 ng/g added to white corn were 89.0%, indicating that heavily contaminated samples can be assayed by the method. Minimum detection limits were 10 ng for citreoviridin standard and 2 ng/g for citreoviridin added to corn. White rice fermented with Penicillium citreo-viride (1524 ppm) was mixed with and serially diluted with uncontaminated ground corn to obtain citreoviridin-contaminated corn (ca 25 ppb). When the samples were assayed by the method, a mean level of 24.4 +/- 1.65 ppb (6.5% coefficient of variation) was obtained. Four fermented rice food samples and 3 commercial rice samples were investigated.(ABSTRACT TRUNCATED AT 250 WORDS)