Methyl Silicone Research Articles

Essential oils of camphor tree (cinnamomum camphora nees & eberm) cultivated in Southern Brazil

The essential oils of two varieties of Camphor tree (Cinnamomum camphora Nees & Eberm, Lauraceae), known as Hon-Sho and Ho-Sho cultivated in experimental stands in Southern Brazil were studied. The essential oils were obtained from the leaves and twigs of young plants by hydrodistillation. The identification of the components was performed using GC, GC/MS and retention indexes on methyl silicone and carbowax phases. The main components identified were linalool in the Ho-Sho and camphor in the Hon-Sho.

Intermediate wettability by chemical treatment

To study the effect of wettability on recovery, we used a chemical additive that changes the surface properties of natural rock samples while keeping interfacial tension and viscosity constant. The wettability change is weaker than for other chemical treatments (e.g., silane) and is therefore closer to reservoir cases. The chemical additive is a potassium methyl siliconate that is soluble in water. A polymerization of the adsorbed layer on the pore surface is obtained when the pH is lowered near neutral. Outcrop sandstone samples were treated either with or without the presence of oil (at Swirr) using carbon dioxide as a neutralizer. Efficiency of the treatment is determined mainly by comparing centrifuge (negative) imbibition capillary pressure curve on treated and untreated samples. Micropore membrane technique was also applied to measure the positive imbibition capillary pressure curve. The main results are (1) the final oil saturation (Sor) is reduced from 0.4 to 0.3 and 0.1 depending on how the treatment was performed; (2) there are only minor modifications on the primary drainage capillary pressure curve; and (3) water relative permeability at Sor measured after centrifuge forced imbibition is not modified by the treatment.

Adsorption and displacement of beta-2-microglobulin at solid/liquid interfaces

Adsorption of beta-2-microglobulin from aqueous solution onto unmodified and methylated silicon wafers and subsequent displacement of the small globular protein by fibrinogen were studied by spectroscopic ellipsometry, immunosorbent assays and atomic force microscopy. The results provide evidence that hydrophobicity of the substrate increases the maximum adsorbed amount of beta-2-microglobulin and the resistance of the adsorbed protein to displacement from the interface by competing species, respectively. Further, the dynamics of beta-2-microglobulin adsorption was found to induce significant differences in the degree of displacement achieved at given conditions. The observed variations in displacement behavior of adsorbed beta-2-microglobulin were interpreted based on information on the layer structure gained by atomic force microscopy. More compact and relatively smooth protein layers were formed on the hydrophobic surface corresponding to lower displacement by fibrinogen.

Determination of 4-hydroxyifosfamide concomitantly with ifosfamide and its dechloroethylated metabolites using gas chromatography and a nitrogen phosphorus-selective detector

A sensitive gas chromatographic (GC)/nitrogen phosphorus detection (NPD) system was developed for the determination of the antitumor drug ifosfamide (Ifos) and its 2-dechloroethylifosfamide (2-Difos), 3-dechloroethylifosfamide (3-Difos) and 4-hydroxyifosfamide (4-OHIfos) metabolites in human blood. 4-OHIfos was analyzed after coupling with a trapping agent and was used as an indicator of isophosphoramide mustard (IPM). Ifos and its metabolites 2-DIfos, 3-DIfos, 4-OHIfos and the internal standard (trofosfamide) were extracted into chloroform and then resolved by gas chromatography using a Hewlett Packard HP5 capillary column cross-linked with 5% phenyl methyl silicone (30 m; 530 μm I.D.; 2.65 μm film thickness). Precision and accuracy of the assay were determined over a three-day period and a concentration range of 3.25–50 μg/ml for Ifos, 0.8–14 μg/ml for 2D-Ifos, 0.6–10 μg/ml for 3D-Ifos and 0.08–1.40 μg/ml for 4-OHIfos. The limit of quantitation was set at 3.25, 0.80, 0.62 and 0.08 μg/ml, respectively, for Ifos, 2-DIfos, 3-DIfos and 4-OHIfos.The intra- and inter-day coefficients of variation and accuracies were less than 20%, except for a low concentration 4-OHIfos. This assay was then used to provide pharmacokinetic data on antitumor and toxicologic effects following intravenous infusion of Ifos.

Determination of the wax ester content in olive oils. Improvement in the method proposed by EEC regulation 183/93.

A simpler and faster procedure than the official one described in document IV of European Economic Community Regulation 183/93 is proposed. The wax ester fraction is isolated from triglycerides using a commercially available silica gel column and carbon tetrachloride as eluent. The recovered wax ester fraction, with the addition of a suitable internal standard solution, is analyzed by gas chromatography. A column with a 65% phenyl methyl silicone stationary phase allows a satisfying separation of wax ester fraction in comparison with both a steryl ester and a light fraction eluted before the internal standard. Furthermore, also the single components of the wax ester fraction are suitably separated.

Routine analysis of plasma busulfan by gas chromatography–mass fragmentography

Busulfan (BU) is a widely used alkylating agent for antineoplastic therapy and marrow ablation in preparation for bone marrow transplantation (BMT). High-dose BU often leads to successful preparation and low relapse but is associated with veno-occlusive disease of liver. We established a protocol to determine postdosage plasma BU concentrations by gas chromatography-mass fragmentography in an attempt to relate clinical outcome to plasma BU concentrations. We used nonisotopic pusulfan as the internal standard. After extraction into ethyl acetate, BU and pusulfan were iodinated into 1, 4-diiodobutane and 1,5-diiodopentane, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis was carried out on an Hewlett-Packard (HP) 5890II gas chromatograph with a 30-m 100% methyl silicon narrow bore, fused-silica capillary column interfaced with an HP 5970A mass spectrometer. Helium was the carrier gas. The sample molecules were identified by total ion monitoring and quantified by selective ion monitoring of m/z 183 and 197. The calibration curve was linear to 4 mg/L. The limit of quantification was 0.04 mg/L, and the analytical recovery was approximately 97%. The within-day and between-day imprecision (CV) was <6% and 9%, respectively. In a preliminary study of 12 children, the BU areas under the BU-time curve were 616-949 micromol. min/L after the first dose and 793-1143 micromol. min/L after the fifth dose. We conclude that the GC-MS procedure is suitable for routine analysis of plasma BU.

Immobilized chicken antibodies improve the detection of serum antigens with surface plasmon resonance (SPR)

Surface plasmon resonance (SPR) and other refractive index and mass sensitive methods are, due to complement activation by mouse monoclonal antibodies and with concomitant high background signal, only rarely used for the detection of antibody–antigen interactions in the blood serum milieu. In the present study chicken IgY and mouse IgG were immobilized to a sensor chip CM5 dextran matrix and compared for their background signal and detection of serum antigen. Ellipsometry with antibodies adsorbed to methylated silicon surfaces was used as a complementary detection method. As expected, fundamental differences in binding properties between the two kinds of antibodies were observed. Mouse antibodies bound large quantities of human serum. Human C1q was detected on mouse IgG and the complement system was activated, as seen from the rapid C3 and properdin depositions. Chicken antibodies bound low quantities of human serum and no human C1q. Moreover, C3 and properdin deposited only after prolonged serum incubations. Addition of EDTA to serum reduced the background signal modestly for both IgG and IgY. Serum samples with different concentrations of human C3 were injected over surfaces with immobilized chicken anti-C3, and the response was measured by SPR. Small concentration differences (<1.25 μg/ml) in a physiologically relevant range (1–40 μg/ml after 100 times dilution) could then be detected reproducibly. The SPR signal was totally obscured when a mouse monoclonal anti-C3 antibody was used for the detection.

Determination of Diethanolamine and N-Nitrosodiethanolamine in Fatty Acid Diethanolamides

Diethanolamine (DEA) is a precursor of N-nitrosodiethanolamine (NDELA), an animal carcinogen. A gas chromatographic (GC) method was developed for determining DEA in fatty acid diethanolamides that are commonly used in cosmetic products. Methanolic solutions of the amides were analyzed by GC with flame ionization detection on either a wide-bore methyl silicone (Rtx-1) or 95% dimethyl--5% diphenyl polysiloxane (SPB-5) capillary column. Recovery of DEA from fatty acid dialkanolamides at fortification levels of 0.50, 1.00, and 5.00% ranged from 94 to 100%. In a survey of commercial fatty acid diethanolamides, DEA was found at levels ranging from 1.1 to 14.0%, and most were in good agreement with manufacturer's DEA specifications. Fatty acid diethanolamides also were anlayzed for NDELA by liquid chromatography interfaced to a thermal energy analyzer. Recovery of NDELA from fatty acid diethanolamides at fortification levels of 50, 100, and 200 ppb averaged 95%. No NDELA was found in any of the fatty acid diethanolamide samples analyzed.

The Relationship of Kovaacgrts Retention Indices and Equivalent Chain Lengths of Fatty Acid Methyl Esters on a Methyl Silicone Capillary Column

The Kovats retention indices of normal paraffins, fatty acid methyl esters (FAMEs), and fatty alcohols separated on a 15 m × 0.25-mm i.d. OV-101 capillary column are calculated directly from their retention data. Also, the described equations are used to convert the equivalent chain length value of FAMEs to retention indices or vice versa. All the calculated retention indices are in good agreement with those reported in the literature.

Chemistry of the direct synthesis of methylchlorosilanes. UHV study of the chemisorbed fragments methyl and chlorine on copper silicide and their desorption pathways

The Direct Synthesis of methylchlorosilanes from methyl chloride and silicon, catalyzed by copper and minor promoter elements was reviewed with respect to use of ultra-high vacuum (UHV) surface reaction techniques to uncover the mechanism of the reaction. In particular, recent results were presented for sequentially adsorbing methyl radicals and chlorine on polycrystalline Cu 3Si alloy under ultra-high vacuum conditions. Methyl monolayers in the absence of chlorine produced primarily trimethylsilane, and chlorine monolayers in the absence of methyl produced SiCl 4. However, mixed monolayers of methyl groups with chlorine atoms abandoned these separate pathways and instead reacted at similar temperatures on the surface to produce methylchlorosilanes with selectivities to 85% Me 2SiCl 2 with Zn, Sn, and Al as promoters.

Monitoring of S- and R-tocainide in human plasma after heptafluorobutyrylation, separation on Chirasil-Val and electron-capture detection.

The conditions for the heptafluorobutyrylation of tocainide have been studied. An almost instantaneous reaction was obtained with 0.01% of heptafluorobutyric anhydride in toluene at 40 degrees C. Higher anhydride concentration caused degradation of the initially formed derivative, mainly by the loss of water, as shown by mass spectral analysis. Tocainide was isolated from plasma by extraction into dichloromethane at alkaline pH. Gas chromatographic separation was performed with a fused-silica capillary column coated with a methyl silicone gum. The enantiomers were separated on a glass capillary column coated with Chirasil-Val. Upon analysing 0.1 ml of plasma eight times the precision was 4.7% at the 10 mumol/1 level for the S-form of tocainide.

Application of solid-phase extraction in the method development for determination of SEPA, an acronym for soft enhancement of percutaneous absorption, in human, rat, and rabbit serum using GC–FID method

A new nonaqueous topical minoxidil formulation containing SEPA (2- n-nonyl-1,3-dioxolane) for enhancement of percutaneous absorption was under evaluation. SEPA does not have chromophore for either ultraviolet or fluorescence detection using liquid chromatography and has no functional groups for derivatization. Therefore, a direct gas-chromatographic method with flame-ionization detection (GC–FID) was developed. Owing to the limited detection response of the FID detection, it needs a selective and concentrated extract for GC–FID analysis to improve the assay sensitivity to meet the requirement for pharmacokinetic evaluation after topical application. In addition, SEPA is a very volatile compound. Any extraction procedures involving evaporation will result in a poor recovery. The application of solid-phase extraction (SPE) makes it possible to achieve a selective and a 10-fold concentrated extract with an absolute extraction recovery of approximately 90%, which greatly improved the assay sensitivity. This method involved the extraction of SEPA and the internal standard (2- n-heptyl-1,3-dioxolane) from serum (0.1–1 ml) with 100 μl of hexane-chloroform (1:1, v:v) using a 50 mg 1.0 ml −1 phenyl SPE column (Varian, Harbor City, CA, USA), followed by direct GC–FID analysis on a fused-silica column chemically bonded with cross-linked methyl silicone gum phase (Hewlett Packard Ultra-1, 12 m×0.2 mm×0.33 μm, Avondale, PA, USA). The assay demonstrated a lower limit of quantitation of 2.5 ng ml −1 and a linear range of 2.5 to 250 ng ml −1 with intra- and inter-assay precision and accuracy of ≤10%.

Retention indices of alkenes and the corresponding epoxides on a capillary column coated with cyanopropyl methyl silicone phase

Retention indices or five 1-alkenes, seven branched alkenes and five cycloalkenes and the corresponding epoxides were determined at two temperatures on a fused-silica capillary column coated with cyanopropyl methyl siloxane to interpret their chromatographic behaviour. The standard deviation was 0.2 index units.

Ellipsometery and radio-labelling studies on the adsorption of human serum albumin (HSA) and anti-HSA to hydrophobic silicon

Ellipsometry and radio-labelling techniques were employed to study the deposition of human serum albumin (HSA) followed by excess of mono- or polyclonal anti-HSA to methylated silicon. Adsorbed HSA, and [HSA-monoclonal anti-HSA] layers were rapidly removed by 0.1-0.5% SDS, but [HSA-polyclonal anti-HSA] layers were not. The results suggest that antigens and polyclonal antibodies crosslink on surfaces, thereby stabilizing the protein films. Upon five repetitive and alternating exposures to excess of HSA and polyclonal anti-HSA, it was observed that the ellipsometric thickness did not increase during HSA incubations but did so during the polyclonal antibody incubations. When [HSA-polyclonal anti-HSA] multilayers were exposed to 125I-HSA, a low increased deposition with time of 125I-HSA was observed. HSA was, however, not able to remove 125I-HSA from [ 125I-HSA-polyclonal anti-HSA] films. The protein deposition and binding characteristics are presently not well understood but may be explained by a low HSA deposition to surface-bound polyclonal antibodies, the multiplicity of antibody binding sites on each HSA molecule, and a partial disruption of the antigen-antibody complex structure upon incubation in excess of HSA.

Quantitation of cocaine and cocaethylene in small volumes of rat whole blood using gas chromatography-mass spectrometry

A simple solid phase extraction (SPE) technique combined with gas chromatography-mass spectrometry (GC/MS) operated in selected ion monitoring (SIM) mode is described for quantitation of cocaine and cocaethylene in small samples (250 μl) of rat whole blood. Use of ( N-[ 2H 3C])-cocaine and (N- [ 2H 3C])-cocaethylene internal standards resulted in high sensitivity and selectivity for this analytical method. Analysis was performed using a Hewlett-Packard 5890 GC equipped with a 7673A Automatic Liquid Sampler linked to a Hewlett-Packard 5972 Mass Selective Detector. Separation of analytes was accomplished on a cross-linked methyl silicone gum capillary column (Ultra 1: 12m × 0.2mm (i.d.) × 0.33 μm). Linearity was established over a wide range of concentrations (5.0–2000.0 ng ml −1) with good precision. Limits of detection (LOD) were 1.0 and 2.0 ng ml −1 for cocaine and cocaethylene, respectively. This analytical method was designed for use in pharmacokinetic experiments studying the formation of cocaethylene following ethanol pretreatment in rats administered cocaine.

Temporal studies on the deposition of complement on human colostrum IgA and serum IgG immobilized on methylated silicon.

The temporal deposition of selected complement proteins from human serum onto immobilized human colostrum immunoglobulin (Ig)A and human IgG on hydrophobic silicon was studied by ellipsometry-antibody techniques after incubations at 37 degrees C for up to 1 h. In parallel experiments the serum soluble iC3b, C4d, and Bb were detected by enzyme-linked immunosorbent assay techniques. The IgA-coated surfaces showed activation via the alternative pathway, and displayed a lag phase in the deposition of increased amounts of serum proteins, and anti-C3c and antiproperdin. Anti-IgG, -C1q, -C4, -factor H and -factor B were not deposited at any time to IgA surfaces. Upon coating of the surface with IgG, the classical pathway was rapidly activated and bound, then anti-C3c, antiproperdin, and after short serum incubation times, also anti-C1q and anti-IgG. When factor B-depleted or heat-treated sera were used, the observation was that properdin deposited onto IgG-coated surfaces from both. Ellipsometry and antibody techniques offer a convenient and rapid way to indicate the activation of the complement system on solid surfaces and facilitates a time-resolved determination of the activation pathway(s).

Qualitative and Quantitative Analysis of Flavor Additives on Tobacco Products Using SPME−GC−Mass Spectroscopy

Headspace solid-phase microextraction−gas chromatography−mass spectroscopy (HS-SPME−GC−MS) has been used for both qualitative and quantitative analysis of flavor additives to tobacco. Sampling conditions for the 100 μm methyl silicone fiber, 65 μm polyacrylate fiber, 65 μm methyl silicone/divinylbenzene fiber, and 65 μm Carbowax/divinylbenzene fiber were investigated. Menthol, anethole, benzaldehyde, and tetramethylpyrazine were quantitated on spiked Kentucky Reference 1R1 tobacco. Major components in mandarin orange oil, nutmeg oil, and sweet fennel oil exhibited linear relationships with concentration of the essential oil. Limits of detection for 31 typical tobacco flavors have been determined. Keywords: Flavor additives; tobacco; solid-phase microextraction; gas chromatography; mass spectroscopy; headspace.

New method for estimating vapor pressure by the use of gas chromatography

We have developed a new, simple, quick, precise and inexpensive method to estimate vapor pressure by the use of gas chromatography. This new method differs significantly from previous gas chromatography methods because it uses a temperature gradient rather than a series of isocratic experiments extrapolated back to room temperature using the Clausius-Clapeyron equation. In addition, it uses a typical methyl silicone capillary column rather than a short (1 m) non-polar capillary. To improve reproducibility of results between different instruments, a cocktail containing two standards with well-established vapor pressures is injected along with the sample compound(s). The vapor pressure at 25°C of the compound(s) in the liquid state is determined by simply finding the retention times of the compound(s) and those of the two standards. Corrections can be made for crystalline compounds. This method can be used for the measurement of the vapor pressures of organic compounds ranging from 10 2 to 10 −7 Pa at 25°C (1 mmHg to 10 −9 mmHg).

Effect of Chilling on Cyanide-resistant Respiration and Carbohydrate Status in Chilling-sensitive and -resistant Species

The effect of chilling stress on induction of the cyanide-resistant pathway was investigated using roots of 3-day-old cucumber (Cucumis sativus L.) and 5-day-old pea (Pisum sativum L.) grown at 26°C, and then chilled at 2°C for 48 or 96 hours for cucumber, and 72 or 192 hours for pea. A 24-hour post-chilling treatment at 26°C was imposed on different sets of chilled roots from both crops. Carbohydrate status was determined by gas chromatography with an autosampler using a 12.5-m cross-linked methyl silicone capillary column (0.1 mm). Exposing seedlings to 2°C, as well as to a postchilling treatment, induced differential responses in the activity of the cyanide-resistant pathway. Cucumber seedling roots exhibited an accumulation of fructose, glucose and sucrose during chilling, with a rapid decline observed during the post-chilling treatment at 26°C. Pea seedling roots maintained a constant level of carbohydrates throughout the chilling period, and exhibited a slight decrease by the end of 192 hours at 2°C. There was an increase in carbohydrate levels during the post-chilling treatment. The involvement of the cyanide resistant pathway and carbohydrate changes will be discussed.

Complement activation by IgG immobilized on methylated silicon.

Activation of the complement system by immobilized IgG on methylated silicon was studied by ellipsometry/antibody-, ELISA-, and RIA techniques after exposure to human serum at 37 degrees C for up to 1 h. The IgG-covered surfaces rapidly activated the complement system and the combined results suggest an initial classical pathway activation. Complement factor 1q (C1q) and IgG were antibody-detectable on the surfaces for serum incubations up to 5 min but not thereafter. Anti-C3c and anti-properdin bound to the surfaces at all serum incubation times. Experiments with 125I-IgG preadsorbed to surfaces, or added to normal-, EGTA-, and EDTA-sera, showed that IgG was not displaced from the protein film by serum.