Phenyl Methyl Silicone Research Articles

A Single-Step Extraction for Screening Whole Blood for Basic Drugs by Capillary GC/NPD

Basic drugs were routinely extracted from whole blood under alkaline conditions into n-butyl acetate. An aliquot of the n-butyl acetate was injected into a gas chromatograph equipped with a nitrogen-phosphorous detector and a wide-bore cross-linked 50% phenylmethyl silicone capillary column. Absolute and relative retention times were recorded for more than 100 extracted drug standards. Recovery from whole blood was determined for some of the more frequently encountered drugs. This one-step extraction proved to be reliable for general screening and has been used routinely in forensic and clinical toxicological analyses.

Results of comparative evaluations of various fused silica capillary GC columns for retention of tetrachlorinated dibenzo-p-dioxins and dibenzofurans

Absolute retention times for all twenty-two tetrachlorinated dibenzo-p-dioxin isomers and all thirty-eight tetra-chlorinated dibenzofuran isomers have been measured for several fused silica capillary GC columns coated with a variety of commercially available stationary phases. Data are reported for columns coated with 50% Cyano-propyl, 25% Phenylmethyl silicone (DB-225), 50% Trifluro-propylsilicone (SP-2401), and Polyethyleneglycol (DB-WAX). A two phase loading column for separation of 2,3,7,8-TCDF is presented.

Studies on steroids : CCXXXVIII. Determination of bile acids in liver tissue by gas chromatography-mass spectrometry with negative ion chemical ionization detection

A method for the determination of bile acids in 2–10 mg of human liver tissue by gas chromatography (GC) in combination with negative ion chemical ionization (NICI) mass spectrometry is described. Unconjugated, glycine- and taurine-conjugated bile acids labelled with 18O and 2H were used as internal standards. The preparation of these compounds was attained by the exchange reaction of the carbonyl group with H 2 18O, followed by metal hydride reduction. Bile acids in solubilized liver tissue were extracted with a Sep-Pak C 18 cartridge, separated into the unconjugated, glycine- and taurine-conjugated fractions by ion-exchange chromatography on pipe-ridinohydroxypropyl-Sephadex LH-20 and then derivatized to the pentafluorobenzyl ester—dimethylethylsilyl ethers. Subsequent resolution of each fraction into lithocholate, deoxycholate, chenodeoxycholate, ursodeoxycholate and cholate was attained by GC on a cross-linked 5% phenylmethyl silicone fused-silica capillary column where bile acids were monitored with a characteristic carboxylate anion [M − 181] − in the NICI mode using isobutane as a reagent gas. The newly developed method was applied to the quantitation of bile acids in liver tissue with satisfactory sensitivity and reliability.

GC and GC-MS procedures for simultaneous phenotyping with dextromethorphan and mephenytoin

A genetic deficiency in the metabolism of dextromethorphan and mephenytoin may be revealed by the excretion pattern of dextromethorphan and its metabolite dextrorphan, and mephenytoin, 4-OH-mephenytoin, respectively, after a single dose of the test drugs. Existing methods were modified for determining the compounds in 0.1–0.5 ml urine samples. No prior derivatization of the compounds was necessary before their gaschromatographic or mass-spectrometric analysis by using crosslinked 5% phenylmethyl silicone fused silica columns. Seven healthy volunteers were phenotyped at weekly intervals with either 25 mg dextromethorphan or 100 mg mephenytoin, or both drugs. One subject was a poor metabolizer of mephenytoin, while all subjects were extensive metabolizers of dextromethorphan. Neither a pharmacokinetic nor an analytical interference was observed when the results of the single test were compared with those of the combined test. The results of the mephenytoin test were also tentatively given in form of metabolic ratios. The GC-MS assay was designed for clinical studies so that patients treated with other drugs could be phenotyped.

Equivalent chain-lengths of methyl ester derivatives of fatty acids on gas chromatography A reappraisal

The equivalent chain-lengths of the methyl ester derivatives of synthetic isomeric unsaturated fatty acids in addition to many from natural sources have been determined by gas chromatography (GC) with modern wall-coated open-tubular columns of fused silica coated with Carbowax 20M TM, Silar 5CP TM, CP-Sil 84 TM and a 5% phenyl-methyl silicone. The complete series of cis-octadecenoates (3- to 17-, but not the 2-), the methylene-interrupted cis,cis-octadecadienoates (3,6- to 14,17- but not the 2,5-isomer) and some cis,cis-octadecadienoates with more than one methylene group between the double bonds (5,12-, 6,12-, 7,12-, 8,12-, 6,10- and 6,11-) were used, together with natural fatty acids from pig testis, rich in the ( n−6) family, and from cod liver oil, rich in the ( n−3) family. There were 79 fatty acids in total. The availability of all these data from a single laboratory at one time allows a reassessment of the value of GC equivalent chain-lengths for the identification of unknown fatty acids, and of stationary phases of particular types for fatty acid analysis in general.

A Retention Index Library for Commonly Encountered Drugs and Metabolites Using Tri-n-alkylamines as Reference Compounds, Nitrogen-Phosphorus Detectors, and Dual Capillary Chromatography

The retention index system is a reproducible means for the identification of drugs in toxicology samples analyzed by gas chromatography with flame ionization detectors. Nitrogen-phosphorus (NP) detectors do not respond well to the standard n-alkanes, which lack nitrogen and phosphorus groups and which are used to obtain the Kovats index. A method is presented that creates a retention index library based upon a homologous series of tri-n-alkylamines for a series of 125 drugs and metabolites. Standards were analyzed under temperature programmed conditions by simultaneous dual column chromatography using a 5% phenyl and a 50% phenyl methyl silicone fused-silica capillary column. By increasing the hydrogen and air flows to the NP detectors, the Kovats indices were calculated on the system using the n-alkanes C8 through C32. Tri-n-alkylamine indices calculated under the same conditions were compared to the Kovats indices for 14 drugs on the 5% phenyl column and for 12 drugs on the 50% phenyl column. The correlation was found to be linear. The Kovats indices on the 5% phenyl column were compared to previously reported values and found to be consistent.

Surface Texture Effects in Thin Film Lubrication of Steel by Silicones

The scuff-limited load capacity of both hardened and annealed AISI 52100 steel balls sliding against hardened carbon steel flats were investigated. Silicone oils were used us the lubricants. The test flats were prepared by directional grinding to ∼ 250 nm Ra, then abrading with various grades of abrasive paper. When tested in methylphenyl silicone oil, as-ground flats exhibited the highest load capacity—the smoothest flats, finished on a metallographic polishing wheel with 600-grit abrasive, the lowest. Load capacity flats finished with abrasive paper correlated with the grit size of the abrasive paper: coarser-grit paper produced flats with higher load capacity. As the flats run in, Rq decreased and β* increased such that the surfaces “moved,” in the Rq - β* plane, in a direction approximately perpendicular to lines of constant ψ. Failure occurred when ψ reached a value of ∼ 0.01, regardless of initial surface topography. However, the rougher surfaces with larger initial values of ψ, were able to sustain more wear before failing.

Preparation of glass capillary columns with diphenyl phenylmethyl silicone (OV‐25)

Preparation of glass capillary columns with diphenyl phenylmethyl silicone (OV‐25)

Determination of Ethylene Dibromide in Foods and Grains by High Resolution Capillary Gas Chromatography with Electron Capture Detection

Ethylene dibromide (EDB) levels in food samples were determined by gas chromatography with a high-resolution capillary column and electron capture detector. The capillary column used was 3 mm id X 25 m cross-linked 5% phenylmethyl silicone. Column temperature was set at 40 degrees C by a coolant containing carbon dioxide gas. Optimum temperatures of the injection port and detector were 200 and 350 degrees C, respectively. The detection limit was 0.5 ppb and linear from 1 to 20 pg on the dynamic range. EDB residues in food samples were extracted with n-hexane by steam distillation. A few impurity peaks appeared near EDB on the chromatogram; however, the EDB peak was resolved. Recoveries of EDB from wheat and brown rice ranged from 66.1 to 99.6%. EDB was detected in 3 samples of imported wheat at a range of 0.74-1.70 ppb, and was not detected at all in 37 samples. The EDB remaining in EDB-fortified cookies after baking was examined. The amounts of EDB were reduced to 30 to 50% of the original amounts by kneading the dough, and to below 1.5% by baking.

Volatile compounds in machine cutting-fluid emulsion.

To identify the compounds in machine cutting-fluid emulsion that have an obnoxious odor, we separated volatile components from the emulsion using both steam distillation with a Nickerson–Likens apparatus and vacuum distillation. These components were analyzed by gas chromatography and gas chromatography-mass spectrometry using a fused silica capillary column coated with cross-linked 5% phenylmethyl silicone. 2,6-Dimethyl-3-methoxypyrazine was detected. The main odorous compounds were dimethyl disulfide, dimethyl trisulfide, and 2-butene-1-thiol, the last compound being tentatively identified by its mass spectrum.

Simultaneous determination of codeine and chlorpheniramine in human plasma by capillary column gas chromatography

A specific and highly sensitive capillary column gas chromatographic method was developed for the simultaneous determination of codeine and chlorpheniramine in human plasma. The method involves a solvent extraction and analysis by capillary column gas chromatography on a cross-linked 50% phenylmethyl silicone fused-silica capillary column with flame thermionic detection. A 10% solution of n-butanol in toluene was used as extraction medium and pyrilamine was used as internal standard. Reproducibility, linearity of calibration curves and specificity were all satisfactory with both drugs. The plasma concentration of codeine and chlorpheniramine could be measured at levels down to 0.9 ng/ml as codeine phosphate and 0.4 ng/ml as chlorpheniramine maleate, respectively. The method was applied to plasma samples from normal volunteers, and was confirmed to be adequate for biopharmaceutical and pharmacokinetic studies.

Selectivity and selectivity tuning in capillary gas chromatography

AbstractThe selection of stationary phases in capillary gas chromatography is discussed. Methyl silicone, phenyl methyl silicone, trifluoropropylmethyl silicone, biscyanopropyl silicone, and high molecular weight (HMW) polyethylene glycol are considered to be the basic phases. Selectivities and polarities between these phases are obtained by selectivity tuning. Selectivity tuning can be performed in three different ways, namely by synthesizing a tuned stationary phase, by mixing the basic phases, or by coupling capillary columns of different selectivities. In coupling capillary columns the variables are column length, β‐value, temperature, and/or pressure.

Quantum chemical parameters in correlation analysis of gas—liquid chromatographic retention indices of amines

For a structurally diverse set of primary, secondary and tertiary heterocyclic amines, correlations were found between the Kováts retention indices obtained on the methyl phenyl silicone phase OV-101 and quantum chemically calculated parameters. The total energy calculated by CNDO/2 molecular orbital method was chosen as a measure of a solute's ability to participate in dispersive interactions with the stationary phase. As a measure of the solute's ability to undergo polar interactions with the stationary phase, a parameter was proposed which reflects the highest local intermolecular dipole moment. It is defined as the largest difference in electron charges between two atoms. A two-parameter regression equation was derived which describes satisfactorily the retention of structurally different polar solutes on a relatively non-polar stationary phase. Some evidence is also provided that charge-transfer complexes are formed during the separations process.

The technical examination and conservation of the portal of St Aquilino’s chapel in the basilica of St Lorenzo, milan

The chapel of St Aquilino, part of the basilical complex of St Lorenzo in Milan, has a sculptedportal of the Roman age. Following a request by Soprintendenza I Archeologica della Lombardia, the portal was subjected to an historical, technical and conservation study. Different techniques were used, including light and electron microscopy, X-ray diffraction and fluorescence, and porosimetry. The analyses showed that the portal is sculpted in a thin slab of Carrara marble and is covered in many places by a crust of gypsum. The different kinds of mortar, used for various restorations, indicate that the portal is the same age as the mosaics of the chapel (fourth-fifth century AD). The portal was cleaned with distilled water and Attapulgite packs, and thenconsolidated with methylphenyl silicone resin. The fragments of the epistyle were sealed, and fixed with Teflon pins.

Gas chromatographie behaviour of some metal acetylacetonates

The gas Chromatographie behaviour of metal Cr(III), Al(III) and Co(III) chelates on columns containing OV-17 and OV-25 methyl phenyl silicone oil as the liquid stationary phase at different temperatures and different flow ratios was investigated. The optimum separation conditions for investigated acetylacetonates mixture have been evaluated. The temperature of 200–250° C range and 60–90 cm3/min flow ratio were found to be the best.

Capillary gas chromatographic separation of urinary organic acids. Retention indices of 101 urinary acids on a 5% phenylmethyl silicone capillary column.

Gas chromatographic retention indices (methylene units) are reported for 101 urinary organic acids as their trimethylsilyl and oximated trimethylsilyl derivatives on a 5% phenylmethyl silicone fused silica capillary column. Using anion exchange chromatography, organic acids were extracted from urines of five healthy individuals, seven patients with neuroblastoma, and nine patients with inherited organic acidurias. Separation of the various acids was achieved by capillary gas chromatography and identification was done by mass spectrometry using a computerized library search program. All identifications were confirmed by visual comparison with reference mass spectra. Standard deviations of the retention indices for all acids were less than 0.035 methylene units and for 46 acids less than 0.01 methylene units. Three chromatograms of urine from individuals with neuroblastoma, phenylketonuria, and propionic acidemia and one from a healthy individual are shown.

Conduction Mechanisms and Time Dependence of Sensing Characteristics on SiO<SUB>2</SUB> Humidity-Sensitive Films

The electrical conduction mechanisms of three types, of films have been investigated in relation to humidity-electrical resistance characteristics and their variations with time. Type I film consisted of heat-treated methylphenyl silicone and SiO2. Type II film consisted of a heat-treated mixture of silicone, SiO2, and Na2CO3. Type III film was a heat-treated mixture of silicone, SiO2, and graphite. The dominant charge carriers for the surface electrical conduction were thought to be protons in type I, hydrated sodium ions in type II, and protons and electrons in type III, respectively. The electrical resistance of type I increases and that of type II decreased with time of exposure to the laboratory air. The time dependence of the humidity-resistance characteristic of type III was less than that of other two types. However, the humidity-sensitivity of type III was not very good.

Advances in fused-silica column technology for the analysis of underivatized drugs

The chemical durability of a cross-linked 5 % phenyl methylsilicone stationary phase is investigated for the analysis of underivatized drugs. Column performance is tested with respect to quantitative reproducibility, solvent extractability, selectivity for various drug families, and capacity for the polar solute. Data are presented showing the effects of a polar solvent and a serum extract on column lifetime with splitless and cool on-column injection. Examples of a human drug screen and the forensic analysis of street heroin are provided.

Crosslinked methylphenylsilicones as stationary phases for capillary gas chromatography

Methyl(phenyl)silicones offer useful selectivities when used as stationary phases in gas chromatography (GC). Such phases have, however, hitherto been of restricted importance in capillary GC due to the lack of phases having a viscosity high enough to ensure stationary phase film stability. Further, to utilize fully the possibilities of a methyl(phenyl)silicone capillary column, it must also possess high efficiency and a high degree of deactivation.

Augmentation of Direct-Contact Heat Transfer to Drops with an Intermittent Electric Field

The characteristics of the augmentation technique previously proposed by the authors has been studied experimentally with water drops 3.9 to 5.9 mm in diameter rising in methylphenyl silicone oil. Each drop is subjected to an intermittent electric field applied periodically perpendicular to its trajectory, and the drop responds by periodic elongation in the direction of the field. The dependence of heat transfer coefficient on the strength, frequency and duty ratio of the field is presented and discussed.