Atmosphere international standard

Finally, other methods are used to obtain simulated distillation by gas phase chromatography for atmospheric or vacuum residues. For these cases, some of the sample components can not elute and an internal standard is added to the sample in order to obtain this quantity with precision. 

TABLE 2-236 Thermodynamic Properties of the International Standard Atmosphere ... 

The MDA experiments were performed in a continuous down-flow fixed bed reactor at 700°C, atmospheric pressure, and a space velocity of 1500 em3/(gcat h). Catalysts were pretreated in He flow at 700°C for 30 min before feeding a CH4 N2 mixture in a 9 1 voEvol ratio (N2 used as internal standard). Unreacted methane, the reference N2, and the reaction products were analyzed on line in a gas chromatograph (HP-GC6890) as detailed in [6]. Product selectivities are given on a carbon basis. The use of N2 as internal standard allows to obtain the amount of carbonaceous residues as the amount of carbon required to close the mass carbon balances to 100%. 

General Methods. Methanol used in kinetic runs was distilled from sodium methoxide or calcium hydride in a nitrogen atmosphere before use. Freshly distilled cyclohexanol was added to the methanol in the ratio 6.0 ml cyclohexanol/200 ml MeOH and was used as an internal standard for gas chromatographic (GC) analysis. Benzaldehyde was distilled under vacuum and stored under nitrogen at 5°. Other aldehydes (purchased from Aldrich) were also distilled before use. The corresponding alcohols (purchased from Aldrich) were distilled and used to prepare GC standards. All metal carbonyl cluster complexes were purchased from Strem Chemical Company and used as received. Tetrahydrofuran (THF) was distilled from sodium benzophenone under nitrogen before use. 

Liang, H.R. Foltz, R.L. Meng, M. Bennett, P. Ionization enhancement in atmospheric pressure chemical ionization and suppression in electrospray ionization between target drugs and stable-isotope-labeled internal standards in quantitative liquid chromatography/tandem mass spectrometry. Rapid Commun. Mass Spectrom. 2003, 17, 2815—2821. 

Method A solution of p-methoxyphenyltellurium trichloride (0.34 g, 1.0 mmol) in benzene (200 mL) is irradiated with a high-pressure mercury lamp in the presence of atmospheric oxygen for 1 h (formation of a black precipitate). The mixture is filtered and the filtrate is washed with brine and then dried (MgS04). GLC analysis shows the presence of p-chloromethoxybenzene [0.14 g (70%)] (and minor amounts of o,p-dichloro-methoxy-benzene and p-methoxybiphenyl) using p-chlorotoluene, 2,4-dichlorotoluene and p-methylbiphenyl as the internal standard, respectively. 

All NMR spectra were recorded on a Varian A-60 spectrometer at room temperature by Nuclear Magnetic Resonance Specialties, Inc., New Kensington, Pa. Benzene soluble fractions were recorded in deuterated chloroform solution (CDCls) while dimethyl sulfoxide-dc (DMSO-dr.) was the solvent employed for other fractions. (Deuterated chloroform with enrichment of 99.8% was purchased from Bio-Rad Laboratories and dimethyl sulfoxide-dr, with enrichment of 99.6% from Merck, Sharp, and Dohme of Canada.) The internal standard used with the CDCla solutions was tetramethvlsilane and hexamethyl-disiloxane (chemical shift 7 c.p.s.) with DMSO-d . Prior to preparation for NMR recording, the samples were thoroughly dried in a vacuum at 110°C. The NMR tubes were sealed to minimize the absorption of atmospheric moisture. The chemical shifts given in c.p.s. are referred to tetramethylsilane. 

Catalyst batches were activated under two different activation conditions H2/CO (with 3% Ar) = 2.6 3.87 xmol/s (FT synthesis reaction mixture with H2/CO = 0.7) for 2 h at (1) 523 K and (2) 543 K. These conditions are based on temperatures and gases used by PETC to activate these catalysts for testing prior to a large scale pilot plant run. After activation, reactions were carried out over the catalyst samples in the same reactor tube at 523 K with H2/CO = 0.7 and a total gas flow rate of 6.47 pmol/s (with Ar as internal standard) at a pressure of 83.8 kPa (normal atmospheric pressure in Albuquerque). Two sets of samples were made, one for each of the two activation conditions. Each set consisted of three samples after activation, activation followed by FT reaction for 10 h, and activation followed by FT reaction for 45 h. In the case of the activation at 523 K, the first 2 h of the run were considered the activation step. Therefore, the activation in this case was at 523 K. For activation at 543 K, the catalyst bed was cooled to 523 K in the syngas mixture of activation. 

Stenhoff et al. [117] determined enantiomers of omeprazole in blood plasma by normal-phase liquid chromatography and detection by atmospheric-pressure ionization tandem mass spectrometry. The enantioselec-tive assay of omeprazole is using normal-phase liquid chromatography on a Chiralpak AD column and detection by mass spectrometry. Omeprazole is extracted by a mixture of dichloromethane and hexane and, after evaporation, redissolution and injection, separated into its enantiomers on the chiral stationary phase. Detection is made by a triple quadrupole mass spectrometer, using deuterated analogs and internal standards. The method enables determination in plasma down to 10 nmol/1 and shows excellent consistency suited for pharmacokinetic studies in man. 

Martens-Lobenhoffer et al. [119] used chiral HPLC-atmospheric pressure photoionization tandem mass-spectrometric method for the enantio-selective quantification of omeprazole and its main metabolites in human serum. The method features solid-phase separation, normal phase chiral HPLC separation, and atmospheric pressure photoionization tandem mass spectrometry. The internal standards serve stable isotope labeled omeprazole and 5-hydroxy omeprazole. The HPLC part consists of Agilent 1100 system comprising a binary pump, an autosampler, a thermo-stated column component, and a diode array UV-VIS detector. The enantioselective chromatographic separation took place on a ReproSil Chiral-CA 5 ym 25 cm x 2 mm column, protected by a security guard system, equipped with a 4 mm x 2-mm silica filter insert. The analytes were detected by a Thermo Scientific TSQ Discovery Max triple quadrupole mass spectrometer, equipped with an APPI ion source with a... 

Song and Naidong [129] analyzed omeprazole and 5-hydroxyomepra-zole in human plasma using hydrophilic interaction chromatography with tandem mass spectrometry. Omeprazole and its metabolite 5-hydroxy omeprazole and the internal standard desoxyomeprazole were extracted from 0.05 ml of human plasma using 0.5 ml of ethyl acetate in a 96-well plate. A portion (0.1 ml) of the ethyl acetate extract was diluted with 0.4 ml of acetonitrile and 10 /il was injected onto a Betasil silica column (5 cm x 3 mm, 5 /rm) and detected by atmospheric pressure ionization 3000 and 4000 with positive electrospray ionization. Mobile phase with linear gradient elution consists of acetonitrile, water, and formic acid (from 95 5 0.1 to 73.5 26.5 0.1 in 2 min). The flow-rate was 1.5 ml/min with total rim time of 2.75 min. The method was validated for a low limit of quantitation at 2.5 ng/ml for both analytes. The method was also validated for specificity, reproducibility, stability, and recovery. 

Hultman et al. [130] developed a LC/MS/MS method for the quantitative determination of esomeprazole and its two main metabolites 5-hydro-xyesomeprazole and omeprazole sulfone in 25 /il human, rat, or dog plasma. The analytes and their internal standards were extracted from plasma into methyl ferf-butyl ether-dichloromethane (3 2). After evaporation and reconstitution of the organic extract, the analytes were separated on a reversed-phase liquid chromatography column and measured by atmospheric-pressure positive ionization mass spectrometry. 

LLE liquid-liquid extraction, SPE solid phase extraction, LPME liquid-phase microextraction, ESI electrospray ionization, APCI atmospheric pressure chemical ionization, SSI sonic spray ionization, Q quadrupole, QqQ triple quadrupole, TOF time-of-flight, IT ion trap, IS internal standard, CV coefficient of variation, MRE mean relative error, LOD limit of detection, LLOQ lower limit of quantification... 

A solution of 7.5 g 2-nitrobenzyl alcohol, 2% TEMPO, 2% Mn(N03)2, 2% Co(N03)2, in 39 mL CH3COOH was stirred at 40 °C for 6h under 02 at atmospheric pressure. GC analysis (p-chlorobenzaldehyde as internal standard) revealed 2-nitrobenzaldehyde in 99% yield. On evaporation of CH3COOH, the residue was dissolved in CH2C12. Flash column chromatography on silica gel yielded 6.9 g of pure 2-nitrobenzaldehyde (m.p. 44°C 93 % yield). 

A solution of 3 mmol 3-cyanobenzyl alcohol, 0.3 mmol N-hydroxyphthalimide, 0.015 mmol Co(OAc)2, and 0.15 mmol m-chlorobenzoic acid in 15 mL acetonitrile was stirred at r.t. for 4h under 02 at atmospheric pressure. GC analysis (3-chloro-benzaldehyde as internal standard) revealed 3-cyanobenzaldehyde in 98% yield. Flash column chromatography on silica gel yielded 2.8 mmol of pure 3-cyanobenz-aldehyde (m.p. 77-78 °C 93 % yield). 

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