Determination of the enantiomers of fenoldopam in human plasma by reversed-phase high-performance liquid chromatography after chiral derivatization.

Fenoldopam, a selective agonist at peripheral dopaminergic (DA-1) receptors, is administered as a racemic mixture and, consequently, an indirect stereospecific high-performance liquid chromatographic assay was developed to study the disposition of the individual enantiomers in human subjects. Fenoldopam enantiomers were extracted from alkalinized plasma into ethyl acetate prior to precolumn derivatization with the chiral reagent 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate (GITC). The resulting diastereomers were separated on a reversed-phase butylsilica column and determined using triple-electrode coulometric detection. The limits of determination and detection for the S- and R-enantiomers of fenoldopam were 0.5 and 0.25 ng/ml, respectively. A linear response was observed for (S)- and (R)-fenoldopam concentrations ranging from 0.5 to 50 ng/ml in plasma. The intra-day relative standard deviations (R.S.D.s) for the plasma assay at nominal concentrations of 0.5, 5 and 50 ng/ml were 17.4, 5.2 and 6.9%, respectively, for (S)-fenoldopam and 9.9, 6.2 and 7.4%, respectively, for (R)-fenoldopam. The inter-day R.S.D.s of the method at these concentrations were 9.3, 7.7 and 7.4%, respectively, for (S)-fenoldopam and 9.5, 1.9 and 7.3%, respectively, for (R)-fenoldopam. The mean accuracy of the method at concentrations of 0.5, 5 and 50 ng/ml in plasma was found to be 106.4, 111.8 and 108.9%, respectively, for (S)-fenoldopam and 116.2, 104.2 and 111.2%, respectively, for (R)-fenoldopam. The assay developed was sufficiently sensitive, accurate and precise to support pharmacokinetic studies in human subjects.     

Microanalysis of perfluoro compounds

Summary Because of the extremely high thermal and chemical stability of perfluoro organic compounds, special methods of analysis are required for carbon, hydrogen and fluorine. Sulfur, phosphorus, and halogens can be determined by conventionalCarius digestion and subsequent gravimetric methods. Nitrogen is determined by theDumas method. Oxygen cannot be determined by the usualUnterzaucher method.Carbon and hydrogen are determined by combustion in oxygen with a tube filling consisting of (Ag; 3 MgO · Al₂O₃; Ag) at 950° C; (Ag; Pb₂O₃) at 450° C; (Ag;PbO₂;Ag) at 180° C. The sample burner is operated at 950° to 1000° C.Fluorine is determined by reaction with sodium in a conventional sodium peroxide bomb with lead or copper gasket. The lower part of the bomb is held at red heat with a torch for about 20 seconds. The sodium fluoride from the reaction is titrated with thorium nitrate.

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Zusammenfassung Für die Bestimmung von Kohlenstoff, Wasserstoff und Fluor in organischen perfluorierten Verbindungen sind wegen deren außerordentlich hoher thermischer und chemischer Stabilität spezielle analytische Methoden notwendig. Schwefel, Phosphor und die Halogene können nachCarius bzw. mit den üblichen gravimetrischen Methoden bestimmt werden. Sauerstoff kann nicht nach derUnterzaucher- Methode bestimmt werden.Kohlenstoff und Wasserstoff sind bestimmbar bei Verbrennung mit einer Rohrfüllung aus (Ag; 3 MgO · Al₂O₃; Ag) bei 900°; (Ag; Pb₂O₃) bei 450°: (Ag; PbO₂; Ag) bei 180°. Der bewegliche Brenner wird auf einer Temperatur von 950° bis 1000° gehalten.Fluor kann durch Umsetzung mit Natrium in einer gewöhnlichen Peroxyd-Bombe mit Blei- oder Kupfer-Dichtung bestimmt werden. Der untere Teil der Bombe wird mit einem Gebläse für 20 Sekunden auf Rotglut erhitzt. Das gebildete Natriumfluorid wird in der gewöhnlichen Weise mit Thoriumnitrat titriert.

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Résumé La grande stabilité thermique et chimique des composés organiques perfluorés impose l'emploi de méthodes spéciales pour le dosage du carbone, de l'hydrogène et du fluor. Il est possible de déterminer le soufre, le phosphore, et les halogènes par digestion classique deCarius suivie d'un dosage gravimétrique approprié. L'azote est dosé par la méthode deDumas; quant à l'oxygène, il ne peut être déterminé par la méthode habituelle deUnterzaucher.Le carbone et l'hydrogène sont déterminés par combustion dans l'oxygène à l'intérieur d'un tube comportant un remplissage constitué par (Ag; 3 MgO · Al₂O₃; Ag) à 950°, (Ag; Pb₂O₃) à 450° (Ag; PbO₂; Ag) à 180° C. Le brûleur mobile permet d'obtenir une température de 950 à 1000° C.Le fluor est dosé après minéralisation par le sodium dans une bombe courante à peroxyde de sodium, comportant un joint de plomb ou de cuivre. La partie inférieure de la bombe est portée au rouge à l'aide d'un chalumeau pendant environ 20 secondes. Le fluorure de sodium obtenu est titré à l'aide de nitrate de thorium.

     

Solution Polymerization of Acrylonitrile Catalyzed by Sodium Triethylthioisopropoxyaluminate: A Polyacrylonitrile with High Structural Regularity

A new catalyst for the polymerization of acrylonitrile has been found by reacting sodium aluminum tetraethyl with a stoichiometric amount of oxygen, alcohols, or mercaptans, etc. The catalyst prepared by reacting NaAlEt₄ with RSH remains active at temperatures as low as ?78°C., polymerizing acrylonitrile into high molecular weight polymers with high conversions. At ?78°C., the propagating chain remains active over a period of days, and the chain length increases with time or conversion. At high conversions the molecular weight of the polymer is directly proportional to the concentration of the monomer, the catalyst concentration being kept constant. The efficiency of the catalyst expressed as the ratio of the number of the polymer molecules produced to the number of the sulfur atoms used is in excess of 80%. The weight-average molecular weight of the polymer measured by light scattering is roughly equal to the number-average molecular weight determined by sulfur analysis assuming only onesulfur atom in each polymer molecule. Although the data given here are only qualitative in nature, it is nevertheless evident that this system bears great resemblances to anionic polymerizations resulting in “living polymers.” The polymer obtained with the NaAlEt₃S(i-Pr) catalyst at ?78°C. differs from free-radical polyacrylonitrile in exhibiting substantially lower solubility, higher melting point, and higher rate of crystallization than that for the free-radical polymer. The polymer is also free from structural mpurities; it does not cause fluorescence in dilute solutions and has no absorption peak at 265 mμ; both these effects are produced by impurities in free-radical polyacrylonitrile. It is concluded that the polymer reported here is more regular in structure than free-radical polyacrylonitrile.     

Impedance measurements on purified silver chloride crystals using ionic vs. electronic contacts

Impedance measurements are made on purified silver chloride crystals covering thicknesses from 0.064 cm to 0.400 cm at temperatures from 293 K to 310 K using constant ionic strength solution contacts with varying silver ion concentrations. Results characterize the macroscopic transport properties from 10 kHz to 0.01 Hz and at d.c. Electrical relaxation times, τ_el, are independent of crystal thickness and bathing solution composition, but dependent on temperature. The resistive component of the impedance, R_∞, is linear with crystal thickness, δ, and the geometric capacitance, C_g, linear with δ^?1. In agreement with Macdonald's theory, R_∞ is equal to the d.c. resistance, R₀. This indicates rapid ion exchange at the surface and no Warburg diffusion. The dimensionless dielectric constant, calculated from C_g and the crystal dimensions, is 15.4. An average activation energy of 0.298 eV, indicative of vacancy transport is found. The parameter α in the equivalent non-ideal Cole-Cole representation is 0.96 indicating a narrow distribution of time constants. These results are compared with the electronic contact measurements typical to solid state physics. Higher values of resistivity and lower values of C_g and conductivity are found with graphite and vapor deposited silver. These differences were as large as 10%. Calculated dielectric constants at 10 kHz were 14.8 and 13.5, respectively, while the most recent published value is 11.14. These differences suggest that ionic solution contact measurements may give more reliable values because surface coverage is more nearly uniform on the molecular level.     

Interference of chlorofluorocarbon (CFC)‐containing inhalers with measurements of volatile compounds using selected ion flow tube mass spectrometry

Selected ion flow tube mass spectrometry (SIFT-MS) is a sensitive technique capable of measuring volatile compounds (VCs) in complex gas mixtures in real time; it is now being applied to breath analysis. We investigated the effect of inhalers containing chlorofluorocarbons (CFCs) on the detection and measurement of haloamines in human breath. SIFT-MS mass scans (MS) and selected ion monitoring (SIM) scans were performed on three healthy non-smoking volunteers before and after inhalation of the following medications: Combivent™ metered-dose inhaler (MDI) (CFC-containing); Ventolin™ MDI (CFC-free); Atrovent™ MDI (CFC-free), Beclazone™ MDI (CFC-containing); Duolin™ nebuliser. In addition, the duration of the persistence of the mass/charge ratios was measured for 20 h. Inhalers containing CFCs generated large peaks at m/z 85, 87, 101, 103 and 105 in vitro and in vivo, consistent with the predicted product ions of CFCs 12, 114 and 11. No such peaks were seen with Duolin™ via nebuliser, or CFC-free MDIs. We conclude that measurement of VCs, such as haloamines, with product ions of similar m/z values to the ions found for CFCs would be significantly affected by the presence of CFCs in inhalers. This issue needs to be accounted for prior to the measurement of VCs in breath in people using inhalers containing CFCs. Copyright © 2009 John Wiley & Sons, Ltd.     

Four-photon pressure-induced ionization of Xe by 351-nm radiation

The four-photon ionization of xenon gas at 351 nm is observed to be primarily pressure-induced. These observations indicate that the absorption occurs mainly through interaction with bound Xe₂ molecules. A three-photon near-resonance was found to enhance appreciably the cross-section for multiquantum ionization. The radiative lifetime of the resulting Xe¹₂ was determined to be τ_rad = 51 ns, implying only a partial mixing of the 0⁺_u and 1_u, 0^-_u states.     

Solar magnetic fields measurements with a magneto-optical filter

Summary The presence of a magnetic field at different levels inside the Sun has crucial implications for helioseismology. The solar oscillation observing program carried out since 1983 at Mt. Wilson with Cacciani magneto-optical filter (MOF) has recently been modified to acquire full-disk magnetograms with 2 arcsec spatial resolution. We present here a method for the correct determination of magnetic maps which are free of contamination by velocity signal. We show that no cross-talk exists between the Doppler and Zeeman shifts of the NaD lines, provided that instrumental polarization effects are taken into account. We also used the observed line-ofsight photospheric field to map the vector field in the inner corona, above active regions, in the ?current free? approximation.

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Riassunto La presenza di un campo magnetico a differenti livelli dell'interno solare ha importanti implicazioni nell'eliosismologia. Il programma osservativo a Mt. Wilson, in corso dal 1983 con il filtro magneto-ottico di Cacciani, è stato recentemente arricchito con l'acquisizione anche di mappe magnetiche. Si illustra la procedura di riduzione dei dati per una corretta determinazione dei campi magnetici e di velocità. Viene poi utilizzato il campo longitudinale fotosferico per ricostruire il campo magnetico vettoriale a livello coronale, al di sopra delle regioni attive, nell'approssimazione ?current free?.

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Резюме Налччие магнитного поля на различных уровнях внутри Солнца имеет существенное значение для гелиосейсмологии. Программа наблюдения солнечных осцилляций, проводимая с 1983 года на г. Вильсон с помощью магнитно-оптического фильтра, была недавно модифицирована. В этой работе мы предлагаем метод для определения магнитных карт, которые свободны от погрешностей, обусловленных сигналом скорости. Мы показываем, что при учете инструментальных эффектов поляризации, не существует связи между доплеровским и зеемановским сдвигами линий NaD. Мы также используем наблюдаемое поле фотосферы для отобразения векторного поля во внутренней короне, выше, активных областей.

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Paper presented at the 4th Cosmic Physics National Conference, Capri, September 11–14, 1988.

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To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

The influence of reorientational collisions on coherent optical processes

Numerical calculations of pulse transmission in SF₆ are performed to appraise the role of reorientational collisions. No support is found for the recent postutate calling for thermally equilibrated magnetic sublevels in self-induced transparency.