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171.
The analysis of conductive solid samples by r.f. capacitively coupled plasma at atmospheric pressure
Anghel SD Frentiu T Rusu AM Bese L Cordos EA 《Analytical and bioanalytical chemistry》1996,355(3-4):252-253
A radiofrequency capacitively coupled plasma (rf CCP) with tip-ring electrode geometry has been used for the analysis of Al, Co, Cr, Cu, Mn, Mo, Ni, and V in low and medium alloyed steel. The sample is used as one of the electrodes of the plasma torch. The influence of plasma power, argon flow rate and distance between the electrodes on the analytical signals has been studied. The limits of detection are in the range of 0.001 to 0.048%. The dynamic range is three orders of magnitude. 相似文献
172.
Frenţiu T Rusu AM Ponta M Anghel SD Cordos EA 《Analytical and bioanalytical chemistry》1996,355(3-4):254-255
A low to medium power radiofrequency capacitively coupled plasma is characterized as spectral source for atomic emission. The signal to background ratio and the limits of detection were determined for 19 elements as a function of the plasma torch geometry and the observation point. 相似文献
173.
Mihai Horn Sorin Mager Nicolae Palibroda Monica Culea 《Journal of mass spectrometry : JMS》1991,26(7):649-652
Electron impact-induced fragmentations of 2-substituted 5,5-bis(carboethoxy)-l,3-dioxanes were studied by exact mass measurements and metastable ion analysis. The substituent R on C(2) of the heterocyclic ring has little influence on the principal cleavage reactions. Elimination of CH2O/CO and C2H4O/C2H4/C2H5OH are common fragmentations for ions containing the 1,3-dioxane moiety or the OC2H5 group, respectively. The abundant ions at m/z 173 and 127 serve as structural probes for the class of compounds studied. Primary fragmentations implying the ester function are of little importance. 相似文献
174.
The structure of 2-diethylamino-6-methyl-5-n-propyl-4(3H)-pyrimidinone has been studied by X-ray crystallography and quantum-chemical calculations. X-ray analysis established that 2-diethylamino-6-methyl-5-n-propyl-4(3H)-pyrimidinone exists exclusively as the lactam tautomer protonated at the N3 ring nitrogen in the solid state. Crystals of 2-diethylamino-6-methyl-5-n-propyl-4(3H)-pyrimidinone are monoclinic (space group P21/n); the unit-cell dimensions are: a = 11.0460(8) Å, b = 5.0064(4) Å, c = 22.8358(17) Å, = = 90°, = 90.521(1)°. In the crystal, molecules of 2-diethylamino-6-methyl-5-n-propyl-4(3H)-pyrimidinone are assembled in planar centrosymmetric dimers by strong resonance-assisted N—H···O intermolecular hydrogen bonds from the NH group of one molecule to the C=O of the adjacent molecule (N—H···O distance 2.804 Å). Bond distances and angles are generally similar to those reported for the corresponding tautomer of isocytosine and derivatives. Quantum-chemical calculations on 2-diethylamino-6-methyl-5-n-propyl-4(3H)-pyrimidinone are also reported in order to estimate the relative energies of the possible tautomeric forms; ab initio and DFT results predict the coexistence of the N3 and AH tautomers in the gas phase. There is excellent correspondence between the crystal and the HF/6-311G** or B3LYP/6-31G* calculated structures of the N3 lactam form; the largest deviations between the experimental and computed structures are mostly the effects of strong intermolecular H bonds in the crystal. 相似文献
175.
S Sorin 《Journal of Mathematical Analysis and Applications》1984,98(1):296-303
For each p in the simplex P of k we introduce convex subsets of P, ΠI(p) and ΠII(p). For f a real function on P we define Cav1f to be the smallest function greater than f on P and concave on Π1(p) for each p in P (and similarly VexIIf). Given u a continuous real function on P we prove that the following problems: have the same solution which is also the only solution of f = Vex11 max{u,f} = Cav1 min{u,f}. This is an extension of a former proof by Mertens and Zamir for the case where P is a. product of convex R and S with ΠI(p) = r × S and ΠII(p) = R × s. 相似文献
176.
Sorin Mager Ruxandra TĂranu Mihai Horn Mariana Mureşan 《Monatshefte für Chemie / Chemical Monthly》1982,113(5):565-572
Mono and dispiro-1,3-dioxanes (1–3) were synthesized by the condensation of 1,2-, 1,3- and 1,4-cyclohexanedione, respectively (4–6) with bis-(hydroxymethyl)-malonic ester (7). The1H-NMR spectra prove for the mono- (2) and dispiro-1,3-dioxane (3) the existence of conformational equilibria and for the monospiro-1,3-dioxane (1) a “fixed” structure. C6D6 causes a remarkable solvent shift effect in the NMR spectra separating a superposed complex coupling pattern (in CDCl3) in two well resolved AB doublets and two AX quartets. TheE-oxime of the monospiro-1,3-dioxanone (1) represents also a “fixed” structure. Bis-(hydroxymethyl)-malonic ester (7) is a formaldehyde generating agent in the condensation reaction of dimedone with the diol7. 相似文献
177.
178.
Effects of Grafting Density and Film Thickness on the Adhesion of Staphylococcus epidermidis to Poly(2‐hydroxy ethyl methacrylate) and Poly(poly(ethylene glycol)methacrylate) Brushes 下载免费PDF全文
Sorin‐Alexandru Ibanescu Justyna Nowakowska Nina Khanna Regine Landmann Harm‐Anton Klok 《Macromolecular bioscience》2016,16(5):676-685
Thin polymer films that prevent the adhesion of bacteria are of interest as coatings for the development of infection‐resistant biomaterials. This study investigates the influence of grafting density and film thickness on the adhesion of Staphylococcus epidermidis to poly(poly(ethylene glycol)methacrylate) (PPEGMA) and poly(2‐hydroxyethyl methacrylate) (PHEMA) brushes prepared via surface‐initiated atom transfer radical polymerization (SI‐ATRP). These brushes are compared with poly(ethylene glycol) (PEG) brushes, which are obtained by grafting PEG onto an epoxide‐modified substrate. Except for very low grafting densities (ρ = 1%), crystal violet staining experiments show that the PHEMA and PPEGMA brushes are equally effective as the PEG‐modified surfaces in preventing S. epidermis adhesion and do not reveal any significant variations as a function of film thickness or grafting density. These results indicate that brushes generated by SI‐ATRP are an attractive alternative to grafted‐onto PEG films for the preparation of surface coatings that resist bacterial adhesion.
179.
Numerical approximation of the boundary control for the wave equation with mixed finite elements in a square 总被引:1,自引:0,他引:1
180.
A new simple, sensitive and selective liquid chromatography coupled with mass spectrometry (LC/MS) method for quantification of tramadol and its active metabolite O-desmethyltramadol in human plasma was validated. The tramadol and its metabolite were separated on a reversed phase column (Zorbax SB-C18, 100 mm x 3.0 mm I.D., 3.5 microm) under isocratic conditions using a mobile phase of a 10:90 (v/v) mixture of acetonitrile and 0.2% (v/v) trifluoroacetic acid in water. The flow rate was 1 ml/min at the column temperature 45 degrees C. In these chromatographic conditions, the retention times were 2.3 min for O-desmethyltramadol and 3.5 min for tramadol, respectively. The detection of both analytes was in SIM mode using an ion trap mass spectrometer with electrospray positive ionisation. The monitored ions were m/z 264 for tramadol and m/z 250 for its metabolite. The sample preparation was very simple and rapid and consisted in plasma protein precipitation from 0.2 ml plasma using 0.2 ml solution of perchloric acid 7%. Calibration curves were generated over the range of 2-300 ng/ml for both analytes with values for coefficient of correlation greater than 0.998 and by using a weighted (1/y) quadratic regression. The values of precision and accuracy for tramadol at quantification limit were less than 10.9% and 5.1, respectively, both for within- and between-run. For O-desmethyltramadol, precision and accuracy at quantification limit were 10.1% and -9.9% for within-run determinations and 6.7% and 10.4% for between-run determinations, respectively. The mean recovery for both analytes was 96%. Both tramadol and its metabolite demonstrated good short-term, long-term, post-preparative and freeze-thaw stability. This is the first reported method for analysis of tramadol and O-desmethyltramadol in human plasma that uses protein precipitation as sample processing procedure. The method is very simple and allows obtaining a very good recovery of both analytes. The validated LC/MS method has been applied to a pharmacokinetic study of 50 mg tramadol tablets on healthy volunteers. 相似文献