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1.
The ability of DNA to extract fluoroquinolones from model solutions and real probes of food was demonstrated and investigated
quantitatively. The interaction between fluoroquinolones and different types of DNA was studied by equilibrium dialysis. The
first application of this direct approach allowed us to determine binding constants and binding stoichiometries in different
conditions. The binding of enrofloxacin to heat-denatured DNA (d-DNA) from herring sperm is pH- and magnesium-dependent; the
highest fraction of bound drugs was found at pH 7 and a magnesium concentration of 0.5–1 mM. Results for three types of DNA:
d-DNA, double-stranded DNA and single-stranded DNA were compared. The unwound DNA showed almost doubled binding constants
and stoichiometries, thus indicating preferable interaction of enrofloxacin with single-strand regions of DNA. The binding
of other fluoroquinolones (lomefloxacin, ciprofloxacin, norfloxacin, danofloxacin and sarafloxacin) with d-DNA is very similar
to that of enrofloxacin: the binding constants are in the range from 0.94 × 105 to 2.40 × 105 M−1, and the stoichiometries range from 4.1 to 6.9 fluoroquinolone molecules per 100 DNA bases. The binding properties were quantitatively
the same for extraction of fluoroquinolones from model aqueous solutions and from liquid food (milk). The results indicate
the efficiency of DNA for selective extraction of fluoroquinolones from real samples for further analysis. This selective
binding also allows us to consider DNA as a natural receptor for development of analytical techniques for fluoroquinolones. 相似文献
2.
A. Markwitz H. Baumann E. F. Krimmel K. Bethge P. Misaelides 《Fresenius' Journal of Analytical Chemistry》1993,346(1-3):177-180
Summary Thin, amorphous silicon nitride (a-SINx) films were deposited on n-type (100) silicon substrates using an argon ion beam for sputtering a HPSN block under high vacuum conditions. The substrates were kept at room temperature. Nitrogen depth distributions were determined by NRA using the resonance reaction 15N(p,)12C at 429 keV. Hydrogen profiles were analysed by NRA (1H(15N,)12C at Eo=6.385 MeV) and by ERDA (20Ne2+, Eo=10 MeV). The NRA was used to determine the depth distributions (concentration vs. areal density) of nitrogen and hydrogen taking calibration standards into consideration. The silicon depth distributions and the N/Si ratios of the deposited a-SiNx films were determined by RBS (4He+, Eo=2.0 MeV). Film thicknesses were obtained by SEM. The density of the deposited a-SiNx films was found to be =2.7 (±0.1) g/cm3 by correlating RBS data and real film thicknesses as obtained by SEM. 相似文献
3.
Guillaume Chalumot Cong YaoVerónica Pino Jared L. Anderson 《Journal of chromatography. A》2009,1216(27):5242-5248
The complexation of native β-cyclodextrin (CD) and seven aromatic compounds, namely, phenetole, toluene, m-xylene, naphthalene, biphenyl, fluorene and phenanthrene, has been studied for first time utilizing a solid-phase microextraction (SPME)–high-performance liquid chromatography (HPLC) method. The stoichiometries of the analyte:β-CD complexes were found to be either 1:1 or 1:2. The formation of 1:2 complexes was confirmed for naphthalene, biphenyl, fluorene, and phenanthrene only when utilizing relatively high concentrations of β-CD (up to 6.6 mM). The 1:2 stoichiometries were confirmed using the classical modified Benesi–Hildebrand (BH) method. The calculated binding constants for 1:1 stoichiometries (K1) using the SPME method varied from 115.3 M−1 for toluene to 3510 M−1 for phenanthrene, whereas the corresponding values to the 1:2 stoichiometries (K3) varied from 7.30 × 105 M−2 for biphenyl to 9.03 × 106 M−2 for naphthalene. 相似文献
4.
Andreas Markwitz Horst Baumann Rolf W. Michelmann Jörg D. Meyer Eberhard F. Krimmel Klaus Bethge 《Mikrochimica acta》1997,125(1-4):337-341
Thin silicon nitride (SiN
x
) layers with the stoichiometric N/Si ratio of 1.33 in the maximum of the concentration depth distributions of nitrogen were produced by implanting 10 keV15N
2
+
in 100 silicon at room temperature under high vacuum conditions. The depth distribution of the implanted isotope was measured by resonance nuclear reaction analysis (NRA), whereas the layer structure of the implanted region and the geometrical thickness of the layers were characterised by high resolution transmission electron microscopy (TEM). SiN
x
layers with a thickness of about 30 nm were determined by NRA. Channeling Rutherford backscattering spectrometry was used to determine the disorder in the silicon substrate. Sharp interfaces of a few nanometers between the highly disordered implanted region and the crystalline structure of the substrate thickness were observed by TEM. The high thermal stability of SiN
x
layers with N/Si ratios from under to over stoichiometric could be shown by electron beam rapid thermal annealing (1100 °C for 15 s, ramping up and down 5 °C/s) and NRA. 相似文献
5.
Junichiro Sameshima Aya Takenaka Yuichi Muraji Shingo Ogawa Masanobu Yoshikawa Katsuaki Suganuma 《Surface and interface analysis : SIA》2019,51(7):743-753
To examine precise depth profiles at the interface of SiO2/SiC, a high resolution that can detect slight discrepancies in the distribution is needed. In this study, an experimental method to achieve a high resolution of less than 1 nm was developed by using dual-beam time-of-flight secondary ion mass spectrometry (TOF-SIMS). The analysis was preceded by the following three steps: (1) determination of the optimal analytical conditions of the analysis beam (Bi+) and sputtering beam (Cs+), (2) verification of the etching methods to thin the SiO2 layer, and (3) confirmation of the benefits of the low-energy sputtering beam directed toward SiO2/SiC samples. By using the secondary ion intensity peak-to-valley ratio of BN− and BO− of a sample with delta-doped boron multilayers, the appropriate Bi+/Cs+ condition for a high depth resolution was determined for each energy level of the sputtering beam. Upon verification of the etching methods to thin the SiO2 layer, slight discrepancies were found between samples that were obtained with different etching methods. The difference in the roughness values of the etched surfaces was proactively utilized for the performance confirmation of the low-energy sputtering beam by means of precise observation of the profiles at the SiO2/SiC interface. The use of a Cs beam with a low energy between 0.25 and 0.5 keV enabled the detection of slight discrepancies in the roughness of less than 1 nm between samples. The aforementioned method has the potential to accurately detect discrepancies in the intrinsic distribution at the SiO2/SiC interface among samples. 相似文献
6.
A. Markwitz H. Baumann W. Grill B. Heinz A. Röseler E. F. Krimmel K. Bethge 《Fresenius' Journal of Analytical Chemistry》1995,353(5-8):734-739
Homogeneous ultra thin silicon nitride layers (SiNx layers) close to the surface have been produced by 10 keV 15N
2
+
molecular ion implantation and an ion current density of 10 A/cm2, into single crystal silicon at room temperature. Stoichiometric SiNx layers with thicknesses of about 28 nm (analyzed by NRA) were obtained at fluences of 1.5×1017 at/cm2. NRA analyses of samples annealed by EB-RTA at T=1150° C for 15 s indicated that the N/Si ratio and the layer thickness did not change drastically. FT IR ellipsometry analyses indicated the existence of Si3N4 bonds in as-implanted specimens. A disordered Si layer (d-Si, typically 15 nm thick) underneath the implantation region caused by the ion implantation was found by channeling RBS analyses. The d-Si layer partly recrystallized during EB-RTA showing a thickness of 6 nm afterwards. The SiNx layers showed no decomposition and detachment after EB-RTA. Due to EB-RTA, however, the smooth surface of the as-implanted specimens changed into a surface with remaining whisker-like structures surrounded by circular recesses as shown by AFM analyses. A model for the growth of these whisker-liker structures caused by low energy ion implantation and EB-RTA is presented on the basis of the thickness of the SiNx layer, the existence of the d-Si layer and the special annealing process. 相似文献
7.
Romana Mikšová Pavel Horák Václav Holý Anna Macková 《Surface and interface analysis : SIA》2019,51(11):1113-1120
A Si crystal layer on SiO2/Si was implanted using 0.4-MeV Kr+, Ag+, and Au+ at ion fluences of 0.5 × 1015 to 5.0 × 1015 cm−2. Subsequent annealing was performed at temperatures of 450° and 800° for 1 hour. The structural modification in a Si crystal influences ion beam channelling phenomena; therefore, implanted and annealed samples were investigated by Rutherford backscattering spectrometry under channelling (RBS-C) conditions using an incident beam of 2-MeV He+ from a 3-MV Tandetron in random or in aligned directions. The depth profiles of the implanted atoms and the dislocated Si atom depth profiles in the Si layer were extracted directly from the RBS measurement. The damage accumulation and changes in the crystallographic structure before and after annealing were studied by X-ray diffraction (XRD) analysis. Lattice parameters in modified silicon layers determined by XRD were discussed in connection to RBS-C findings showing the crystalline structure modification depending on ion implantation and annealing parameters. 相似文献
8.
《Spectrochimica Acta Part B: Atomic Spectroscopy》1998,53(10):1413-1420
This work evaluates the possibilities of applying microsecond-pulse glow discharge time of flight mass spectrometry (μs-pulse GD-TOFMS) in surface depth analysis. Investigations have been done for effects of discharge pressure on sputtered depth profiles as well as on topographies under μs-pulse GD mode; and also for influences of discharge current and discharge frequency on characteristics of sputtered surface. Sputtering rates of several pure metals under μs-pulse GD and dc-GD modes were studied and compared. The estimated erosion rates are 1.27, 2.90 and 5.18 nm s−1 for pure Fe, Cu and Zn layer, respectively. Depth profiling were conducted for a technical Zn–Fe layer (about 10 μm) and for a Fe–Cu layer (about 1 μm) by μs-pulse GD. A simple model was developed and utilized to convert ion intensity into element concentration, and the experimental results were presented and discussed. Preliminary results show that μs-pulse GD-TOFMS has a promising future in the area of surface depth analysis, especially in the depth analysis of thin layers and of their cross-sections. 相似文献
9.
A. Baron Wiecheć A. Tempez P. Skeldon P. Chapon G. E. Thompson 《Surface and interface analysis : SIA》2012,44(10):1346-1352
A comparison is made between plasma profiling time‐of‐flight mass spectrometry (PP‐TOFMS) and nuclear reaction analysis (NRA) for depth profiling of 18O tracer in porous anodic oxide films on aluminum. The films were formed galvanostatically, for a range of times, using phosphoric acid electrolytes that were either enriched in 18O or of the natural isotopic concentration. The morphologies of the films were determined by electron microscopy. The findings from PP‐TOFMS and NRA reveal a partitioning of the tracer between the surface regions and buried layers of the films. However, a relatively high background of 16O in PP‐TOFMS prevents a reliable quantification of the concentration of 18O. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
10.
The accuracy of ultrashallow depth profiling was studied by secondary ion mass spectrometry (SIMS) and high‐resolution Rutherford backscattering spectroscopy (HRBS) to obtain reliable depth profiles of ultrathin gate dielectrics and ultrashallow dopant profiles, and to provide important information for the modeling and process control of advanced complimentary metal‐oxide semiconductor (CMOS) design. An ultrathin Si3N4/SiO2 stacked layer (2.5 nm) and ultrashallow arsenic implantation distributions (3 keV, 1 × 1015 cm?2) were used to explore the accuracy of near‐surface depth profiles measured by low‐energy O2+ and Cs+ bombardment (0.25 and 0.5 keV) at oblique incidence. The SIMS depth profiles were compared with those by HRBS. Comparison between HRBS and SIMS nitrogen profiles in the stacked layer suggested that SIMS depth profiling with O2+ at low energy (0.25 keV) and an impact angle of 78° provides accurate profiles. For the As+‐implanted Si, the HRBS depth profiles clearly showed redistribution in the near‐surface region. In contrast, those by the conventional SIMS measurement using Cs+ primary ions at oblique incidence were distorted at depths less than 5 nm. The distortion resulted from a long transient caused by the native oxide. To reduce the transient behavior and to obtain more accurate depth profiles in the near‐surface region, the use of O2+ primary ions was found to be effective, and 0.25 keV O2+ at normal incidence provided a more reliable result than Cs+ in the near‐surface region. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
11.
《Surface and interface analysis : SIA》2003,35(10):829-834
The implantation of a high dose of high‐energy ions into an Si wafer causes amorphization of the original monocrystalline structure within a near‐surface layer. The in‐depth distribution of both Si atoms of the wafer and As ions implanted at a dose of 1 × 1017 ions cm?2 and an energy of 100 keV is studied. A novel method combining a repeated planar and broad sputter etching with differential weighing, surface analysis by total reflection x‐ray fluorescence and Tolansky interferometry is used for this investigation. Different depth profiles are recorded on the nanometre scale for the concentration defined as the mole ratio of As and Si, for the mass density of the implanted layer and for the number density of As and Si. The results generally correspond with measurements of Rutherford backscattering spectrometry and only deviate when the assumptions made for the mass density do not fit well. An appropriate approach to this quantity involves the number density of implanted ions but, furthermore, considers a variation of the number density of Si atoms during implantation, especially for a high dose and high‐energy implantation. The variation can be taken into account by a factor γ, where γ > 1 indicates compression and γ < 1 indicates extension of the original crystalline structure. For the above mentioned implantation, γ is measured separately for each sublayer to obtain accurate depth profiles. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
12.
《Journal of Coordination Chemistry》2012,65(13):2351-2366
The structure and stoichiometries of the complexes that could be formed between Cu2+ and 3,4-dihydro-3-(2-oxo-2-phenylethylidene)-quinoxalin-2(1H)-one (1) were investigated by various spectral techniques such as IR, fluorescence, UV–vis and electron paramagnetic resonance. The results suggest that initially 3?:?1 and 2?:?1 (1/Cu2+) complexes are formed at low Cu2+ concentration and upon adding more Cu2+, 1?:?1 (preferred) and 1?:?2 complexes are generated. Since 1 possesses two possible binding sites, further exploration was done by testing the binding ability of Cu2+ to fragments of 1, namely β-enaminoketone derivatives (2–3) and quinoxaline-2-one (4), and by executing calculations of thermodynamic parameters of the reaction between 1 and Cu2+ in ethanol, optimized geometries of the possible complexes, and estimation of stability constants at various stoichiometries. Consequently, a step-by-step binding mechanism is suggested for formation of various complexes between 1 and Cu2+. 相似文献
13.
H. Bubert 《Mikrochimica acta》1986,90(5-6):387-406
The physical and chemical prerequisites of ion implantation and their translation into a Monte Carlo calculation simulating the implantation process of high energy ions (300 keV) are described; calculations are extended to high dose implantation (up to 1×1018 ions cm–2) taking into consideration various effects such as matrix change during implantation, cascade mixing, sputter erosion and relaxation of the target material.To check the suitability of such calculations for a characterization of implanted samples, the results of the calculations are compared with those obtained experimentally from implanted samples. As an example,P
+ is implanted into polycrystalline Al at various doses (110×1017
p
+ cm–2), and depth profiles are taken by AES/Ar+-sputtering.The calculated and measured results agree better than 10% for both the depth and the concentration scale. 相似文献
14.
Seawater samples were collected from the East China Sea continental shelf and analyzed for 239+240Pu activities. The vertical profiles of 239+240Pu had a similarity for all three stations in the East China Sea. 239+240Pu concentrations were low in the surface layer (3-4 mBq/m3) and increased gradually with depth to become high in the near-bottom layer (7-10 mBq/m3). 239+240Pu concentrations in seawater and the concentrations of suspended particles showed almost the same vertical profiles in the East China Sea continental shelf. The maximum value of 239+240Pu found in the near-bottom layer may be due to the contribution of Pu-rich suspended particles. 相似文献
15.
New horizons in sputter depth profiling inorganics with giant gas cluster sources: Niobium oxide thin films
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Ashley A. Ellsworth Christopher N. Young William F. Stickle Amy V. Walker 《Surface and interface analysis : SIA》2017,49(10):991-999
X‐ray photoelectron spectroscopy is used to study a wide variety of material systems as a function of depth (“depth profiling”). Historically, Ar+ has been the primary ion of choice, but even at low kinetic energies, Ar+ ion beams can damage materials by creating, for example, nonstoichiometric oxides. Here, we show that the depth profiles of inorganic oxides can be greatly improved using Ar giant gas cluster beams. For NbOx thin films, we demonstrate that using Arx+ (x = 1000‐2500) gas cluster beams with kinetic energies per projectile atom from 5 to 20 eV, there is significantly less preferential oxygen sputtering than 500 eV Ar+ sputtering leading to improvements in the measured steady state O/Nb ratio. However, there is significant sputter‐induced sample roughness. Depending on the experimental conditions, the surface roughness is up to 20× that of the initial NbOx surface. In general, higher kinetic energies per rojectile atom (E/n) lead to higher sputter yields (Y/n) and less sputter‐induced roughness and consequently better quality depth profiles. We demonstrate that the best‐quality depth profiles are obtained by increasing the sample temperature; the chemical damage and the crater rms roughness is reduced. The best experimental conditions for depth profiling were found to be using a 20 keV Ar2500+ primary ion beam at a sample temperature of 44°C. At this temperature, there is no, or very little, reduction of the niobium oxide layer and the crater rms roughness is close to that of the original surface. 相似文献
16.
W. Theodossiu H. Baumann A. Markwitz K. Bethge 《Fresenius' Journal of Analytical Chemistry》1995,353(3-4):483-486
SiCx layers close to the surface have been produced by implanting 40 keV 13C ions into silicon with a fluence of 6 × 1017 at./cm2 (j = 12 A/cm2) at room temperature (RT). Depth distributions and areal densities (doses) of the implanted carbon have been analysed by the nuclear reaction 13C(p,)14N (NRA) which shows a sharp resonance in the excitation function at a proton energy of 1748 keV (G = 75 eV FWHM). The depth resolution at the surface amounts to 31 nm due to energy spread of the proton beam (1.2 keV FWHM) and resonance width. The surface resolution of the NRA can be increased up to 8 nm when tilting the sample (surface normal) to an angle of 75° with respect to the proton beam direction. Using a NaI detector the detection limit of 13C in silicon is approximately 1 at.%. Comparative elastic backscattering measurements with 4He+ projectiles were performed at 2 MeV (Rutherford backscattering spectroscopy, RBS) and 3.45 MeV (high energy backscattering, HEBS) at a backscattering angle of 171°. The measured 13C depth distributions have been compared with a distribution calculated by the Monte Carlo algorithm T-DYN. 相似文献
17.
R. Valledor J. Pisonero N. Bordel J. I. Martín C. Quirós A. Tempez A. Sanz-Medel 《Analytical and bioanalytical chemistry》2010,396(8):2881-2887
Nanometer depth resolution is investigated using an innovative pulsed-radiofrequency glow discharge time-of-flight mass spectrometer
(pulsed-rf-GD-TOFMS). A series of ultra-thin (in nanometers approximately) Al/Nb bilayers, deposited on Si wafers by dc-magnetron
sputtering, is analyzed. An Al layer is first deposited on the Si substrate with controlled and different values of the layer
thickness, t
Al. Samples with t
Al = 50, 20, 5, 2, and 1 nm have been prepared. Then, a Nb layer is deposited on top of the Al one, with a thickness t
Nb = 50 nm that is kept constant along the whole series. Qualitative depth profiles of those layered sandwich-type samples are
determined using our pulsed-rf-GD-TOFMS set-up, which demonstrated to be able to detect and measure ultra-thin layers (even
of 1 nm). Moreover, Gaussian fitting of the internal Al layer depth profile is used here to obtain a calibration curve, allowing
thickness estimation of such nanometer layers. In addition, the useful yield (estimation of the number of detected ions per
sputtered atom) of the employed pulsed-rf-GD-TOFMS system is evaluated for Al at the selected operating conditions, which
are optimized for the in-depth profile analysis with high depth resolution. 相似文献
18.
Clara Turetta Carlo Barbante Gabriele Capodaglio Andrea Gambaro Paolo Cescon 《Microchemical Journal》2010,96(2):194-202
Vertical profiles for total dissolved thallium were obtained at five sites in the western sector of the Ross Sea (Southern Ocean), Antarctica. Thallium is estimated to have a natural mean seawater concentration between 50 and 65 pmol L− 1 with higher values in the North Pacific (65 ± 5 pmol L− 1) and lower in the Bay of Biscay and Irish Sea (49 ± 3 pmol L− 1). Our samples show a concentration varying from 22 to 55 pmol L− 1 with a mean value of 46 pmol L− 1, depending on depth, dissolved oxygen, salinity and local topographic characteristics. The analyses were performed using an ICP-SFMS that has enabled us to obtain reliable Tl concentration measurements with a relative standard deviation of better than 2.5% and a detection limit, calculated as three times the standard deviation of the “blank signal” of 0.69 pmol L− 1 (1.60 pmol L− 1, obtained analysing four blank solutions (n = 5) prepared with the same water and acid used for the dilution/acidification steps). Thallium appears to have a nearly conservative distribution in seawater as highlighted also from the comparison with the profiles of two seawater conservative elements: molybdenum and uranium; however it also highlights the presence of a reactive component of thallium, which is more influenced by the presence of particulate matter, oxygen content and fluorescence. 相似文献
19.
New host molecules for anions, adamantane, and alkyl urea derivatives substituted by naphthalene chromophores, were synthesized. Their binding with F−, Cl−, Br−, OAc−, HSO4−, NO3−, and H2PO4− was investigated by UV-vis, fluorescence and NMR spectroscopy. The anion binding ability of adamantyl bisurea derivatives was compared with the analogous host molecules, wherein the urea moieties are separated by flexible alkyl linkers of the same length, and adamantane monourea derivative. The host molecules show the highest selectivity toward F− and H2PO4−. The binding stoichiometry and the values of the association constants depend on the basicity of anions, availability of H-bonding sites, preorganization, and rigidity of the hosts, as well as solvent polarity and H-bonding availability. Rigid adamantane receptors, compared to flexible analogues show increased selectivity for H2PO4−, whereas binding of OAc− is better with flexible receptors. The binding of OAc− and H2PO4− was investigated by microcalorimetry. The stoichiometries and the stability constants of the corresponding complexes obtained by this method were in good agreement compared to those determined by UV-vis titrations. In both cases the enthalpic contribution to the overall complex stability was predominant. 相似文献
20.
An analytical procedure for precisely determining the stoichiometry of NaxCoO2-type superconductor material is presented. Sodium and cobalt contents, ranging between 3.5 and 11 mg L−1 and 18 and 32 mg L−1, respectively, were measured simultaneously using CID–ICP–OES. Sodium was found to significantly lower the emission intensity
of cobalt, so the addition of 6.4 g L−1 of the ionization buffer LiCl was required to compensate for this effect. The recoveries and precisions of the measurements
were significantly increased by internal standardization using yttrium: Co(II) emission intensities at 230.786 nm, 237.862 nm,
and 238.346 nm can be corrected using Y ion emission intensities, as can the atomic emissions of Co at 345.351 nm and Na at
589.592 nm. The cobalt contents of three real superconductor samples were independently verified by complexometric titration
using EDTA. The valence state of cobalt was determined with a relative uncertainty of ~0.5% by redox titration using sodium
oxalate as reductive agent and Ce(SO4)2 solution. The final stoichiometries of the superconductor samples can be calculated using the Na and Co contents, and the
Co valence state. Conclusions about the quality of the prepared samples in terms of phase purity and presence of side products
are drawn. 相似文献