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31.
Summary Herein is reported an analytical solution to the peak broadening or peak dispersion/flattening equation based on the recently proposed Instrumental Spreading Shape Function and its application to correction for imperfect resolution (inadequate peak separation and/or excessive peak broadening) for higher molecular weight averages. The relationship of these higher MW averages with the familiar Weight Average and number average molecular weights is also discussed. Criteria for perfect resolution are specified and a true molecular weight calibration curve is accordingly defined. 相似文献
32.
Olle Nilsson 《Journal of separation science》1982,5(1):38-44
The total length-based second moment contribution from longitudinal sample diffusion in both phases on a column, σD , is derived by adding individual partial differential contributions to a partial differential equation accounting for the longitudinal diffusion processes only. Although each diffusion-dispersed sample part is equilibrated between two phases, the resulting σ,D (= 2D mt m + 2D st s) can be interpreted as the sum of two independent contributions in accordance with the variance addition rule. (D m and D s are the mean diffusion coefficients and t mand t s the mean residence times of the sample in the mobile and stationary phases, respectively.) The same σD expression is derived from the random walk model of Giddings by treating the diffusional process in each phase as statistically independent of the other processes. Under these conditions the broadening contribution from longitudinal diffusion in the mobile phase is shown to be independent of the velocity profile. 相似文献
33.
Summary We present a molecular theory of the energy distributions for the internal quantum states of a solute in a liquid or glassy solvent. We show that the energy distributions for different states are correlated in a way that depends on the solute-solvent interactions. We show how the theory can be modified easily to describe the transition-energy distributions for different pairs of states, which are of course related to inhomogeneously broadened absorption spectra. We also show that the distributions for different transitions are correlated, and describe how this correlation is measured by nonresonant fluorescence- and phosphorescence-line-narrowing and hole-burning experiments. The theory provides a microscopic framework within which to interpret different phenomenological models. For the case of a Lennard-Jones solute in a Lennard-Jones liquid solvent, we compare our theory to Monte Carlo simulation. 相似文献
34.
35.
Hans-Georg Schmarr Birgit Maas Armin Mosandl Stephan Bihler Hans-Peter Neukom Konrad Grob 《Journal of separation science》1991,14(5):317-321
An unusual peak defocusing effect influencing chromatographic performance over a limited range of elution temperatures is described for hexakis(2,6-di-O-pentyl-3-O-acetyl)-α-cyclodextrin stationary phase. Since this phenomenon is likely to be dependent on minor details of the cyclodextrin molecule, full assignment of the 1H- and 13C-NMR-spectra are given. 相似文献
36.
In on-column or in splitless injection with recondensation of the solvent, the length of the flooded zone in the column inlet depends primarily on the wettability of the internal wall of the inlet. For columns with a coated inlet this explains why peak distortion due to band broadening in space by a certain sample volume is pronounced in one case and hardly observable in another. Glass or fused silica capillaries silylated with diphenyltetramethyldisilazane were found to give optimal retention gaps. They combine thorough and thermostable deactivation with good wettability and low retention power. On the other hand it is very easy to deactivate fused silica capillaries with Carbowax. The resulting retention gaps are suitable for a wide range of applications and are particularly attractive for the analysis of dirty samples which require frequent replacement of the inlet. 相似文献
37.
Nek M. Shaikh S. Hafeez M.A. Baig 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007,62(12):1311-1320
We report the measurement of the zinc and cadmium plasma parameters produced by the fundamental, second, and third harmonics of the neodymium-doped yttrium aluminium garnet laser. The excitation temperature has been determined from the Boltzmann plot method, whereas the electron number density is estimated from the Stark broadened profile of several spectral lines. The temporal evolution of the plasma has also been investigated. Besides, we present experimental relative transition probabilities of the Zn (4s5s 3S1 → 4s4p 3P0,1,2) and Cd (5s6s 3S1 → 5s5p 3P0,1,2) triplets and compare our data with that listed in the National Institute of Standards and Technology database. The experiments have been performed in air but also in He, Ne and Ar atmosphere to study the effects of ambient gas environment on the emission intensity of the atomic and ionic lines and on the plasma parameters. 相似文献
38.
It is difficult to quantify NH4+ by ion chromatography in the presence of high concentrations of Na+ due to peak overlap. The Dionex IonPac CS15 column, which contains phosphonate, carboxylate, and 18-crown-6 functional groups, was originally developed to overcome this problem. We have found that the addition of 18-crown-6 to the eluent promotes improved peak resolution between Na+ and NH4+ even at concentrations as high as 60,000 to 1 using this column. Its use also improves the separation of alkali and alkaline earth metal and amine cations. Mobile phase 18-crown-6 increased the retention times of CH3NH3+, NH4+, and K+, and decreased the retention time of Sr2+. The retention times of Li+, Na+, Mg2+, Ca2+, (CH3)2NH2+, and (CH3)3NH+ were not affected. This method makes possible the direct analysis of ammonia from nitrogenase, the enzyme responsible for biological nitrogen fixation. The resolution of the NH4+ peak from the Na+ and Mg2+ peaks improved from zero resolution to values of 6.19 and 5.65, respectively. This technique considerably reduces the analysis time of NH4+ in the presence of high concentrations of Mg2+ and Na+ over traditional indophenol measurements. 相似文献
39.
Anomalous energy loss distributions of l48Gd alpha particles have been observed in heavily implanted thin aluminium films. It is surmised that thin film micro-wrinkling is responsible for the observed effect and that the novel technique of energy loss spectral analysis (ELSA) should be useful in studies of the topography of such films. 相似文献
40.
Luis G. MacDowell Jorge Benet Nebil A. Katcho Jose M.G. Palanco 《Advances in colloid and interface science》2014
In this paper we review simulation and experimental studies of thermal capillary wave fluctuations as an ideal means for probing the underlying disjoining pressure and surface tensions, and more generally, fine details of the Interfacial Hamiltonian Model. We discuss recent simulation results that reveal a film-height-dependent surface tension not accounted for in the classical Interfacial Hamiltonian Model. We show how this observation may be explained bottom-up from sound principles of statistical thermodynamics and discuss some of its implications. 相似文献