A critical look at the definition of multidimensional separations

Multidimensional (MD) separations, especially comprehensive two-dimensional (2D) separations such as comprehensive 2D LC (LC × LC), and comprehensive 2D GC (GC × GC), are potentially powerful separation techniques. It is important to have a clear definition of MD techniques to better understand the scope and boundaries of the subject. Widely accepted definitions of MD Separations have their roots in the definition proposed by Giddings. Giddings also added several comments that clarified the scope of his definition. However, some researchers extend Giddings’ definitions beyond their intended scope. Doing so disqualifies such comprehensive 2D techniques as LC × LC, GC × GC and 2D TLC from being considered as 2D techniques. In other instances, extended treatment of Giddings’ definition is used as a basis to justify design-parameters of comprehensive 2D separations despite the fact that these parameters lead to sub-optimal implementations. We believe that the shortcomings in the definition and its popular interpretations are serious enough to warrant attention, especially by those interested in designing optimal instrumentation for MD separations like comprehensive 2D GC. After discussion of the weaknesses in the currently used definitions, we propose to define n-dimensional analysis as one that generates n-dimensional displacement information. We believe that this definition captures the spirit of Giddings’ definition while avoiding the problems associated with its popular interpretations.     

Error estimation in peak‐shape analysis of XPS core‐level spectra using UNIFIT 2003: how significant are the results of peak fits?

An error analysis for numerically evaluating random uncertainties in x‐ray photoelectron spectroscopy has been implemented in version 2003 of the spectra treatment and analysis software UNIFIT in order to improve the understanding of the statistical basis and the reliability of the model parameters for photoelectron spectra. The theoretical basis as well as two approaches to obtain error limits of the fit parameters have been considered. Several test spectra have been analysed and discussed. A representative example has been chosen to demonstrate the relevance of the error estimation for practical surface analysis. Suggestions for the minimization of errors in the peak‐fitting procedures are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

Wavelength Flexibility in Photoinitiated Cationic Polymerization

The spectral sensitivity of onium salt photoinitiators in cationic polymerization can be tuned from the short wavelength region of the UV spectrum to wavelengths up to the visible region by using direct and indirect activation, respectively. Indirect activation is based on the electron transfer reactions between onium salts and free radical photoinitiators, appropriate sensitizers and compounds capable of forming charge transfer complexes. Bisacylphosphine oxides, dimanganese decacarbonyl in conjunction with alkyl halides and titanocene type photoinitiators such as Irgacure 784 were shown to be useful free radical promoters providing the possibility of performing cationic polymerization in the long wavelength and visible region. The synthetic routes to prepare block copolymers by using electron transfer photosensitization and free radical promoted cationic polymerization are also described.     

Wavelength effect on the photoinduced reaction of polymethylmethacrylate

Polymethylmethacrylate (PMMA) containing benzophenone (BP) was photo-irradiated with monochromatic radiation of wavelength 260–360 nm using the Okazaki Large Spec-trograph (OLS). On irradiation of PMMA films containing BP in air, the sensitized main-chain scission and photocrosslinking of PMMA took place simultaneously. These reactions are dependent on irradiation wavelength. The threshold wavelength for both reactions is found to be ca. 380 nm. The number of main-chain scission and amount of gel increased with the increase of BP concentration in PMMA. Photosensitized main-chain scission favors the irradiation of radiation at ca. 280 nm and photocrosslinking takes place efficiently with the exposure of 340 nm radiation. A possible mechanism for photosensitized reaction is proposed. © 1995 John Wiley & Sons, Inc.     

三波长分光光度法研究：Ⅲ.两测量波长法提高测定灵敏度

本实验利用两测量波长法提高三波长光光度法的灵敏度，选择合适的波长组合，消除两种共存组分的干扰，使△Ａ＝Ａλ１＋Ａλ２－ＫＡλ３只与待测组分的浓度有关，灵敏度一般均高于单波长法。以相对误差为选择波长组合的标准，编制了程序，用计算机选择合适的波长组合，验证结果令人满意。     

Studies on external peak broadening in open-tubular liquid chromatography systems using the exponentially modified Gaussian model

Summary To optimize performance in Open-Tubular Liquid Chromatography (OTLC) it is necessary to minimize external peak broadening. To see how to reduce the external broadening an insight into its origins is required. This can be obtained by careful evaluation of experimental results with peak deconvolution methods based on the exponentially modified Gaussian model and comparison with theoretical predictions. It is assumed that the column response is Gaussian and that the responses due to the external effects are exponential.For peak deconvolution the algorithm described by Yau was used. Simulations were carried out to check the performance of the algorithm in calculating the standard deviation and the time constant. The effects of the presence of more than one time constant and of the number of data points and their position were investigated. The limits within which reliable results can be obtained are reported.Experimental results were obtained with laser-induced fluorescence and mass spectrometric detection. It is shown that the Yau algorithm can be used to obtain physically realistic estimates of the contribution to peak distortion in the various system components. By suitable design external effects can be reduced to the order of 1 nl and in some cases even lower limits can be reached.Part of this paper was presented at the 3rd Workshop on LC/MS and MS/MS, October, 24–26, 1984 in Montreux, Switzerland.     

Birefringence control by hydrogen bonding on compatible polymer pair composed of hydrogenated ring‐opening polymer and modified polystyrene

A new polymer blend composed of a hydrogenated ring‐opening polymer (HROP) with an ester group and hydroxyl functionalized polystyrene (HFP) produced the excellent transparent materials which enabled a precise birefringence control in keeping with the other physical properties for optical film use. The blend with a composition from 0.28 to 0.35 for the HFP weight fraction showed an extraordinary wavelength dispersion, transmitting through a zero birefringence point at the critical fraction of 0.45, while each polymer showed an ordinary wavelength dispersion. The observed excellent transparency even above those of the glass transition temperature was attributed to a depressed phase separation that resulted from strong hydrogen bond between the ester and hydroxyl groups. An IR analysis of the film demonstrated a remarkable red‐shift in the carbonyl peak with an increase of the hydroxylated polystyrene content, indicating a strong hydrogen bond between those groups. This new polymer blend provides a useful design to achieve practical demands for film use, both optical and mechanical under the fabrication conditions using the melt extrusion technique. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3132–3143     

塔板理论对柱内和柱外浓度分布曲线的描述

使用Visual Basic和QBasic程序，分别在Excel和DOS上，在不做任何化简的情况下，对塔板理论描述的柱内和柱外组分浓度分布进行了研究。发现符合线性分配的样品组分在色谱柱内存在3种不同的浓度分布形态，在色谱柱外则都是拖尾峰形态。分析了不同分配比对柱内和柱外浓度分布曲线最高点和次高点的影响。     

Heat capacity calorimetry

Experimental heat capacity measurements of α-ZrW₂O₈, and zeolitic polymorphs of SiO₂, BEA and MFI, have been made from 0.6 to 400 K. Measurements on β-ZrMo₂O₈ have been made from 8 to 400 K. Analysis of the results yields evidence for very low frequency modes in all four materials. These modes are responsible for negative thermal expansion behavior in α-ZrW₂O₈ and β-ZrMo₂O₈. Negative thermal expansion has been observed in some pure SiO₂ zeolites, but no studies have been made to look for it in BEA and MFI. The appearance of low frequency modes in these two zeolites suggests that temperature dependent structural investigations would be worthwhile. These modes are lower in energy than the Boson peak in vitreous silica. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of Permeation of Helium through the Walls of Fused Silica Capillary GC Columns

Hold-up times and peak widths have been measured in long fused silica GC capillary columns at high temperature with helium as the carrier gas. The results lead to the conclusion that the helium permeates through the column walls. The conventional Poiseuille theory of carrier gas flow has been extended to include this phenomenon. The resulting “loss modified Poiseuille” model, which uses literature values for the permeability of fused silica to helium, has been used to simulate the observed behavior. Good agreement between simulation and experiment validates the model. Simulations have been used to explore the effect of column permeability on hold-up times, peak widths, and velocity profiles over a broad range of column geometries.