Heat capacity of associated systems. Experimental data and application of a two-state model to pure liquids and mixtures

The predictions from a recently reported (J. Chem. Phys. 2004, 120, 6648) two-state association model (TSAM) have been tested against experimental data. The temperature, T, and pressure, p, dependence of the isobaric heat capacity, C(p), for three pure alcohols and the temperature dependence at atmospheric pressure of the excess heat capacity, C(p)(E), for four alcohol + ester mixtures have been measured. The branched alcohols were 3-pentanol, 3-methyl-3-pentanol, and 3-ethyl-3-pentanol, and the mixtures were 1-butanol and 3-methyl-3-pentanol mixed with propyl acetate and with butyl formate. These data, together with literature data for alcohol + n-alkane and alcohol + toluene mixtures, have been analyzed using the TSAM. The model, originally formulated for the C(p) of pure liquids, has been extended here to account for the C(p)(E) of mixtures. To evaluate its performance, quantum mechanical ab initio calculations for the H-bond energy, which is one of the model parameters, were performed. The effect of pressure on C(p) for pure liquids was elucidated, and the variety of C(p)(E)(T) behaviors was rationalized. Furthermore, from the C(p) data at various pressures, the behavior of the volume temperature derivative, (deltaV/deltaT)(p), was inferred, with the existence of a (deltaV/deltaT)(p) versus T maximum for pure associated liquids such as the branched alcohols being predicted. It is concluded that the TSAM captures the essential elements determining the behavior of the heat capacity for pure liquids and mixtures, providing insight into the macroscopic manifestation of the association phenomena occurring at the molecular level.     

Simultaneous simplification of loading and core matrices in N-way PCA: application to chemometric data arrays

In the Tucker3 model of N-way principal components analysis (NPCA), a so-called core matrix describes the possible interactions between components from different modes. For an easy interpretation of solutions, it is necessary to have as few interactions as possible (in conventional PCA of data tables, such interactions can always be avoided). This goal may be realized by various approaches of core matrix transformations. At the same time, it is desirable to have simple component (or loading) matrices. Usually, the simplicity of the core conflicts to a certain degree with the simplicity of the components. The paper demonstrates how the conditional optimization of both goals can be used to find a compromise. For the purpose of illustration, the procedure is first applied to a small three-way data array from heavy metal analysis of tissues in different samples of game. Later, a data array of bigger size from a three-way interlaboratory study is considered. Received: 21 November 1997 / Revised: 11 February 1998 / Accepted: 15 February 1998     

Simultaneous simplification of loading and core matrices in N-way PCA: application to chemometric data arrays

In the Tucker3 model of N-way principal components analysis (NPCA), a so-called core matrix describes the possible interactions between components from different modes. For an easy interpretation of solutions, it is necessary to have as few interactions as possible (in conventional PCA of data tables, such interactions can always be avoided). This goal may be realized by various approaches of core matrix transformations. At the same time, it is desirable to have simple component (or loading) matrices. Usually, the simplicity of the core conflicts to a certain degree with the simplicity of the components. The paper demonstrates how the conditional optimization of both goals can be used to find a compromise. For the purpose of illustration, the procedure is first applied to a small three-way data array from heavy metal analysis of tissues in different samples of game. Later, a data array of bigger size from a three-way interlaboratory study is considered. Received: 21 November 1997 / Revised: 11 February 1998 / Accepted: 15 February 1998     

Real-time two-dimensional wavelet compression and its application to real-time modeling of ion mobility data

Real-time data analysis is important in many applications. However, many chemometric algorithms have difficulty processing data in real-time. A novel real-time two-dimensional wavelet compression (WC²) has been developed to compress data as it is acquired from analytical instrumentation. The WC algorithm was enhanced so that data with an arbitrary number of points were compressed, and truncation or padding to a dyadic number was avoided. After compression, the noise level is reduced while useful chemical information is retained. A modified simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) algorithm was applied to the wavelet-compressed data and the model was transformed back to the original representation while leaving the data compressed. The reduced size of the wavelet-compressed data furnished a faster implementation of SIMPLISMA that facilitates real-time acquisition.

This real-time WC²-SIMPLISMA algorithm was applied to the rapid identification of explosives by ion mobility spectrometry (IMS). SIMPLISMA resolved concentration profiles and component spectra were displayed simultaneously while the data was acquired from an ion mobility spectrometer with a LabVIEW virtual instrument (VI).     

The destruction-free analysis of polymers by fourier transform infrared photoacoustic and fourier transform Raman spectroscopy: A comparison

With the introduction of rapid–scanning Fourier transform infrared (FTIR) and recently Raman (FT–Raman) spectroscopy, vibrational spectroscopy has been launched into a new era of applications in polymer chemistry and physics. Thus, the increase in sensitivity provided by multiple scanning has led to the breakthrough of new, destruction–free sampling techniques, such as photoacoustic and Raman spectroscopy. This paper provides a comparison between data produced by FTIR photoacoustic and FT–Raman analysis of a range of polymers, and structural information available from both techniques is discussed.     

Bicyclic 1,2,3-triazolium ionic liquids: synthesis, characterization, and application to rutaecarpine synthesis

Starting with commercial reagents, bicyclic 1,2,3-triazolium ionic liquids [b-3C-tr][NTf(2)] (1) and [b-4C-tr][NTf(2)] (2) were synthesized in four steps with high overall isolated yields of 68% and 76%, respectively. Since the C-5 hydrogen is acidic, under basic condition ionic liquids 1 and 2 were readily methylated with methyl iodide to afford chemically stable ionic liquids 7 and 8 at room temperature (88% and 82%, respectively). Ionic liquid 1 was used as the ionic solvent to demonstrate its usefulness for the synthesis of rutaecarpine, a natural product.     

Thermal restraint on PEG-EG mixtures by FTIR investigations and wavelet cross-correlation analysis

The aim of the present work is to investigate the thermal response of PolyEthylene Glycol 1000 (PEG1000) and of its mixtures with the monomer Ethylene Glycol (EG). On purpose Attenuated Total Reflectance Infra-Red (ATR-IR) spectra were collected, in the spectral range spanning from 400 cm⁻¹ to 4000 cm⁻¹, on PEG1000 and on its mixtures with EG, as a function of concentration and temperature, through positive thermal scans, i.e. by increasing temperature. It will be shown that ATR-IR technique reveals a powerful tool for the characterization of the thermal response in polymeric systems. The registered spectra have been analyzed both on the whole investigated spectral range, as well as, separately, on the restricted intramolecular OH stretching vibrational contribution region. In the first case the displacement of the spectral features from the spectrum at the lowest temperature, taken as reference spectrum, shows a lower dependence for the mixture. As far as the intramolecular OH vibrational contribution is concerned, besides a conventional analysis in terms of band components, three different data analysis procedures have been applied, i.e. the characterization of the temperature dependence of the intramolecular OH stretching center frequency, of the spectral distance and of the wavelet cross correlation coefficient. The three applied data analysis approaches indicates that the addition of a small amount of pure EG to PEG1000 significantly influences the OH vibrational properties of the PEG1000 polymeric matrix. The three different methods furnish a unique coherent interpretative picture which supports the validity of the applied approaches. Furthermore, the analyses show the presence of a higher thermal restraint for the PEG + EG mixture which confirms that, within the three-dimensional networks of hydrogen bonded EG-PEG1000 mixtures, a key role is played by EG in determining an increase of the hydrogen bond network density.     

Orthogonal signal correction, wavelet analysis, and multivariate calibration of complicated process fluorescence data

In this paper, multivariate calibration of complicated process fluorescence data is presented. Two data sets related to the production of white sugar are investigated. The first data set comprises 106 observations and 571 spectral variables, and the second data set 268 observations and 3997 spectral variables. In both applications, a single response, ash content, is modelled and predicted as a function of the spectral variables. Both data sets contain certain features making multivariate calibration efforts non-trivial. The objective is to show how principal component analysis (PCA) and partial least squares (PLS) regression can be used to overview the data sets and to establish predictively sound regression models. It is shown how a recently developed technique for signal filtering, orthogonal signal correction (OSC), can be applied in multivariate calibration to enhance predictive power. In addition, signal compression is tested on the larger data set using wavelet analysis. It is demonstrated that a compression down to 4% of the original matrix size — in the variable direction — is possible without loss of predictive power. It is concluded that the combination of OSC for pre-processing and wavelet analysis for compression of spectral data is promising for future use.     

Suspended trapping gas chromatography I fourier transform mass spectrometry for analysis of complex organic mixtures

The superior sensitivity, dynamic range, and mass measurement accuracy of suspended trapping pulse sequences for gas chromatography combined with Fourier transform mass spectrometry (GC/FTMS) separations of complex organic mixtures is demonstrated. By combining intense ionization conditions with a suspended trapping event prior to detection the working range of the trapped ion cell is increased by 10³. Improved detection limits are shown for the GC/FTMS separation of a peppermint oil, with the suspended trapping total ion chromatogram yielding 28 peaks, compared with 15 with a conventional trapping pulse sequence. A fivefold to fifteenfold improvement in signal-to-noise for suspended trapping measurements is also demonstrated with comparison spectra from separations of an unleaded gasoline sample. Suspended trapping spectra show little mass discrimination when an external ion reservoir is used, and chromatographic peak heights differ from conventional spectra by less than 30% if the initial ion population is within the space charge limit of the cell. Finally, average wide band mass measurement errors for components differing in concentration by several orders of magnitude are improved by a factor of 6 to 20 with suspended trapping compared with conventional trapping. For example, average errors of 8.7 ppm are obtained for a suspended trapping GC/FTMS separation of peppermint oil from a single calibration table in which the analysis is performed in the absence of calibrant.     

Capillary electrophoresis mass spectrometry and its application to the analysis of biological mixtures

Capillary electrophoresis (CE) mass spectrometry (MS), with its ability to separate compounds present in extremely small volume samples rapidly, with high separation efficiency, and with compound identification capability based on molecular weight, is an extremely valuable analytical technique for the analysis of complex biological mixtures. The highest sensitivities and separation efficiencies are usually achieved by using narrow capillaries (5-50 micro m i.d.) and by using sheathless CE-to-MS interfaces. The difficulties in CE-to-MS interfacing and the limited loadability of these narrow columns, however, have prevented CE-MS from becoming a widely used analytical technique. To remedy these limitations, several CE-MS interfacing techniques have recently been introduced. While electrospray ionization is the most commonly used ionization technique for interfacing CE-to-MS, matrix assisted laser desorption ionization has also been used, using both on-line and off-line techniques. Moreover, the high concentration detection limit of CE has been addressed by development of several sample concentration and sample focusing methods. In addition, a wide variety of techniques such as capillary zone electrophoresis, capillary isoelectric focusing, and on-column transient isotachophoresis have now been interfaced to MS. These advances have resulted in a rapid increase in the use of CE-MS in the analysis of complex biological mixtures. CE-MS has now been successfully applied to the analysis of a wide variety of compounds including amino acids, protein digests, protein mixtures, single cells, oligonucleotides, and various small molecules relevant to the pharmaceutical industry.     

Swarm intelligence based wavelet coefficient feature selection for mass spectral classification: An application to proteomics data

This paper introduces the ant colony algorithm, a novel swarm intelligence based optimization method, to select appropriate wavelet coefficients from mass spectral data as a new feature selection method for ovarian cancer diagnostics. By determining the proper parameters for the ant colony algorithm (ACA) based searching algorithm, we perform the feature searching process for 100 times with the number of selected features fixed at 5. The results of this study show: (1) the classification accuracy based on the five selected wavelet coefficients can reach up to 100% for all the training, validating and independent testing sets; (2) the eight most popular selected wavelet coefficients of the 100 runs can provide 100% accuracy for the training set, 100% accuracy for the validating set, and 98.8% accuracy for the independent testing set, which suggests the robustness and accuracy of the proposed feature selection method; and (3) the mass spectral data corresponding to the eight popular wavelet coefficients can be located by reverse wavelet transformation and these located mass spectral data still maintain high classification accuracies (100% for the training set, 97.6% for the validating set, and 98.8% for the testing set) and also provide sufficient physical and medical meaning for future ovarian cancer mechanism studies. Furthermore, the corresponding mass spectral data (potential biomarkers) are in good agreement with other studies which have used the same sample set. Together these results suggest this feature extraction strategy will benefit the development of intelligent and real-time spectroscopy instrumentation based diagnosis and monitoring systems.     

Metal sols in ionic liquids: synthesis,properties, and application

This review contains the analysis of the state-of-the-art data on synthesis, structure, and practical application of metal sols in ionic liquids. Problems related to stabilization of metallic nanoparticles by the components of ionic liquids are analyzed in detail. Information on catalytic properties of metal sols in ionic liquids is generalized. Examples illustrating practical application of these systems in diverse areas of science and technology are presented.

     

Porous ionic liquids: synthesis and application

Solidification of fluidic ionic liquids into porous materials yields porous ionic networks that combine the unique characteristics of ionic liquids with the common features of polymers and porous materials. This minireview reports the most recent advances in the design of porous ionic liquids. A summary of the synthesis of ordered and disordered porous ionic liquid-based nanoparticles or membranes with or without templates is provided, together with the new concept of room temperature porous ionic liquids. As a versatile platform for functional materials, porous ionic liquids have shown widespread applications in catalysis, adsorption, sensing, actuation, etc. This new research direction towards ionic liquids chemistry is still in its early stages but has great potential.     

A new reverse wormlike micellar system: mixtures of bile salt and lecithin in organic liquids

We report a new route for forming reverse wormlike micelles (i.e., long, flexible micellar chains) in nonpolar organic liquids such as cyclohexane and n-decane. This route involves the addition of a bile salt (e.g., sodium deoxycholate) in trace amounts to solutions of the phospholipid lecithin. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique "facially amphiphilic" structure, can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than 5 orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.     

Fast, generic gradient high performance liquid chromatography coupled to fourier transform ion cyclotron resonance mass spectrometry for the accurate mass analysis of mixtures

Fast gradient high performance liquid chromatography (HPLC) has been combined with a commercially available Fourier transform ion cyclotron resonance (FTICR) mass spectrometer for the routine and high performance analysis of mixtures. With this combination we were able to separate and detect, under high mass accuracy conditions, a six-component drug mixture in less than 5 minutes. The fast gradients described are now possible due to the development of mechanically robust, ultra pure silica packing materials, which allow relatively high flow rates (ca. 1 mL/min for a 2 mm diameter column). For the six compounds present in the model mixture, relative mass errors of less than 1 ppm were obtained (based on an external calibration) providing sufficient mass accuracy to make unequivocal assignments of empirical formulae. Preliminary results of fast gradient HPLC/FTICR-MS/MS are also shown for the same six-component mixture. Copyright 2000 John Wiley & Sons, Ltd.     

Phase separation in mixtures of ionic liquids and water

The phase separation of ionic liquids (ILs) in water is studied by laser light scattering (LLS). For the ILs with longer alkyl chains, such as [C(8)mim]BF(4) and [C(6)mim]BF(4) (mim = methylimidazolium), macroscopic phase separation occurs in the mixture with water. LLS also reveals the coexistence of the mesoscopic phase, the size of which is in the order of 100-800 nm. In aqueous mixtures of ILs with shorter alkyl chains, such as [C(4)mim]BF(4), only the mesoscopic phase exists. The mesoscopic phase can be effectively removed by filtration through a 0.22 μm filter. However, it reforms with time and can be enhanced by lowering the temperature, thus indicating that it is controlled by thermodynamics. The degree of mesoscopic phase separation can be used to evaluate the miscibility of ILs with water. This study helps to optimize the applications of ILs in related fields, as well as the recycling of ILs in the presence of water.     

Boundary viscosity of polydimethylsiloxane liquids and their binary mixtures

A systematic study is made of the boundary viscosity of a number of polydimethylsiloxane liquids (PMS) of molecular weights ranging from 1,000 to 40,000 by the blow-off method, film thicknesses being measured by a modulation-polarimetric (elliposmetric) precedure. It is established experimentally that the viscosity of the liquids studied is not the same throughout the thickness of the boundary later.

PMS applied to glass and steel substrates retain their bulk viscosity values down to a layer thickness of ca. 150–200 Å, below which the viscosity increases slightly. On further decrease of the distance to 10–15 Å from the substrate, the viscosity becomes anomalously low, amounting to about 10–20 % of the bulk value. The existence of a layer of anomalously low viscosity may be attributed to orientation of the PMS molecules in the plane of the substrate, and hence, to the ease with which these oriented layers slip relative to one another.

When studying the boundary viscosity of binary mixtures of PMS of different molecular weights, boundary phases of elevated viscosity were found to exist at a distance of 15–30 Å from the substrate. This phenomenon may be attributed to a change in concentration of the mixture at the solid surface i.e., to an increase in content of the component with the higher molecular weight in the wall-adjacent layer.