Two-dimensional correlation analysis

Two-Dimensional correlation analysis to study Bronsted acid sites in zeolites... 

Two-dimensional data analysis [160, 161] is a very powerful technique that examines correlated changes in spectra with changes in any other measurement of sample perturbation. The elegance of the method demonstrated in earlier studies has been extensively augmented by finer details on application and numerous examples. The primary advantage of two-dimensional correlation analysis lies in the extension of data examination space to a second domain. Subtle changes that may not be easily discernable in spectra and even weak spectral effects may be easily enhanced and understood in the context of molecular spectra [162]. 

Further reported examples include electrocatalytic processes and their intermediates [313, 314]. Formate could be identified as an active intermediate of methanol electrooxidation at a polycrystalline platinum electrode [315]. Water molecules coadsorbed during methanol adsorption on platinum were identified as those species that react subsequently with COad that was formed as a result of methanol chemisorption [316]. The high sensitivity of SEIRAS allows mapping of two-dimensional spectra (for selected examples, see [285]). Finally, two-dimensional correlation analysis of electrochemical reactions becomes possible [317]. 

Y. Wang, R. Tsenkova, M. Amari, F. Terada, T. Hayashi, A. Abe, Y. Ozaki Potential of Two-Dimensional Correlation Spectroscopy in Analysis of NIR Spectra of Biological Fluids. I. Two-Dimensional Correlation Analysis of Protein and Fat Concentration-Dependent Spectral Variations of Milk", Analusis Magazine, 1998 26, M64-M69... 

Phase-locked electronics are used to record the dynamic IR spectral change in-phase and out of phase with the applied mechanical field. The method provides insight to the response to the external stress on the molecular and submolecular scale. Rheooptical FTIR spectroscopy is one of the few techniques providing data on the crystallisation, orientation and conformational changes of a polymer during mechanical treatment (83). Two dimensional correlation analysis is utilised to enhance the information derived from the vibrational spectroscopic data. 

Infrared, near-infrared, and Raman spectroscopy were used to study high density, linear low density (LLDPE), and low density polyethylene. Overlapping spectral bands were separated using the second derivative, principal component analysis, and two-dimensional correlation analysis. A model was developed, using partial least squares regression, to calculate the density of LLDPE. 1 ref. 

Results of the above studies are presented and discussed in relation to the potential of three powerful techniques, i.e. two-dimensional correlation analysis, the calculation of the second derivatives and calculation of regression coefficients in chemometrics, in examining the rather complex near-lR spectra. 22 refs. 

Some new developments of two-dimensional spectroscopy are discussed. As a specific example, two-dimensional correlation analysis of a polymer laminate film using several different spectroscopic techniques is presented. The versatility of this technique was developed using depth-profiling photoacoustic spectroscopy, mid-and near-IR dynamic rheooptical developments, and spectroscopic imaging microscopy. Spatial and temporal variations of near-IR spectra are effectively analysed by the two-dimensional correlation technique. Step-scanning FTIR spectrometers provide an opportunity to obtain desired spectral information often difficult to obtain by the conventional rapid-scanning technique. 12 refs. 

Two-dimensional FTIR spectroscopy was used to study the N-H stretching and amide I/amide II region of melt-crystallised nylon 11 thin films on Teflon substrates. The samples were dynamic mechanically oscillated at room temp, at a frequency of 11 Hz. A two-dimensional correlation analysis on the dynamic spectra indicated that the N-H stretching region split into two peaks. Analysis... 

Dynamic mechanical analysis coupled with polarised step-scan FTIR transmission and two-dimensional correlation analysis was used to monitor the submolecular orientational responses of the components of a semicrystalline 50/50 blend of LDPE with perdeuterated HDPE to a small amplitude uniaxial 23.47 Hz sinusoidal mechanical strain. Perdeuteration of the HDPE component allowed the distinction of its response from that of the LDPE in the blend samples. Experiments were carried out at room temp. Analysis of the data indicated that the crystalline parts of the two components reorient at different rates, with the functional groups of the high density portion reorienting faster, in general, than those of the LDPE in response to the mechanical strain. 29 refs. USA... 

INTERPRETATION OF DYNAMIC IR SPECTRA TWO-DIMENSIONAL CORRELATION ANALYSIS... 

X-ray absorption near-edge structure X-ray photoelectron spectroscopy two dimensional correlation analysis of IR dynamic spectra... 

S. Sasic, Two-dimensional correlation analysis of nuclear magnetic resonance meta-bonomics data, Appl. Spectrosc. 62 (2008) 840. 

I. Noda, Double two-dimensional correlation analysis—2D correlation of 2D spectra, J. Mol. Stmct. 974 (2010) 108. 

B. Czarnick-Matusewicz, K. Murayama, R. Tsenkova, Y. Ozaki. Comparison of two-dimensional correlation analysis and chemometrics in near infrared spectroscopy protein and fat concentration-dependent spectral changes. In Near Infrared Spectroscopy Proceedings of 9th International Corference, A. M. C. Davies, R. Giangiacomo, eds. NIR Publications, Chichester, UK, 2000, p. 17-23. 

The first measurements of this type were reported by Palmer et al. [18], who noted the similarity of the experimental setup for dynamic polymer rheo-optical measurements and liquid-crystal electroreorientation. However, because the changes in the polarized spectmm on switching the electric field can be very large, the measurement of liquid-crystal electroreoiientation tends to be much easier than the DIRLD measurements described in Section 21.2. Two-dimensional correlation analysis is frequently used to aid in interpreting the results. 

The real part (vj, V2) of the complex cross correlation function is referred to as the synchronous spectrum, while the imaginary part 9 (vi, V2) is called the asynchronous spectrum. The practical significance of the correlation spectra related to applications in physical science and the step-by-step derivation of the above equation central to the two-dimensional correlation analysis are provided in this appendix. 

The cross correlation function given in Equation (F6) may be further modified to a form better suited for the two-dimensional correlation analysis with the help of the Wiener-Khintchine theorem [5]. This theorem conveniently relates the cross correlation function with the corresponding Fourier transforms. In the first step, the expression for the dynamic spectrum y(v2, t -I- t) in Equation (F6) is rewritten in terms of the inverse of Fourier transform of y(v2, s )-... 

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