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|Title:||Pure component reconstructions using entropy minimizations and variance-weighted piecewise-continuous spectral regions. Application to the unstable experimental system Co2(CO)8/Co4(CO)12|
Exploratory chemometric studies
Pure component spectra
Singular value decompositions
|Source:||Pan, Y., Susithra, L., Garland, M. (2000). Pure component reconstructions using entropy minimizations and variance-weighted piecewise-continuous spectral regions. Application to the unstable experimental system Co2(CO)8/Co4(CO)12. Journal of Chemometrics 14 (2) : 63-77. ScholarBank@NUS Repository. https://doi.org/10.1002/(SICI)1099-128X(200003/04)14:2<63::AID-CEM577>3.0.CO;2-9|
|Abstract:||The organometallic complex Co2(CO)8 is an air-, light-, heat- and moisture-sensitive species and rapidly decomposes in n-hexane solutions to give Co4(CO)12. Owing to the instability of Co2(CO)8, calibration is extremely difficult. Moreover, the published literature measurements of the mid-infrared spectrum of Co2(CO)8 are inconsistent. To solve this problem, a chemometric approach involving singular value decompositions and entropy minimizations was used. First, n-hexane solutions of mixtures of Co2(CO)8 and Co4(CO)12 were prepared and measured in the mid-infrared on the interval 1700-2200 cm-1. After spectral subtractions of n-hexane and background gases, two absorbance matrices were constructed, namely the unweighted matrix A(8 x 2501) and the piecewise-continuous variance-weighted matrix A(8x2501)/*. The piecewise-continuous variance-weighted matrix possesses a discontinuity at 1925 cm-1, between the region of strong terminal carbonyl vibrations and the region of weak bridging carbonyl vibrations, where both regions have strongly overlapping characteristics. The significant right singular vectors V(2x2501)/(T) and V(2x2501/(T*) were then subjected to both second-derivative and fourth-derivative entropy minimizations. In addition, two numerical modifications were implemented, namely full-spectrum optimizations and half-spectrum optimizations. It was found that extremely good spectral estimates for Co2(CO)8 and Co4(CO)12 were obtained from (i) the global solutions for both the unweighted and variance-weighted second-derivative entropy minimizations when using the half-spectrum minimizations and (ii) the local solutions for both the unweighted and variance-weighted fourth-derivative entropy minimizations when using both the half-spectrum and full-spectrum minimizations. These results suggest that (a) half-spectrum optimizations and second-derivative entropy measures are potentially very useful for particular types of real strongly overlapping spectra, (b) the failure of the fourth-derivative entropy measures to produce the correct estimates is probably associated with the sensitivity to experimental noise and (c) although the variance-weighted approach did not help in the present case, variance-weighted analyses still hold potential for spectral analyses involving both strong and weak absorbance characteristics. Copyright (C) 2000 John Wiley and Sons, Ltd.|
|Source Title:||Journal of Chemometrics|
|Appears in Collections:||Staff Publications|
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