Window factor

Quinn et al. followed the reaction of a nucleoside with trityl chloride in pyridine at 50 °C on the laboratory scale. This reaction is the first step of an industrially significant process. The UV-vis spectra were analyzed with chemometric analysis where automatic window factor analysis (WFA) yielded better results than PLS. A reactive intermediate, a solvated carbocation, was identified that had not been found with HPLC (quenching upon aliquot dilution) or NIR, respectively. Small, sudden process upsets could be detected. 

J.-H. Jiang, Y. Ozaki, M. Kleimann and H.W. Siesler, Resolution of two-way data from on-line Fourier-transform Raman spectroscopic monitoring of the anionic dispersion polymerization of styrene and 1,3-butadiene by parallel vector analysis (PVA) and window factor analysis (WFA), Chemom. Intell. Lab. Syst., 70, 83-92... 

SORS spatially offset Raman system WEA window factor analysis... 

Frequently, however, the lack of specificity in an analytical technique can be compensated for with sophisticated data processing, as described in the chemometrics chapter of this text (Chapter 8). Quinn and associates provide a demonstration of this approach, using fiber-optic UV-vis spectroscopy in combination with chemometrics to provide realtime determination of reactant and product concentrations.23 Automatic window factor analysis was used to evaluate the spectra. This technique was able to detect evidence of a reactive intermediate that was not discernable by off-line HPLC, and control charting of residuals was shown to be diagnostic of process upsets. Similarly, fiber-optic NIR was demonstrated by some of the same authors to predict reaction endpoint with suitable precision using a single PLS factor.24... 

Window factor analysis (WFA) was described by Malinowski and is likely the most representative and widely used noniterative resolution method [34, 35], WFA recovers the concentration profiles of all components in the data set one at a time. To do so, WFA uses the information in the complete original data set and in the subspace where the component to be resolved is absent, i.e., all rows outside of the concentration window. The original data set is projected into the subspace spanned by where the component of interest is absent, thus producing a vector that represents the spectral variation of the component of interest that is uncorrelated to all other components. This specific spectral information, combined appropriately with the original data set, yields the concentration profile of the related component. To ensure the specificity of this spectral information, all other components in the data set should be present outside of the concentration window of the component to be resolved. This means, in practice, that component peaks with embedded peak profiles under them cannot be adequately resolved. 

Malinowski, E.R., Window factor analysis theoretical derivation and application to flow injection analysis data, J. Chemom., 6, 29-40, 1992. 

Table 6.7 Fixed sized window factor analysis applied to the data in Table 6.1 using a three point window.

The regions of elution for each component can be similarly defined as for EFA above. There are numerous variations on fixed sized window factor analysis, such as changing the window size across die chromatogram, and the results can change... 

Problem 6.2 Evolutionary and Window Factor Analysis in the Detection of an Embedded Peak... 

Fixed-size moving-window-evolving factor analysis (FSMW-EFA). This technique, also called window factor analysis (WFA), is based on a window of a predefined number of rows or spectra, typically from three to five, which... 

FIGURE 9.9. Evaluation of the peak purity of the tryptamine system, (a) Experimental data set (b) determination of the number of components by SVD and (c) study of impurities by window factor analysis. 

F.C. Sanchez, S.C. Rutan, M.D. Gil Garcia and D.L. Massart, Resolution of Multicomponent Overlapped Peaks by the Orthogonal Projection Approach, Evolving Factor Analysis and Window Factor Analysis, Chemom. Intell. Labs. Syst. 36 (1997), 153-164. 

E.R. Malinowski, Window Factor Analysis Theoretical Derivation and Appliea-tion to Flow Injection Analysis Data, J. Chemom. 6 (1992), 29-40. 

X.G. Shao and W.S. Cai, Resolution of Multicomponent Chromatograms by Window Factor Analysis with Wavelet Transform Preprocessing, J. Chemom. 12... 

A.K. Elbergali, R.G. Brereton and A. Rahmani, Influence of the Method of Calculation of Noise Thresholds on Wavelength Selection in Window Factor Analysis of Diode Array High-Performance Liquid Chromatography, Analyst (London) 121 (1996), 585-590. 

Brereton, R. G. and Elbergali, A. K. (1994) Use of double windowing, variable selection, variable ranking and resolvability indices in window factor analysis. Journal of Chemometrics, 8, 423-37. 

Chromatograms by Window Factor Analysis with Wavelet Transform Preprocessing. 

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