Two-Dimensional Correlation Optimized Warping Algorithm for Aligning GC×GC−MS Data

Abstract

A two-dimensional (2-D) correlation optimized warping (COW) algorithm has been developed to align 2-D gas chromatography coupled with time-of-flight mass spectrometry (GC x GC/TOF-MS) data. By partitioning raw chromatographic profiles and warping the grid points simultaneously along the first and second dimensions on the basis of applying a one-dimensional COW algorithm to characteristic vectors, nongrid points can be interpolatively warped. This 2-D algorithm was directly applied to total ion counts (TIC) chromatographic profiles of homogeneous chemical samples, i.e., samples including mostly identical compounds. For heterogeneous chemical samples, the 2-D algorithm is first applied to certain selected ion counts chromatographic profiles, and the resultant warping parameters are then used to warp the corresponding TIC chromatographic profiles. The developed 2-D COW algorithm can also be applied to align other 2-D separation images, e.g., LC x LC data, LC x GC data, GC x GC data, LC x CE data, and CE x CE data.

Pixel-Level Data Analysis Methods for Comprehensive Two-Dimensional Chromatography

“…While all of these alignment algorithm approaches have merit, for the chemometric analysis of pixel-level data, the most commonly applied preprocessing approaches implemented are the latter. The locally and globally optimized alignment algorithms can handle severe and dynamic shifting in comprehensive 2D chromatography applications, because they are robust, powerful, and essentially automated in every regard after the initial parameter selections have been made by the analyst [24,50,51,[54][55][56][57][58][59].…”

Application of Chemometrics to the Interpretation of Analytical Separations Data

“…The use of multiple intervals permits the alignment of separations data where shifts of different magnitudes and directions occur. These alignment algorithms have been used successfully for both one-dimensional data (de la Mata-Espinosa, 2011a; Laursen, 2010) and two-dimensional data, with some modifications (Zhang, 2008). It is important to note that the shifting of chromatograms using coshift or icoshift does not lead to distortions of peak shape, and consequently does not introduce errors into quantitative results.…”

Comprehensive two dimensional gas chromatography review

“…Then, depending on the type of analysis to be performed (generalized rank annihilation method, PARAFAC) and the complexity of the samples, peak alignment may be necessary for sets of chromatograms. Zhang et al [137] addressed the problem of peak aligment for chemometric methods. Using samples of human serum with amino acids, fatty acids and organic acids they used correlation optimized warping to align chromatograms.…”