Alignment for Comprehensive Two-Dimensional Gas Chromatography
with Dual Secondary Columns and Detectors
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Abstract
In each sample run, comprehensive
two-dimensional gas chromatography
with dual secondary columns and detectors (GC × 2GC) provides
complementary information in two chromatograms generated by its two
detectors. For example, a flame ionization detector (FID) produces
data that is especially effective for quantification and a mass spectrometer
(MS) produces data that is especially useful for chemical-structure
elucidation and compound identification. The greater information capacity
of two detectors is most useful for difficult analyses, such as metabolomics,
but using the joint information offered by the two complex two-dimensional
chromatograms requires data fusion. In the case that the second columns
are equivalent but flow conditions vary (e.g., related to the operative
pressure of their different detectors), data fusion can be accomplished
by aligning the chromatographic data and/or chromatographic features
such as peaks and retention-time windows. Chromatographic alignment
requires a mapping from the retention times of one chromatogram to
the retention times of the other chromatogram. This paper considers
general issues and experimental performance for global two-dimensional
mapping functions to align pairs of GC × 2GC chromatograms. Experimental
results for GC × 2GC with FID and MS for metabolomic analyses
of human urine samples suggest that low-degree polynomial mapping
functions out-perform affine transformation (as measured by root-mean-square
residuals for matched peaks) and achieve performance near a lower-bound
benchmark of inherent variability. Third-degree polynomials slightly
out-performed second-degree polynomials in these results, but second-degree
polynomials performed nearly as well and may be preferred for parametric
and computational simplicity as well as robustness