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Data processing<br />
Peak picking a … Data processing<br />
Peak picking and alignment were performed using the Profiling Solution software (version 1.0.76.0; Shimadzu). The profiling solution parameters were as follows: ion m/z tolerance, 20 mDa; ion RT tolerance, 0.1 min; ion intensity threshold, 2e4; detect isomer valley, 20%; allow some ion without isotope peak, ON. The data matrix containing ~480 ions consisting of negatively detected ions was exported from the profiling solution software and normalized relative to the intensity of the [M+HCO2]− ion of the internal standard (1,2-didecanoyl-glycero-3-phosphocholine). Annotation was based on the theoretical m/z values of each lipid species and the retention time of identified compounds with the same polar head.<br />
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Statistics for the analysis of lipidomic data<br />
Normalized LC-MS data were pareto-scaled and subjected to OPLS-DA using SIMCA-P (version 11.0.0.0; Umetrics). Tukey' s test and Welch' s t-test were performed using their respective functions (TukeyHSD and t-test) in the statistical software R version 2.14.0 ( http://www.r-project.org/). HCL and jackknife testing were performed on MultiExperiment Viewer (MeV) version 4.8 ( http://www.tm4.org/mev/). For HCL, Pearson’s correlations were used to analyse the distance metric. Average linkage clustering was selected for the linkage method. The data set used for HCL is available as ‘Supplementary Data Set.xls’. Metadata also can be found in the same file. tadata also can be found in the same file.
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