MS Data Analysis

Description Objects from the Class Slots Methods Note Author(s) References See Also

This class is similar to xcmsSet because it stores peaks from a number of individual files. However, xcmsFragments keeps Tandem MS and e.g. Ion Trap or Orbitrap MS$^n$ peaks, including the parent ion relationships.

Objects can be created with the xcmsFragments constructor and filled with peaks using the collect method.

peaks:: matrix with colmns peakID (MS1 parent in corresponding xcmsSet), MSnParentPeakID (parent peak within this xcmsFragments), msLevel (e.g. 2 for Tandem MS), rt (retention time in case of LC data), mz (fragment mass-to-charge), intensity (peak intensity extracted from the original xcmsSet), sample (the index of the rawData-file).
MS2spec:: This is a list of matrixes. Each matrix in the list is a single collected spectra from collect. The column ID's are mz, intensity, and full width half maximum(fwhm). The fwhm column is only relevant if the spectra came from profile data.
specinfo:: This is a matrix with reference data for the spectra in MS2spec. The column id's are preMZ, AccMZ, rtmin, rtmax, ref, CollisionEnergy. The preMZ is precursor mass from the MS1 scan. This mass is given by the XML file. With some instruments this mass is only given as nominal mass, therefore a AccMZ is given which is a weighted average mass from the MS1 scan of the collected spectra. The retention time is given by rtmin and rtmax. The ref column is a pointer to the MS2spec matrix spectra. The collisionEnergy column is the collision Energy for the spectra.

collect: signature(object = "xcmsFragments"): gets a xcmsSet-object, collects ms1-peaks from it and the msn-peaks from the corresponding xcmsRaw-files.
plotTree: signature(object = "xcmsFragments"): prints a (text based) pseudo-tree of the peaktable to display the dependencies of the peaks among each other.
show: signature(object = "xcmsFragments"): print a human-readable description of this object to the console.