Mass chromatograms current profile

True profile analysis requires scanning over the whole mass range for the acquisition of all data on excreted compounds. Quantitation has been more challenging on a quadrupole instrument because total ion current peaks are seldom a single component and extracted-ion chromatograms (EICs) when recovered from scanned data are of poor quality due to the lower sensitivity of scanning GC-MS. Thus, we developed profile analysis based on SIM of selected analytes but tried to ensure the components of every steroid class of interest were included. For ion traps the fundamental form of data collection (in non-MS/MS mode must be full -scans). Thus, the quantitative data produced are EICs obtained from scanned data. The EICs are of the same ions used for SIM in quadrupole instruments and the calibration external standards are the same. 

Figure 2.13—Detection by mass spectrometry. TIC chromatogram obtained with a mass spectrometer as a detection system. The instrument is capable of obtaining hundreds of spectra per minute. The above chromatogram corresponds to the total ion current at each instant of the elution profile. It is possible to identify each of the components using its mass spectrum. In many instances, compounds can be identified with the use of a library of mass spectra. (Chromatogram of a mixture of 71 volatile organic compounds (VOCs), reproduced by permission ofTekmarand Restek, USA.)...

The capillary HPLC separation from a selected protein spot provides a base-peak profile shown in Figure 6.2A. The base-peak profile is similar to a total ion current (TIC) profile, but it contains only the most abundant mass spectral peak in each scan. The chromatogram is simplified and the contributions from background ion abundances are eliminated, resulting in an enhanced signal-to-ion ratio for an improved visualization of data. The molecular mass for each component is labeled along with corresponding amino acid residues. This format provides a comprehensive approach for peak selection and peptide identification. 

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