Mass chromatogram

The three-dimensional data field of GC-MS analyses in the full-scan mode does not only allow the determination of the total ion intensity at a point in the scan. To show individual analytes selectively, the intensities of selected ions (masses) from the TIC are shown and plotted as an intensity/time trace (EIC or XIC extracted ion chromatogram, also mass chromatogram). A meaningful assessment of S/N ratios of certain substance peaks can only be carried out using mass chromatograms of substance-specific ions (fragment/molecular ions). 

The evaluation of these mass chromatograms allows the exact determination of the detection Hmit using the S/N ratio of the substance-specific ion produced by a compound. With the SIM/MID mode, this ion would be detected exclusively, but a complete mass spectrum for confirmation would not be available. In the case of complex chromatograms of real samples, mass chromatograms offer the key to the isolation of co-eluting components so that they can be integrated perfectly and quantified. 

In the analysis of lemons for pesticide residues, a co-elution situation was discovered by data acquisition in the full scan mode of the ion trap detector and was evaluated using mass chromatograms. 

Molecular weight 298 Purity HUXi Fit laaci Rfit laail Cas 13593-03-8 

Molecular weight 358 Purity BWil FltESiy Rfit (b) LiBR(NB) (purity, mass range 95-366, weight range 100-500) 

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Once the peaks have been collected and stored, the computer can be asked to work on the data to produce a mass spectrum and print it out, or it can be asked to carry out other operations such as library searching, producing a mass chromatogram, and making an accurate mass measurement on each peak. Many other examples of the use of computers to process mass data are presented in other chapters of this book. 

Once the mass spectral information has been acquired, various software programs can be employed to print out a complete or partial spectrum, a raw or normalized spectrum, a total ion current (TIC) chromatogram, a mass chromatogram, accurate mass data, and metastable or MS/MS spectra. 

Figure 5.37 Mass chromatograms of the (M + H) ions from four analytes, with each introduced from a separate HPLC column into an electrospray source. From de Biasi, V., Haskins, N., Organ, A., Bateman, R., Giles, K. and Jarvis, S., Rapid Commun. Mass Spectrom., 13, 1165-1168, Copyright 1999. John Wiley Sons Limited. Reproduced with permission.

Fig. 9A,B GC-MS analysis of the pheromone extract of Anadevidia peponis (Noctuidae, 1 FE) treated with DMDS A TIC B mass chromatograms [141]. The mass chromatograms, which are multiplied by indicated factors, monitor the M+ of DMDS adducts derived from C10 to C16 monoenyl acetates (m/z 292,320,348, and 376) and some diagnostic fragment ions (m/z 89,117,145,173,175,203,231, and 259) to determine their double-bond position. Peaks I-VI indicate the DMDS adducts of the following components in the pheromone gland Z5-10 OAc (I),Z5-12 OAc (II),Z7-12 OAc (III), ll-12 OAc (IV),Z9-14 OAc (V), and Zll-16 OAc (VI)...

Figure 8.12 Mass chromatogram of m/z 453 of the organic residues extracted from a bowl recovered from Amarna. O, methyl moronate Q, methyl oleanonate U, methyl masticadie nonate W, methyl isomasticadienonate 1 4, unidentified compounds with a base peak at m/z 453. Reproduced from B. Stern, C. Heron, L. Corr, M. Serpico, j. Bourriau, Archaeometry, 45, 457 469. Copyright 2003, with permission from Blackwell...

Figure 4.4 depicts a LC/MS assay utilizing fast chromatography.8 The throughput of the assay, which used a 4 x 20 mm C4 column, was limited only by the cycle time of the autosampler. Heart-cut column switching was not required because of the little background interference above m/e 300 in a thermospray mass chromatogram. 

FIGURE 4.3 Total LC/MS ion chromatogram of an Abbott compound, the analog internal standard, its metabolites and impurities. Depending on the need to assay the polar metabolite, 23 to 50% of the mass chromatogram will not show useful information (arrows). 

Using this technology, two or more complete mass chromatograms could be generated at the same time although the dwell time for each data point and the sampling rate (number of data points in time) are reduced as shown in Table 4.1. MUX and other multiple sprayer approaches require new interfaces and MS software. The multiple sprayer approach is only available in limited models of LC/MS instruments. 

FIGURE 7.9 (A) Upper traces show HPLC/MS/MS mass chromatograms for a set of six test compounds (total HPLC assay time ca. 3 min). (B) Lower traces show UPLC/MS/MS mass chromatograms for the same set of six test compounds (total UPLC assay time ca. 1 min). (Source Adapted from Yu, K. et al., Rapid Com-mun. Mass Spectrom., 2006, 20, 544. With permission of John Wiley Sons.)... 

FIGURE 7.12 Metabolite profile of bile sample obtained from a dog dosed with 20 mg/kg of a 14C-labeled test compound (A) total mass chromatogram of unprocessed LC/MS data (B) total mass chromatogram after mass defect filter processing (C) radioactivity chromatogram. (Source Adapted from Zhang, H.D. and Ray, K J. Mass Spectrom., 2003, 38, 1110. With permission of John Wiley Sons.)... 

FIGURE 11.9 Representative mass chromatogram of everolimus (6.77 pg/L) and SDZ RAD 223-756 as internal standard (25 ug/l.) in a blood sample from a renal transplant patient. (Source From Korecka, M. et al., TherDrug Monit. 28, 487, 2006. With permission.)... 

Figure 5.3. GC-MS analysis of organic pollutants in a sample of natural water, (a) Total ion current chromatogram (b) reconstructed ion current chromatogram (c) mass chromatogram based on the ion m/z 149 current.

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