Total current traces from

Figure 2. Total ion current traces from positive and negative ion LC/MS analyses of dithiopyr 1.

Figure 11. Total ion current trace from negative ion LC/MS analysis of the urinary metabolites of the...

Figure 5.27 Selective detection of lactolated peptides from a tryptic digest of / -lacto-globulins by LC-electrospray-MS-MS, showing (a) the total-ion-cnrrent trace in full-scan mode, and (b) the total-ion-current trace in neutral-loss-scanning mode. Figure from Selective detection of lactolated peptides in hydrolysates by liquid chromatography/ electrospray tandem mass spectrometry , by Molle, D., Morgan, F., BouhaUab, S. and Leonil, J., in Analytical Biochemistry, Volume 259, 152-161, Copyright 1998, Elsevier Science (USA), reproduced with permission from the publisher.

Figure 5.49 (a) Total-ion-current trace, and (b) the reconstructed ion chromatogram of mjz 510.2 0.5 (monooxygenated metabolites) from LC-MS analysis of human microsomal incubation of Glyburide. Reprinted with permission from Zhang, H., Henion, J., Yang, Y. and Spooner, N., Anal. Chem., 72, 3342-3348 (2000). Copyright (2000) American Chemical Society. 

A reconstructed ion chromatogram is a plot showing the variation in intensity of an ion of a particular m/z ratio as a function of analysis time, while the total-ion-current trace shows the variation in the intensity of all ions being produced as a function of analysis time. Simplistically, the TIC will show an increase as a compound elutes from an HPLC column and is ionized. If an ion with a particular m/z value is found to be diagnostic of a compound or series of compounds of interest, then an RIC of this m/z will show where its intensity increases and, therefore, where a compound of interest may have eluted. The mass spectrum at this point can then be examined for further confirmation that it is of significance. 

Figure 2.2 shows the total ion current trace and a number of appropriate mass chromatograms obtained from the pyrolysis gas chromatography-mass spectrometry analysis of the polluted soil sample. The upper trace represents a part of the total ion current magnified eight times. The peak numbers correspond with the numbers mentioned in Table 2.1 and refer to the identified compounds. The identification was based on manual comparison of mass spectra and relative gas chromatographic retention times with literature data [34, 35] and with data of standards available. In some cases unknown compounds were tentatively identified on the basis of a priori interpretation of their mass spectra (labelled tentative in Table 2.1). 

Fig. 11.4 shows the total ion current trace and some mass chromatograms obtained by flash evaporation pyrolysis gas chromatography-mass spectrometric analysis of the polluted sediment sample. All compounds present in this complex mixture were not listed. A selection was made to exemplify several aspects of the screening approach. The peak number correspond with the numbers in Table 11.1. Identifications were based on the same criteria as mentioned above. Although several components were shown to be real pyrolysis products, all the compounds are present as such in the sample and resulted from simple thermal extraction from the wire. This was shown in separate analyses using ferromagnetic wires with a Curie temperature of 358°C. 

Fig. 2.7.2. (—)-LC-ESI-MS chromatograms of a standard APG solution, (a) Total ion current trace fromm/2 200 to 600. (b)XIC of Cg-, C10-, and Ci2-monoglucoside, and (c) XIC of Cg-, C10-, and Ci2-diglucoside. Peak numbering as in Table 2.7.1 indices a and b denote different stereoisomeric forms. (Separation on a RP-Cg column with a water/acetonitrile gradient) (Reprinted from [1],...

The APCI-RP-C 1 s - h - i I S ( / ) separation of this mixture consisted of the anionic nonylphenol derivatives besides synthetic by-products to the total ion current traces and selected mass traces as presented in Fig. 2.11.23. By-products from synthesis could be confirmed as... 

What is a reconstructed ion chromatogram (RIC) and how does it allow a specific compound to be located in the total-ion current (TIC) trace from an LC-MS analysis ... 

Fig. 12. Total ion current trace of the Curie-point pyrolysis gaschromatography mass spectrometry run of fossil sheath tubes isolated from the Solar Lake cyanobacterial mat sediments (Boon, 1984) 521...

These herbicides contain nitrogen and respond to both FID and AFID. However, the analysis of these compounds is complicated by their thermal instability. For example, the total ion current trace obtained from the GC-MS ofamethanolic solution of monolinuron shows four peaks (Fig. 9). The formation of these peaks is illustrated in Fig. 10. This thermal decomposition appears to be general for the substituted ureas and reaction of substituted phenyl isocyanates with higher alcohols also occurs. As certain substituted alkyl phenylcarbamates are used as pesticides in their own right, inert solvents such as ethyl acetate or hexane should always be used for injection. The mass spectra of the thermal... 

A total ion current trace obtained from the GC-MS of terbacil methylated with diazomethane is shown in Fig. 11. From this it can be seen that derivatisation by this method leads to a mixture of products. It is for this reason that the analytical scheme incorporates an initial gas chromatographic step prior to methylation. 

These data for successive scans are then stored for subsequent manipulation. The reconstructed total ion current trace, equivalent to that obtained from a flame ionisation detector in gas chromatography, shows the variation of total ion current with time and allows spectra of interest to be identified. A typical example is shown in Fig. 6A. The background may be subtracted to give clean spectra, and their identification may be attempted using libraries of standard spectra. If a composite spectrum is obtained from two unresolved peaks, complex subtraction routines may be used to obtain a pure spectrum of each of the components. These may be separately submitted for library searching. The spectra may then be plotted or obtained as a mass versus intensity listing. 

Fig. 6. Reconstructed total ion current trace (A) and a single ion chromatogram from mjz 91 (B) for a typical GC-MS run.

Fig. 5.26. Total ion current (TIC) traces from clustered data tiles and corresponding mass spectra. (Reprinted with permission from 142. )...

Sensitivity of Electron Capture Ionization. We have found that negative ion LC/MS provides substantial increases in sensitivity as compared with positive ion LC/MS during analysis of fluorinated pyridines such as dithiopyr 1. An example of such sensitivity enhancement is shown in Figure 2. The top panel illustrates the total ion current trace obtained from injection of increasing amounts of dithiopyr in the positive ion mode with discharge ionization. 

In making measurements by sampled-current voltammetry, one would obtain traces like those in Figure 5.6.1. The diffusion current for the first wave can be subtracted from the total current of the composite wave to obtain the current attributable to O alone. That is. 

Because LC-MS can have some difficulty in distinguishing between isomers, some instruments have UV detection too (before the MS). This allows compounds of the same mass to be separated, identified and quantified. In LC-UV-MS, the UV detector is nondestructive so the sample passes into the MS unchanged. Connecting detectors in series in this way allows the analyst two ways of seeing the molecules that are eluting. The UV detector sees any chromophores and delivers a UV chromatogram. The MS detects any ions and delivers a total ion current trace. These two traces can be superimposed and it can be immediately seen which compounds respond best to which detector. Sometimes, a molecule is only seen by one detector and not the other. As well as the traces obtained above, further useful information can be obtained from the two detectors in series. The MS can yield a mass spectrum for any compound of interest and the UV detector (if it is a PDA) a UV spectrum for any compound of interest. This is illustrated in Figure 3.44. 

Fig. 15.7 One of the first published ion chro- of quaternary ammonium compounds. Repro matography application interfaced by ESI with duced with permission from [473] American MS. ESI-IC-MS(+) total ion current trace (TIC) Chemical Society 1990. and selected mass traces of an industrial blend...

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