Ion current traces

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. 

Total-ion-current trace A plot of the total number of ions reaching the mass spectrometry detector as a function of analysis time. 

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). 

Because no pretreatment of the samples was carried out, the peaks present in the total ion current trace reflect components generated by pyrolysis of primary compounds ( real pyrolysis products ) and components that are present as such in the sample and simply evaporate ( free products ). If desired these two types of products may be differentiated using wires with a Curie temperature of 358°C [36], It was demonstrated in separate analyses (not shown here) that most compounds were not generated by pyrolysis but were present as such in the sample and thermally extracted . Compounds 1-8 and 10-17, 27, 37, 38, 54 and 65 were only present in pyrolysis gas... 

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. 2.5.13. Ion current traces of APCI-FIA-MS(+) examinations of compound interferences performed in multiple ion detection mode applied for quantification of pure AE blend (A AE b,d,f recorded between 0 and 4.0 min), pure quat (B a), betaine (B c) and FADA (B e) blend (cf. B Selected compounds a,c,d recorded between 4.0 and 8.5 min). In mixtures of AE with quat, betaine or FADA, respectively, all constituents were determined by MID (cf. C Mixture AE/quat (a,b), AE/betaine (c,d), and AE/FADA (e,f) (recorded between 8.5 and 14.0 min, respectively). Ions recorded in MID mode for quantification AE (all ions starting at m/z 306 + A 44 and ending at 966), quat m/z 214 and 220, betaine m/z 184, 212, 240, 268, 285, 296, 313, 324 and 341, FADA m/z 232, 260,...

Fig. 2.5.14. Total ion current trace of APCI-FIA-MS(+) examinations for interferences induced by inorganic compounds (K+ and Na+) injected during the ionisation of an continuously infused AE/NH4Ac solution. 

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... 

Sulfosuccinates, as presented with their general structural formula in Fig. 2.11.33, are applied as surfactants for personal hygiene because of their hypoallergenic features. The sodium salt of the sulfosuccinate blend with the formula ROOC-CH-(SC>3 )-CH2-COOR Na+ (R = CsH-iy) was examined by APCI-FIA-MS in the positive and negative modes. The addition of an excess of ammonium acetate under FIA-APCI-MS(+) conditions resulted in [M — NH4]+ ions with mlz 440 while [M — H] ions with mlz 421, however, were observed in the negative APCI-FIA-MS mode (Fig. 2.11.34(a)). Only one type of ion could be observed in this industrial blend by FIA-MS. This purity could also be confirmed by APCI-LC-MS(-), as shown in the total ion current trace (cf. Fig. 2.11.34(b)), which is presented in combination with the averaged mass spectrum under the signal in the inset of Fig. 2.11.34(b) [22],... 

From the separation of a mixture of both compounds applying RP-Cis and ESI-MS(—), it was recognisable from mass trace analysis that the Ci2 derivative eluted first as shown in Fig. 2.11.36(c) and (d) [64]. The signals in the reconstructed ion current trace (e) contained the same ions at mtz 745 or 639 and at m/z 372 or 319 as also observed under ESI-FIA-MS(—) conditions. 

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.

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. 

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

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