Selected ion plot

We wanted to monitor the chemical composition distribution across the MWD. This can be accomplished by summing all the selected-ion plots for the MMA BAq, MMA BAi, MMA BA2, and MMA BAs, respectively. We used a 2-Da window to obtain the selected-ion plots. For example, the selected-ion plot for the MMA2BA trimer (351 Da eq... 

Figure 6. Selected-ion plots o/MMAn, MMA BAi, MMAnBA2, and MMA BAs oligomers.

FIG. 2. Data retrieval following repetitive scanning. Selected ion plot (top figure) for ions characteristic of the major urinary metabolite of Dianabol, 6g-hydroxy-Dianabol. Complete spectrum (lower figure) of scan 320 in which all selected ions are peaking. 

However, the employment of "maximising ion" criteria (6) resolved this dilemma since summed ion intensity plots separated the 19-nor--pregnanetriol from an endogenous steroid 5-pregnene-33,16a,20a--triol, the source of the m/e 157 and 144 peaks. A selected ion plot of m/e 245 from the maximising ion data showed a similar increase in resolution from selected ion plots from unprocessed data (Fig. 3). Metabolites of Nilevar and Orabolin have not yet... 

Selected ion plots (top figure) to differentiate endogenous androsterone and etiocholanolone (m/e 362 and 272) from major Durabolin metabolites 19-nor-androsterone and 19 nor-etiocholanolone (m/e 348 and 258). Lower figure shows ion plots from undrugged control sample. 

In addition to this major advantage of comprehensive data collection, repetitive scanning techniques form the basis of other approaches to the analysis of multicomponent mixtures. Most common of these is the selected ion plot in which the block of mass spectral data from a repetitive scan run is inspected for particular ions. These are then represented as a plot of ion intensity versus scan number (see Figs. 5.8 and 5.9). In these figures, ions characteristic of spectra of 4-hydroxyphenylacetic acid and pentonic acids are plotted, and their positions in the chromatogram can be clearly seen. As the pentonic acid isomers are eluted under the peaks of hippuric and citric acids, their detection in composite spectra is not always definitive. 

Selected ion plots may also be of value to detect a small amount of a compound in the presence of large amounts of other compounds. In favourable instances, ions characteristic of the compound which appear insignificant on a relative intensity basis against compound background ions, can show up clearly. 

To recognise ion suppression reactions, the AE blend was mixed together either (Fig. 2.5.13(a) and (b)) with the cationic quaternary ammonium surfactant, (c, d) the alkylamido betaine compound, or (e, f) the non-ionic FADA, respectively. Then the homologues of the pure blends and the constituents of the mixtures were quantified as presented in Fig. 2.5.13. Ionisation of their methanolic solutions was performed by APCI(+) in FIA-MS mode. The concentrations of the surfactants in the mixtures were identical with the surfactant concentrations of the blends in the methanolic solutions. Repeated injections of the pure AE blend (A 0-4.0 min), the selected compounds in the form of pure blends (B 4.0—8.8 min) and their mixtures (C 8.8— 14.0 min) were ionised and compounds were recorded in MID mode. For recognition and documentation of interferences, the results obtained were plotted as selected mass traces of AE blend (A b, d, f) and as selected mass traces of surfactant blends (B a, c, e). The comparison of signal heights (B vs. C and A vs. C) provides the information if a suppression or promotion has taken place and the areas under the signals allow semi-quantitative estimations of these effects. In this way the ionisation efficiencies for the pure blends and for the mixture of blends that had been determined by selected ion mass trace analysis as reproduced in Fig. 2.5.13, could be compared and estimated quite easily. 

Figure 2.2. The change with changing aromatic ring substituent X in the azide (az) ion selectivities (feaz/ s)obsd ( ) determined by analysis of the products of the reactions of ring-substituted 1-phenylethyl derivatives (X-l-Y) and ring-substituted cumyl derivatives (X-2-Y) in 50/50 (v/v) water/trifluoroethanol at 25 The selectivities are plotted...

Figure 2.5. Nucleophile selectivities determined from product analysis for the reactions of ring-suhstituted 1-phenylethyl derivatives (X-l-Y) with azide ion, acetate ion and methanol in 50 50 (v/v) water/trifluoroethanol. The selectivities are plotted against the appropriate Hammett substituent constant or a. Leaving group Y ( ) ring-suhstituted benzoates ( ) chloride (T) dimethyl sulfide (A) tosylate.

Figure 11. Photoion photoelectron coincidence studies of charge-transfer reactions of state-selected ions. Cross sections for nitric oxide symmetric charge-transfer reaction are plotted as function of reactant-ion kinetic energy and reactant-ion vibrational state (o = 0,1,2,3,4,5). Solid lines are linear least-squares fits to experimental data (not shown).86c...

Mass spectra recorded using LC/MS software may be displayed individually, signal averaged, and background subtracted. Furthermore, these data may be used to plot computer-reconstructed selected ion or total ion chromatograms. 

Another technique used for the computation of metal ion selectivities, where plots of strain energy vs. metal ligand equilibrium distance r0 are produced and interpreted, is discussed in Chapter 8[°21. 

In recent years the application of electrospray ionization (ESI) mass spectrometry, quadrupole time-of-flight (QqTOF) mass spectrometry, and Fourier transform ion cyclotron resonance (FT-ICR) are used for further structural characterization of DOM (Kujawinski et al., 2002 Kim et al., 2003 Stenson et al., 2003 Koch et al., 2005 Tremblay et al., 2007 Reemtsma et al., 2008). MS/MS capabilities provide the screening for selected ions, and FT-ICR allows exact molecular formula determination for selected peaks. In addition, SEC can be coupled to ESI and FTICR-MS to study different DOM fractions. Homologous series of structures can be revealed, and many pairs of peaks differ by the exact masses of -H2, -O, or -CH2. Several thousand molecular formulas in the mass range of up to more than 600 Da can be identified and reproduced in element ratio plots (O/C versus H/C plots). Limitations of ESI used by SEC-MS are shown by These and Reemtsma (2003). 

Figure 19 Standard addition calibration curves. Equal volumes of solvent containing varying amounts of standard are added (spiked) into the sample. The samples are analyzed and the analyzer response (e.g., area under the TIC or selected ion chromatogram) is plotted against the amount of standard added. The analyte concentration is estimated by extrapolating a linear least-squares regression toy = 0 (a). An alternative approach is to plot the difference between the spiked samples and the unspiked sample. The same calibration curve now passes through the origin and the sample analyte concentration can now be determined by interpolation with improved confidence limits164 (b).

The linearity of these plots, coupled with the similarity of slopes between univalent and divalent ion lines for each form of Nafion, suggests that for both forms a constant increment in entropy occurs per released water molecule. The slopes of these lines are 0.90 and 0.94 kJ mol 1 at 25°C for alkali ion and alkaline earth ion plots, normal form and 0.53 and 0.40 kJ mol 1 for the expanded form of Nafion. These values can account for the magnitudes of the selectivity coefficients, even though they are less than 10% of the entropy increase for water release from... 

Figure 7.3 plots the ratio of crystal radius versus charge for selected ions. Oxyanions—sulfate, selenate, phosphate, arsenate, borate, molybdate, carbonate, and silicate—are represented by their central cations S6+, Se6+, P5+, As5+, B3+, Mo4+, C4+, and Si4+. The ions fall into three behavioral groups. Ions of high ionic potential, the alkali and alkaline earth cations and the halide anions, large univalent and divalent ions, are highly water soluble, easily weatherable, and leach readily from soils to the sea over geologic time. 

Figure 4a. Selected ion summation plots for (A) naphthalene and (B) dimethylnaphthalenes...

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