Ammonia dissociation spectrum

Although the ammonia PICI spectrum of TATP is dominated by the m/z 240 [TATP + NH4] ion, attempts to perform CID studies of the ion trap-isolated ion failed to produce a significant yield of product ions. Calculated interaction energies between TATP and the ammonium cation were reported to be less than the peroxide bond dissociation energy [30].The ammonium ion that would presumably be formed by ejection from... 

The ammonia dimer dissociation spectrum was found to consist of two bands... 

The pretreatment temperature is an important factor that influences the acidic/ basic properties of solids. For Brpnsted sites, the differential heat is the difference between the enthalpy of dissociation of the acidic hydroxyl and the enthalpy of protonation of the probe molecule. For Lewis sites, the differential heat of adsorption represents the energy associated with the transfer of electron density toward an electron-deficient, coordinatively unsaturated site, and probably an energy term related to the relaxation of the strained surface [147,182]. Increasing the pretreatment temperature modifies the surface acidity of the solids. The influence of the pretreatment temperature, between 300 and 800°C, on the surface acidity of a transition alumina has been studied by ammonia adsorption microcalorimetry [62]. The number and strength of the strong sites, which should be mainly Lewis sites, have been found to increase when the temperature increases. This behavior can be explained by the fact that the Lewis sites are not completely free and that their electron pair attracting capacity can be partially modified by different OH group environments. The different pretreatment temperatures used affected the whole spectrum of adsorption heats... 

Fragmentation of peptides can also be observed with FTICR instruments. Infrared multiple photon dissociation (IRMPD) and electron capture dissociation (ECD) have been introduced as two alternative dissociation methods to the low-energy CID method. The IRMPD method produces many fragments that make the spectrum very complex and difficult to interpret. Some of the fragment types observed with IRMPD are b and y type ions or these ions that have lost ammonia or water. However, most of them are not these types of fragment ions. 

The collision-induced dissociation (CID) spectrum of the m/z 94 ions, recorded at 20 eV kinetic energy, features only three peaks associated with the losses of H (m/z 93, 12%), NH3 (m/z 77, 86%) and [NH3+C2H2] (m/z 51, 1.5%) see Figure 13a. The very efficient ammonia loss confirms that we are dealing with the IV-protonated... 

This same full-scan and SRM approach used for ACs is also done for amino acids. Basic amino acids such as citrulline and arginine are characterized by loss of 102 Da and ammonia or other basic amino side chain. Selective reaction monitoring (SRM) is used rather than full scan and is based on NL of 119 for citrulline (102 -I-17, where 17 is ammonia) and NL of 161 for arginine (102 -i- 59, where 59 is the amino side chain). These SRMs are often grouped together in the visual spectrum as shown in Figure 13.12. Note that citrulline can also be acquired in an NL 102 scan since source-induced dissociate may cause the ammonia to be lost and hence detection of m/z 215 (MH+ minus 17) versus m/z 232. Details of this fragmentation are described elsewhere. 

The microkinetics analysis, as a useful and powerful tool to interpret, harmonize and consolidate the study of catal3dic phenomena, can describe various results obtained at wide experimental conditions. For ammonia synthesis reaction discussed in this section, the microkinetic models are evaluated from the experimental data such as the sticking coefficient of dissociated nitrogen adsorption, the spectrum of programmed-temperature desorption of adsorbed nitrogen as well as the kinetics of ammonia synthesis at industrial conditions and at laboratory conditions are far from equilibrium. 

ZnO is considered to be amphoteric and both basicity and acidity have been experimentally shown. The IR spectrum of NH3 adsorbed indicated the presence of Lewis acidity. The basicity on the basis of the IR study on the adsorption of Brensted acids (hydrocarbons, alcohols, and ammonia) has been reported. Those acids with Ka s greater than 36 did not dissociate. Ka of propene is 35 and that for ammonia 36. Therefore, it was concluded that the surface of ZnO posseses a basicity compar-ble with the conjugate base anions of Bronsted acids with pKa 36. The dissociative adsorption of Bronsted acids with Ka less than 19 was later reconfirmed. ... 

The dissociation is facile because the bond energy for the dissociation is only 15 kcal/mol for acetic acid and 11 kcal/mol for ammonia. The net effect of the complete process [Eqs. 1.20 and 1.21] is equivalent to a proton transfer from the ionized basic site to the ionized acidic site. Thus the molecular weight of the protein was not changed, but the positive and negative groups were neutralized. Thus a clean mass spectrum of the protein is obtained without a mass change. 

As already discussed in Section 2.3 of Chapter 2, Norman et al. have demonstrated the use of O2 + for the detection of NH3 [53]. It is difficult to quantify atmospheric ammonia when using H3O+ as the reagent ion because significant quantities of NH4+ are believed to be formed by reaction with N2 diffusing into the ion source. However, use of O2 as the reagent ions means that non-dissociative charge transfer can be employed leading to an NH3 + ion, which will appear in a mass spectrum at miz 17 and is therefore free from any interference from NH4 +. 

Figure 2.1 Comparison of El (a) and Cl (b and c) mass spectra of methamphetamine (mol wt = 149 Da). The Cl gas was methane and ammonia in case of (b) and (c), respectively, resulting in different degrees of dissociation. While the El mass spectrum does not contain the molecular ion at m/z 149, Cl gave rise to the [M + H] ion at m/z 150 using both reagent gases.

The particular structural features of AICAR (Fig. 4.18, 2) that includes an aminoimidazole moiety as well as a ribofuranose residue are reflected in its mass spectrometric dissociation behavior as shown with its product ion mass spectrum (obtained after positive ESI and CID Fig. 4.19b). Numerous product ions originating from consecutive losses of water (-18 Da) and ammonia (-17 Da) were found at m/z 242,241,223,205, and 188, and most abundant fragment ions resulting from the aminoimidazole-carboxamide nucleus were observed at m/z 127 and 110. Assuming an initial protonation of the primary amino function, the neutral loss of the ribose residue (2-hydroxymethyl-2,3-dihydro-furan-3,4-diol, -132 Da) gives rise to the protonated 5-amino-imidazole-4-carboxamide m/z 127) that subsequently releases ammonia (-17 Da) to yield the cation of imidazole-4-carboxamide with m/z 110 (Scheme 4.11b). ... 

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