Abstract:Comparing fast atom bombardment and field desorption collisionally activated dissociation mass spectra of tetrabutyl ammonium salts it becomes evident that under fast atom bombardment conditions, besides desorption of intact salt cations, the ionization of intact salt molecules must be assumed. Alkyl ions formed under fast atom bombardment and not under field desorption collisionally activated dissociation conditions are ionization products of tetraalkyl ammonium salt molecules. Radical cations are produced by… Show more
“…Figure b shows the EI mass spectrum of TBAP, which shows ions at m / z 242 ((C 4 H 9 ) 4 N + ), 142 ((C 4 H 9 ) 2 N + CH 2 ), 100 ((C 4 H 9 )(CH 3 )N + CH 2 ), and 57 ((C 4 H 9 ) + ). The mass spectra in Figure are in agreement with the on-line library spectra and the literature. , When TPA and TBAP are present together in acetonitrile solution, ions from the ionization of both TPA and TBAP appear in the mass spectrum, as shown in Figure c. 4 EI mass spectra of TPA, TBAP, and TPA/TBAP obtained by PB/MS: (a) 1 mM TPA; (b) 0.01 M TBAP; (c) 1 mM TPA/0.01 M TBAP in acetonitrile.…”
Anodic oxidation of triphenylamine (TPA) in acetonitrile was investigated by electrochemistry (EC) combined online with mass spectrometry (MS) through a particle beam (PB) interface, EC/PB/MS. Electrooxidation of TPA generates a TPA*+ radical cation (m/z 245) which dimerizes to tetraphenylbenzidine (TPB, MW 488). TPB is readily oxidized to TPB*+ (m/z 488) and TPB2+ (m/z 244) at the oxidation potential of TPA. In EC/PB/MS, direct monitoring of the oxidation of TPB to TPB*+ radical cation as a function of the electrode potential was achieved via selective ion monitoring of the ion peak at m/z 488. By using the relative intensity ratio of ions at m/z 244 (TPB2+) to 245 (TPA*+), the formation of TPB2+ as a function of the electrode potential was also monitored. EC/PB/MS showed a maximum rate of formation of TPB*+ at +1.2 Vvs Pd, while TPB2+ is generated at a maximum rate at +1.6 V vs Pd. The effect of spectral interference from the electron impact ionization of TPA, on EC/PB/MS results, is also discussed. Finally, a significant signal enhancement is observed in the presence of tetrabutylammonium perchlorate (TBAP) and is reported for the first time. Compatibility of coupling of EC with MS via PB interface for EC/MS studies in nonaqueous solvents is demonstrated. The observation of significant signal enhancement in the presence of TBAP may facilitate other applications of LC/MS.
“…Figure b shows the EI mass spectrum of TBAP, which shows ions at m / z 242 ((C 4 H 9 ) 4 N + ), 142 ((C 4 H 9 ) 2 N + CH 2 ), 100 ((C 4 H 9 )(CH 3 )N + CH 2 ), and 57 ((C 4 H 9 ) + ). The mass spectra in Figure are in agreement with the on-line library spectra and the literature. , When TPA and TBAP are present together in acetonitrile solution, ions from the ionization of both TPA and TBAP appear in the mass spectrum, as shown in Figure c. 4 EI mass spectra of TPA, TBAP, and TPA/TBAP obtained by PB/MS: (a) 1 mM TPA; (b) 0.01 M TBAP; (c) 1 mM TPA/0.01 M TBAP in acetonitrile.…”
Anodic oxidation of triphenylamine (TPA) in acetonitrile was investigated by electrochemistry (EC) combined online with mass spectrometry (MS) through a particle beam (PB) interface, EC/PB/MS. Electrooxidation of TPA generates a TPA*+ radical cation (m/z 245) which dimerizes to tetraphenylbenzidine (TPB, MW 488). TPB is readily oxidized to TPB*+ (m/z 488) and TPB2+ (m/z 244) at the oxidation potential of TPA. In EC/PB/MS, direct monitoring of the oxidation of TPB to TPB*+ radical cation as a function of the electrode potential was achieved via selective ion monitoring of the ion peak at m/z 488. By using the relative intensity ratio of ions at m/z 244 (TPB2+) to 245 (TPA*+), the formation of TPB2+ as a function of the electrode potential was also monitored. EC/PB/MS showed a maximum rate of formation of TPB*+ at +1.2 Vvs Pd, while TPB2+ is generated at a maximum rate at +1.6 V vs Pd. The effect of spectral interference from the electron impact ionization of TPA, on EC/PB/MS results, is also discussed. Finally, a significant signal enhancement is observed in the presence of tetrabutylammonium perchlorate (TBAP) and is reported for the first time. Compatibility of coupling of EC with MS via PB interface for EC/MS studies in nonaqueous solvents is demonstrated. The observation of significant signal enhancement in the presence of TBAP may facilitate other applications of LC/MS.
“…We also recorded the unimolecular fragmentation reactions occurring in the drift region between the magnetic and electric sectors; the results obtained were in good agreement with the data reported in Tables 1 and 2. The fragmentation reaction resulting in nominal elimination of C7HI6 from (C4Hg),N+ has been proposed earlier (8)(9)(10) to involve sequential elimination of C4Hg' and C3H7', viz rather than direct elimination of C7H16 (reaction [3]). …”
Section: Methodsmentioning
confidence: 99%
“…In contrast to the protonated amines, tetraalkyl ammonium ions, R4N+, show very abundant elimination of alkanes in metastable ion fragmentation reactions and in both low energy and high energy CID studies (6)(7)(8)(9)(10)(11). The nominal alkanes eliminated correspond to R H and to (R' + [R -CH,]'), the latter either as an alkane or as two alkyl radicals.…”
,2205 (1994). ' The unimolecular metastable ion and low-energy collision-induced fragmentation reactions of alkyl ammonium ions R,,H,.,,Nf (tz = 2 to4, R = tz-C3H7 and n-C,H9) have been studied and breakdown graphs expressing the % fragment ion abundances as a function of the centre-of-mass collision energy have been established. The dialkyl and trialkyl ammonium ions fragment primarily by olefin ([R -HI) elimination or by formation of the alkyl ion Rf (with rearrangement to the more stable secondary structure). By contrast the tetraalkyl ammonium ions show both elimination of [R -HI and elimination of an alkane, which is C,H12 for the propyl compound C7H,6 for the butyl compound. The results are interpreted in terms of competition between heterolytic bond cleavage to form a [Rf---NH,.,,R,,.,] complex and homolytic bond cleavage to form a [R,,-,H,.,,Nf.---'R] complex. The former complex fragments either to form R+ or undergoes internal proton transfer to form R,,-,H,.,,NH+ + [R -HI, while the latter complex fragments by alkane elimination resulting from attack of R' on the a-CC bond of the alkyl group. For the propyl ammonium ions plausible potential energy profiles are established which show that the former complex is favoured for n = 2, 3 while the two complexes have similar energies for n = 4. [Traduit par la rCdaction]
“…15,16 Unimolecular dissociations of gaseous ammonium ions have been studied by CAD for four decades. 6,[17][18][19][20] Alkene elimination is seen at the lowest accessible collision energies. This presents an opportunity to explore stereochemistry of the Hofmann elimination without having to consider interactions between the base and the quaternized salt, which render syn and anti-transition states comparable in energy.…”
The Hofmann elimination of ammonium ions having a single positive charge is demonstrated to exhibit stereospecificity with regard to expulsion of neutral alkene. For the 3-hexyl series of threo and erythro 4-monodeuterated ions (3-hexylammonium ion; N,N,N-trimethyl- d-3-hexylammonium ion; N-ethyl-3-hexylammonium ion; N-methyl, N-ethyl-3-hexylammonium ion; N,N-dimethyl, N-ethyl-3-hexylammonium ion), the upper limit of the E:Z ratio of the expelled alkene (r) approaches 2 (the stereospecificity) with a deuterium isotope effect close to 2.0, although the effects of isotopic substitution diminish the E:Z ratio somewhat. Two fragmentations compete with that reaction: hydride shift (which gives the same products but with hydrogen scrambling) and loss of a neutral amine to give an alkyl cation. These competing reactions render our calculation approximate, but the results suggest a value not too far from the upper limit.
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