Comparison of the internal energy deposition of direct analysis in real time and electrospray ionization time-of-flight mass spectrometry

Abstract

The internal energy (E int ) distributions of a series of p-substituted benzylpyridinium ions generated by both direct analysis in real time (DART) and electrospray ionization (ESI) were compared using the "survival yield" method. DART mean E int values at gas flow rates of 2, 4, and 6 L min Ϫ1 , and at set temperatures of 175, 250, and 325°C were in the 1.92-2.21 eV range. ESI mean E int at identical temperatures in aqueous and 50% methanol solutions ranged between 1.71 and 1.96 eV, and 1.53 and 1.63 eV, respectively. Although the results indicated that ESI is a "softer" ionization technique than DART, there was overlap between the two techniques for the particular time-of-flight mass spectrometer used. As a whole, there was an increase in E int with increasing reactive and drying gas temperatures for DART and ESI, respectively, indicating thermal ion activation. Three dimensional computational fluid dynamic simulations in combination with direct temperature measurements within the DART ionization region revealed complex inversely coupled fluid-thermal phenomena affecting ion E int values during atmospheric transport. Primarily, that DART gas temperature in the ionization region was appreciably less than the set gas temperature of DART due to the set gas flow rates. There was no evidence of E int deposition pathways from metastable-stimulated desorption, but fragmentation induced by high-energy helium metastables was observed at the highest gas flow rates and temperatures. (J Am Soc Mass Spectrom 2010, 21, 855-863)

Sensitivity “Hot Spots” in the Direct Analysis in Real Time Mass Spectrometry of Nerve Agent Simulants

“…As a whole, the number of stable water cluster isomers increases exponentially with n [24]. The higher abundance of specific clusters has been observed previously with DART [20], but that study showed relative higher levels of water clusters n=3, 6, 9, and 12 for various temperatures (175, 250, and 325°C) and flow rates (2, 4, and 6 Lmin ). Although there are no significant differences in binding energies [25] and bond dissociation energies [26] for water clusters in the range 9≤n≤17, the atmospheric pressure interface in the instrument used in this study (GIST-capillarydual ion funnel) is much different than that in previous work (cone/skimmer orifice) [20].…”

“…The higher abundance of specific clusters has been observed previously with DART [20], but that study showed relative higher levels of water clusters n=3, 6, 9, and 12 for various temperatures (175, 250, and 325°C) and flow rates (2, 4, and 6 Lmin ). Although there are no significant differences in binding energies [25] and bond dissociation energies [26] for water clusters in the range 9≤n≤17, the atmospheric pressure interface in the instrument used in this study (GIST-capillarydual ion funnel) is much different than that in previous work (cone/skimmer orifice) [20]. Therefore, we believe that the observed differences in water cluster species are an effect caused more by the ion transfer optics design and reduced pressure region architecture than the by preferential formation or reactivity of particular species.…”

“…As a whole, the suppression observed at 200°C was greater at all positions than at 300 and 400°C, indicating that proton exchange is more favorable for higher PA analytes at lower temperatures. This may be due to the lower thermodynamic stability of smaller protonated water clusters at lower temperatures, a phenomenon that has been observed with both DART [20] and APCI [23]. At 200°C, ion suppression for position B1 ranged from 6 to 26× in the tested concentration range (50-500 μM), and was similar for positions B2 and B3, ranging from 7 to 19× (Fig.…”

“…Previous observations have shown there is a steep temperature gradient along the line connecting the DART gas nozzle to the mass spectrometer inlet [16,20]. However, given that sample surface areas may extend beyond the center-line of the ionization region, the temperature of the relative sensitivities in the entire ionization region were now mapped ( Fig.…”

Surface analysis of lipids by mass spectrometry: More than just imaging

“…For example, TAGs have been detected from olive oil desorbed from a glass rod, with a ten-fold increase in signal observed by doping ammonia into the gas stream to facilitate [M+NH 4 ] + ion formation [241]. However, desorption/ionization of TAGs resulted in significant fragmentation, a phenomenon not uncommon in DART and one that generally increases with gas temperature [245,246]. This leads to formation of DAG-like ions with greater abundance than ions arising from intact TAG molecules, thereby reducing sensitivity and making…”