Novel ionization reagent for the measurement of gas‐phase ammonia and amines using a stand‐alone atmospheric pressure gas chromatography (APGC) source

Abstract

Rationale:Contaminants present in ambient air or in sampling lines can interfere with the target analysis through overlapping peaks or causing a high background. This study presents a positive outcome from the unexpected presence of N-methyl-2-pyrrolidone, released from a PALL HEPA filter, in the analysis of atmospherically relevant gas-phase amines using chemical ionization mass spectrometry.Methods: Gas-phase measurements were performed using a triple quadrupole mass spectrometer equipped with a modified atmospheric pressure gas chromatography (APGC) source which allows sampling of the headspace above pure amine standards.Gas-phase N-methyl-2-pyrrolidone (NMP) emitted from a PALL HEPA filter located in the inlet stream served as the ionizing agent. Results:This study demonstrates that some alkylamines efficiently form a [NMP + amine+H] + cluster with NMP upon chemical ionization at atmospheric pressure. The extent of cluster formation depends largely on the proton affinity of the amine compared with that of NMP. Aromatic amines (aniline, pyridine) and diamines (putrescine) were shown not to form cluster ions with NMP. Conclusions:The use of NMP as an ionizing agent with stand-alone APGC provided high sensitivity for ammonia and the smaller amines. The main advantages, in addition to sensitivity, are direct sampling into the APGC source and avoiding uptake on sampling lines which can be a significant problem with ammonia and amines.

Size-Resolved Chemical Composition of Sub-20 nm Particles from Methanesulfonic Acid Reactions with Methylamine and Ammonia

“…The desorbed species were then ionized ). We previously showed 107 that NMP exhibits good sensitivity and selectivity for measuring NH 3 and amines via the formation of [M + NMP + H] + and [M + 2NMP + H] + ions (where M represents either MA or NH 3 ); this is its first application as an ionization reagent in TDCIMS. Note that the soft X-ray source illuminated the entire ionization volume of the ion source.…”

“…TDCIMS can be performed in both positive and negative ion modes: MSA was measured in the negative ion mode with (H 2 O) n O 2 – ( n = 0–2) as the reagent ion, while both NH 3 and MA were measured in the positive ion mode with either (H 2 O) n H 3 O + ( n = 0–2) alone or added N -methylpyrrolidone (NMP; C 5 H 9 NO; MW = 99 g mol –1 ). We previously showed that NMP exhibits good sensitivity and selectivity for measuring NH 3 and amines via the formation of [M + NMP + H] + and [M + 2NMP + H] + ions (where M represents either MA or NH 3 ); this is its first application as an ionization reagent in TDCIMS. Note that the soft X-ray source illuminated the entire ionization volume of the ion source.…”

Composition of Ultrafine Particles in Urban Beijing: Measurement Using a Thermal Desorption Chemical Ionization Mass Spectrometer

“…(NMP) n H + was used as the positive reagent ion, instead of the commonly used (H 2 O) n H + , to selectively detect nitrogen-containing base compounds. (NMP) n H + was discovered as reagent ion unexpectedly from our previous study, where NMP was emitted from a high efficiency particulate air filter (HEPA filter, model 12144, Pall Gelman) and ionized by the SXR ionizer. Compared to the proton affinity (PA) of H 2 O (691.2 kJ·mol –1 ), the PA of NMP (923.5 kJ·mol –1 ) is much higher.…”

“…Compared to the proton affinity (PA) of H 2 O (691.2 kJ·mol –1 ), the PA of NMP (923.5 kJ·mol –1 ) is much higher. Thus, NMPH + is more selective to compounds with high PA such as ammonia and amines . This minimizes background signals introduced by gaseous volatile organic compounds.…”

“…Thus, NMPH + is more selective to compounds with high PA such as ammonia and amines. 44 This minimizes background signals introduced by gaseous volatile organic compounds. Meanwhile, the "n" for (NMP) n H + is easier to adjust and maintain than that for (H 2 O) n H + .…”