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Reagent assessment for detection of ammonium ion‐molecule complexes
Author(s) -
Gregory Kerin E.,
Ostrinskaya Alla,
Kunz Roderick R.
Publication year - 2013
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6746
Subject(s) - chemistry , reagent , molecule , dissociation (chemistry) , inorganic chemistry , ammonium , mass spectrometry , electrospray ionization , chemical ionization , ion , chromatography , ionization , organic chemistry
RATIONALE Ammonia (NH 3 ) is an important chemical target in sensor applications such as trace explosives detection of ammonium nitrate (NH 4 NO 3 ) and environmental monitoring. Ion‐molecule reagent chemistries show potential to increase sensitivity in detection systems relying on atmospheric pressure ionization (API) of reagent‐ammonium (M + NH 4 + ) complexes. Gas‐phase reagent selection assessment is based on mass spectrometric (MS) determination of binding constants relative to competitive ions and critical energies for ion‐molecule complex dissociation. METHODS Eight ammonium complexation reagents were identified and gas‐phase ion‐molecule interactions were studied using electrospray ionization. Binding constants were determined, in Log( K ), using the competition method for one host molecule with three guests (NH 4 + , Na + , and K + ) in single quadrupole MS. Critical energy determination was based on calibration of threshold activation voltage using collision‐induced dissociation (CID) tandem mass spectrometry (MS/MS). RESULTS This assessment informs selective binding affinity and intrinsic ion‐molecule critical energy for dissociation. Relative NH 4 + binding affinity was highest for sucrose and 4‐ tert ‐butylcalix[6]arene, while 4‐ tert ‐butylcalix[6]arene and methyl acetoacetate showed the highest preferential binding of NH 4 + versus Na + and K + . The intrinsic critical energy for NH 4 + binding was highest for crown ethers, tetraglyme and methyl acetoacetate. CONCLUSIONS An MS‐based framework was developed to quantitatively assess API ion‐molecule reagent chemistries based on ammonium selectivity versus competing ions, and intrinsic ammonium binding strength and complex survivability for detection. Methyl acetoacetate is an attractive ammonium reagent for vapor‐phase API techniques given its high vapor pressure, preferential selectivity, and high critical energy for dissociation. Copyright © 2013 John Wiley & Sons, Ltd.