AMMONIA AS A MODIFIER IN ION MOBILITY SPECTROMETRY: EFFECTS ON ION MOBILITIES AND POTENTIAL AS A SEPARATION TOOL
A commercial ammonia solution was introduced in the buffer gas of an ion mobility spectrometer and the mobilities of tetramethylammonium (TMA), tetraethylammonium (TEA), tetrapropylammonium (TPA), and tetrabutylammonium (TBA) ions, tribenzylamine (TBzA), tributylamine (TBtA), 2,4-dimethyl pyridine (...
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| Autores principales: | , , |
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| Lenguaje: | English |
| Publicado: |
Sociedad Chilena de Química
2014
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| Materias: | |
| Acceso en línea: | http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072014000100032 |
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| Sumario: | A commercial ammonia solution was introduced in the buffer gas of an ion mobility spectrometer and the mobilities of tetramethylammonium (TMA), tetraethylammonium (TEA), tetrapropylammonium (TPA), and tetrabutylammonium (TBA) ions, tribenzylamine (TBzA), tributylamine (TBtA), 2,4-dimethyl pyridine (2,4-lutidine), 2,6-di-tert-butyl pyridine (DTBP), serine, atenolol, and valinol decreased depending on their structures. Electrospray ionization-ion mobility spectrometry-quadrupole mass spectrometry was used in these experiments. Analyte ion mobilities decreased to different extents with the amount of ammonia introduced in the mobility spectrometer. When the amount of ammonia increased from 0.0 to 22 mmol m-3 (with a concomitant concentration of water of 106 mmol m-3), percentage reductions in mobilities were: -4.8% (serine), -1.9% (reactant ions), -1.1% (TBtA), -0.9% (TBzA), -0.5% (TEA), -0.4% (valinol and TBA), -0.3% (TEA, TMA, and 2,4-lutidine), and 0% (atenolol and DTBP). These selective variations in mobilities were due to formation of large analyte ion-ammonia-water clusters. The small change in mobility of tetraalkylammonium ions, TBzA, TBtA, atenolol, and DTBP with the introduction of ammonia into the buffer gas was explained by steric hindrance of bulky substituents which shielded the positive charge of the ion from the attachment of ammonia and water molecules, and delocalized the positive charge. Ammonia in the buffer gas produced ion clusters with one or two ammonia molecules in compounds with little steric hindrance such as serine. At concentrations of ammonia of 4.4 mmol m-3 or higher (at 150°C), ligand-saturation with ammonia and water molecules occurred on the positive charge of some ions; when the positive charge saturated, no significant reductions in ion mobility occurred when increasing the concentration of ammonia in the buffer gas. |
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