Nanoclusters formation in ion mobility spectrometry and change separation selectivity of picoline isomers

2018

J Mass Spectrom

Ion mobility spectrometry (IMS) is an analytical technique used for fast and sensitive detection of illegal substances in customs and airports, diagnosis of diseases through detection of metabolites in breath, fundamental studies in physics and chemistry, space exploration, and many more applications. Ion mobility spectrometry separates ions in the gas-phase drifting under an electric field according to their size to charge ratio. Ion mobility spectrometry disadvantages are false positives that delay transportation, compromise patient's health and other negative issues when IMS is used for detection. To prevent false positives, IMS measures the ion mobilities in 2 different conditions, in pure buffer gas or when shift reagents (SRs) are introduced in this gas, providing 2 different characteristic properties of the ion and increasing the chances of right identification. Mobility shifts with the introduction of SRs in the buffer gas are due to clustering of analyte ions with SRs. Effective SRs are polar volatile compounds with free electron pairs with a tendency to form clusters with the analyte ion. Formation of clusters is favored by formation of stable analyte ion-SR hydrogen bonds, high analytes' proton affinity, and low steric hindrance in the ion charge while stabilization of ion charge by resonance may disfavor it. Inductive effects and the number of adduction sites also affect cluster formation. The prediction of IMS separations of overlapping peaks is important because it simplifies a trial and error procedure. Doping experiments to simplify IMS spectra by changing the ion-analyte reactions forming the so-called alternative reactant ions are not considered in this review and techniques other than drift tube IMS are marginally covered.

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Section: Applications Of Mobility Shifts Upon Injection Of Buffer Gasmentioning

confidence: 99%

Buffer gas additives (modifiers/shift reagents) in ion mobility spectrometry: Applications, predictions of mobility shifts, and influence of interaction energy and structure

2018

J Mass Spectrom

“…We separated amino acids, drugs, and tetraalkylammonium ions superimposed on the mobility spectrum using SRs such as ethyl lactate, nitrobenzene, 2‐butanol, trifluoromethyl benzyl alcohol, methyl 2‐chloropropionate, water, ammonia, and methanol in the drift gas . In 2014, Campbell et al explained that the molecular weight of SRs is not the primary factor for mobility changes upon introduction of SRs in the drift gas but the binding energy and steric hindrance at the charge site of analyte ions, and this information was applied to separate picoline isomers with 2‐butanol . Before, most researchers explained mobility shifts based on the increase of the collision cross section of the analytes upon clustering with SRs .…”

Section: Introductionmentioning

confidence: 99%

Caffeine and glucosamine mobility shifts by adduction with 2‐butanol depended on interaction energy, charge delocalization, and steric hindrance in ion mobility spectrometry

Meza-Morelos

2017

J Mass Spectrom

Ion mobility spectrometry (IMS) is an analytical technique that separates gas-phase ions drifting under an electric field according to their size to charge ratio. We used electrospray ionization-drift tube IMS coupled to quadrupole mass spectrometry to measure the mobilities of glucosamine (GH ) and caffeine (CH ) ions in pure nitrogen or when the shift reagent (SR) 2-butanol was introduced in the drift gas at 6.9 mmol m . Binding energies of 2-butanol-ion adducts were calculated using Gaussian 09 at the CAMB3LYP/6-311++G(d,p) level of theory. The mobility shifts with the introduction of 2-butanol in the drift gas were -2.4% (GH ) and -1.7% (CH ) and were due to clustering of GH and CH with 2-butanol. The formation of GBH was favored over that of CBH because GBH formed more stable hydrogen bonds (83.3 kJ/mol) than CBH (81.7 kJ/mol) for the reason that the positive charge on CH is less sterically available than on GH and the charge is stabilized by resonance in CH . These results are a confirmation of the arguments used to explain the drift behavior of these ions when ethyl lactate SR was used (Bull Kor Chem Soc 2014, 1023-1028). This study is a step forward to predict IMS separations of overlapping peaks in IMS spectra, simplifying a procedure that is trial and error by now.

“…[23] Nevertheless, these models are not comprehensive, can only be applied to predict the mobility in homologous series, and require further development because they do not consider SR-ion interaction energies and interaction site dependent energies, among other handicaps; these energies have been considered an important factor for mobility shifts. [22] Other applications used (S)-2-butanol to separate overlapping picoline isomers by nanocluster formation [24] and acetonitrile as a SR in the carrier gas to separate paralytic shellfish toxins epimeric pairs by high-field asymmetric waveform IMS. Auerbach et al predicted compensation voltages in DMS using linear regression of descriptors such as proton affinity and gas phase acidity of the SR molecules in a DMS-MS device; they used a homologous series of alcohols as the SR and a homologous series of 4-alkylbenzoic acids and a selection of 23 small molecules of high chemical diversity as the analytes.…”

Section: Introductionmentioning

confidence: 99%

“…Auerbach et al predicted compensation voltages in DMS using linear regression of descriptors such as proton affinity and gas phase acidity of the SR molecules in a DMS-MS device; they used a homologous series of alcohols as the SR and a homologous series of 4-alkylbenzoic acids and a selection of 23 small molecules of high chemical diversity as the analytes. [22] Other applications used (S)-2-butanol to separate overlapping picoline isomers by nanocluster formation [24] and acetonitrile as a SR in the carrier gas to separate paralytic shellfish toxins epimeric pairs by high-field asymmetric waveform IMS. [25] Here, we studied the mobility shifts produced in ethanolamine and valinol by the introduction of M as a buffer gas SR in IMS to establish the effects of adduct stabilities and the number of SR interaction sites in these shifts and to contribute to develop predictive models to choose SR for IMS separations of overlapping peaks.…”

Section: Introductionmentioning

confidence: 99%

Shift reagents in ion mobility spectrometry: the effect of the number of interaction sites, size and interaction energies on the mobilities of valinol and ethanolamine

Meza-Morelos

2016

J. Mass Spectrom.

Overlapping peaks interfere in ion mobility spectrometry (IMS), but they are separated introducing mobility shift reagents (SR) in the buffer gas forming adducts with different collision cross-sections (size). IMS separations using SR depend on the ion mobility shifts which are governed by adduct's size and interaction energies (stabilities). Mobility shifts of valinol and ethanolamine ions were measured by electrospray-ionization ion mobility-mass spectrometry (MS). Methyl-chloro propionate (M) was used as SR; 2-butanol (B) and nitrobenzene (N) were used for comparison. Density functional theory was used for calculations. B produced the smallest mobility shifts because of its small size. M and N have two strong interaction sites (oxygen atoms) and similar molecular mass, and they should produce similar shifts. For both ethanolamine and valinol ions, stabilities were larger for N adducts than those of M. With ethanolamine, M produced a 68% shift, large compared to that using N, 61%, because M has a third weak interaction site on the chlorine atom and, therefore, M has more interaction possibilities than N. This third site overrode the oxygen atoms' interaction energy that favored the adduction of ethanolamine with N over that with M. On the contrary, with valinol mobility shifts were larger with N than with M (21 vs 18%) because interaction energy favored even more adduction of valinol with N than with M; that is, the interaction energy difference between adducts of valinol with M and N was larger than that between those adducts with ethanolamine, and the third M interaction could not override this larger difference. Mobility shifts were explained based on the number of SR's interaction sites, size of ions and SR, and SR-ion interaction energies. This is the first time that the number of interaction sites is used to explain mobility shifts in SR-assisted IMS. Copyright © 2016 John Wiley & Sons, Ltd.