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Ionization of 2-nonanone, cyclopentanone, acetophenone, pyridine, and di-tert-butylpyridine (DTBP) in a corona discharge (CD) atmospheric pressure chemical ionization (APCI) ion source was studied using ion mobility (IMS) and time-of-flight mass spectrometry (TOF–MS). The IMS and MS spectra were recorded in the absence and presence of ammonia dopant. Without NH3 dopant, the reactant ion (RI) was H+(H2O) n , n = 3,4, and the MH+(H2O) x clusters were produced as product ions. Modeling of hydration shows that the amount of hydration (x) depends on basicity of M, temperature and water concentration of drift tube. In the presence of ammonia (NH4 +(H2O) n as RI) two kinds of product ions, MH+(H2O) x and MNH4 +(H2O) x , were produced, depending on the basicity of M. With NH4 +(H2O) n as RI, the product ions of pyridine and DTBP with higher basicity were MH+(H2O) x while cyclopentanone, 2-nonanone, and acetophenone with lower basicity produce MNH4 +(H2O) x . To interpret the formation of product ions, the interaction energies of M–H+, H+–NH3, and H+–OH2 in the M–H+–NH3 and M–H+–OH2 and M–H+–M complexes were computed by B3LYP/6-311++G­(d,p) method. It was found that for a molecule M with high basicity, the M–H+ interaction is strong leading in weakening of the H+–NH3, and H+–OH2 interactions in the M–H+–NH3 and M–H+–OH2 complexes.

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Protonation, hydration and cluster formation of ammonia, formaldehyde, formic acid, acetone, butanone, 2-ocatanone, 2-nonanone, acetophenone, ethanol, pyridine and its derivatives were studied by IMS-TOFMS technique equipped with a corona discharge ion source. It was found that tendency of the protonated molecules, MH + , to participate in hydration or cluster formation depends on the basicity of M. The molecules with higher basicity were hydrated less than those with lower basicity. The mass spectra of the low basic molecules such as formaldehyde exhibited larger clusters of MnH + (H2O)n while for compounds with high basicity such as pyridine only MH + and MH + M peaks were observed. The results of DFT calculations confirm that enthalpies of hydrations and cluster formation decrease as basicities of the molecules increases. Using comparison of mass spectra of formic acid, formaldehyde, and ethanol, effect of structure on the cluster formation was investigated. Formation of symmetric (MH + M) and asymmetric protonbound dimers (MH + N) was studied by ion mobility and mass spectrometry techniques. Both theoretical and experimental results shows that asymmetric dimers are formed more easily between molecules (M and N) with comparable basicity. As the basicity different between M and N increases, the enthalpy of MH + N formation decreases.

A simple, fast, and inexpensive method was developed for detecting heavy metals via the ion mobility spectrometry (IMS) in the negative mode. In this method, Cl(-) ion produced by the thermal ionization of NaCl is employed as the dopant or the ionizing reagent to ionize heavy metals. In practice, a solution of mixed heavy metals and NaCl salts was directly deposited on a Nichrome filament and electrically heated to vaporize the salts. This produced the IMS spectra of several heavy-metal salts, including CdCl2, ZnSO4, NiCl2, HgSO4, HgCl2, PbI2, and Pb(Ac)2. For each heavy metal (M), one or two major peaks were observed, which were attributed to M·Cl(-) or [M·NaCl]Cl(-)complexes. The method proved to be useful for the analysis of mixed heavy metals. The absolute detection limits measured for ZnSO4 and HgSO4 were 0.1 and 0.05 μg, respectively.