Chemical standards in ion mobility spectrometry

Abstract

In ion mobility spectrometry (IMS), reduced mobility values (K0) are used as a qualitative measure of gas phase ions, and are reported in the literature as absolute values. Unfortunately, these values do not always match those collected in the field. One reason for this discrepancy is that the buffer gas may be contaminated with moisture or other volatile compounds. In this study, the effect of moisture and organic contaminants in the buffer gas on the mobility of IMS standards and analytes was investigated for the first time using IMS directly coupled to mass spectrometry. 2,4-dimethylpyridine, 2,6-di-tert-butyl pyridine (DTBP), and tetrabutylammonium, tetrapropylammonium, tetraethylammonium, and tetramethylammonium chlorides were used as chemical standards. In general, the mobility of IMS standard product ions was not affected by small amounts of contamination while the mobilities of many analytes were affected. In the presence of contaminants in the buffer gas, the mobility of analyte ions is often decreased by forming ionmolecule clusters with the contaminant. To ensure the measurement of accurate reduced mobility values, two IMS standards are required: an instrument and a mobility standard. An instrument standard is not affected by contaminants in the buffer gas, and provides an accurate measurement of the instrumental parameters, such as voltage, drift length, pressure, and temperature. The mobility standard behaves like an analyte ion in that the compound's mobility is affected by low levels of contamination in the buffer gas. Prudent use of both of these standards can lead to improved measurement of accurate reduced mobility values.

Computational fluid dynamics-Monte Carlo method for calculation of the ion trajectories and applications in ion mobility spectrometry

“…IMS is a well-known method to analyze chemical substance using gas-phase mobility in a weak electric field [14][15][16], and is more and more used in the detection of explosives, drugs, chemical warfare agents, biological and medical samples [17][18][19][20][21][22][23][24][25]. Unlike the mass spectrometry [26,27], which operates in vacuum, IMS detects chemical compounds at atmospheric pressure.…”

Ion Mobility-Mass Spectrometry with a Radial Opposed Migration Ion and Aerosol Classifier (ROMIAC)

“…C2-C8 and C12 TAAX monomer ions were used as instrument calibration standards, as their reduced mobilities are unaffected by trace carrier gas contaminants and temperature [5,6,7]. TAAX monomer ion mobility values are from [6].…”

Ammonia as a Modifier in Ion Mobility Spectrometry: Effects on Ion Mobilities and Potential as a Separation Tool

“…19 Ion mobility spectrometry using buffer gas modifiers separates ions in a gas phase by exposing ions to a polar modifier. [20][21][22] These modifiers enhance ion-molecule interaction forces. When polar modifiers are introduced into a buffer gas, they interact with the analytes ions depending on the ion structures and steric hindrance of the atoms bearing the charges; this interaction leads to the formation of clusters of different sizes that spend different times inside the drift tube.…”