Ion mobility separator

IM-TOF MALDI positive ion mode Full-scan MS Ion mobility separation (29)... 

Trim P, Henson C, Avery J, McEwen A, Snel M, Claude E, Marshall P, West A, Princivalle A, Clench M (2008) Matrix-assisted laser desorption/ionization-ion mobility separation-mass spectrometry imaging of vinblastine in whole body tissue sections. Anal Chem 80 8628-8634. doi 10.1021/ac8015467... 

Ion mobility can add an extra dimension of separation when coupled to a mass analyzer. Ion mobility spectrometry (IMS) separates ions according to their interactions with a buffer gas, in addition to differences in their m/z ratios. This can provide separation of ions (i.e., isobaric or conformational isomers), which cannot be accomplished using traditional mass analyzers. It can also be used to reduce interfering chemical noise. Ion mobility separates ions based on how long they take to migrate... 

Because IMS is a method that separates gas phase ions through collisions with a buffer gas, all analytes must be transported from the sample matrix and converted to a gas phase ion before ion mobility separation and detection can be performed. Thus, the type of introduction method largely depends on the physical characteristics of the analyte. The remainder of this chapter is divided into four sections based on the characteristics of the sample vapor, semivolatile, aqueous, and solid. While these categories are somewhat arbitrary with significant sample overlap, it is useful to think of volatile samples as those compounds that exist or partially exist as vapors under ambient temperature and pressure semivolatile samples as those compounds that can be volatilized but have vapor pressures too low to detect by IMS under ambient temperature and pressure aqueous samples as those compounds that are not volatile but can be dissolved in water and solid samples as compounds not in a solution. Table 3.1 lists a number of example analytes according to the categories discussed in this chapter. 

The process of converting a swarm of gas phase ions into an electrical signal that provides both arrival time information and amplitude information is known as ion detection. The ion detector is typically located after the ion mobility separation cell and has a number of ideal requisites to accomplish the transduction of mobility-separated ions in a manner that minimizes loss of sensitivity and IMS resolving power. 

The resolution of an ion mobility separation depends on both the resolving power Rp and the separation selectivity a of the IMS system. Resolution R determines how well two peaks, with drift times of tj and t2 and peak widths of Wj and W2 can be separated from one another and is defined as... 

FIGURE 8.9 Selectivity induced by cation adduction. Ion mobility separation of methyl-p-D-galactopyranoside from its isomer methyl-a-D-galactopyranoside using different cation adducts. (From Dwivedi et al., Rapid resolution of carbohydrate isomers by electrospray ionization ambient pressure ion mobility spectrometry-time-of-flight mass spectrometry (ESI-APIMS-TOFMS), J. Am. Soc. Mass Spectrom. 2007, 18, 1163-1175. With permission.)... 

In summary, ion mobility separations occur by a variety of methods. In all cases, there is an instrumental scan parameter that controls the separation of the ion. For example, in the drift tube spectrometers, it is the arrival time of the ion for the aspiration spectrometers, it is the position of the faraday plates for the mobility analyzers, it is the strength of the orthogonal voltage and for the DMSs, it is the compensation voltage. The relative value of these scan parameters for two ions is called the separation factor a, and the resolving power of a spectrometer is determined by the ratio of the scan parameter to the width of the scan parameters for a packet of ions. 

An example of IMS-TrapMS analysis is shown in Figure 9.12. Spectrum 1 illustrates the ion mobility separation of three isomers (hesperidin, neohesperidin, and rutin) adducted with silver. Spectrum 2 shows the overlaid ion mobility spectra of the respective standards. Through the use of single-mobility monitoring, the ions contained in the drift time windows (a), (b), and (c) were fragmented to produce the mass spectra shown in 1(a), 1(b), and 1(c), respectively. Shown in bold text in 1(a) and 1(b), the ions 409 and 411 may be used to confirm the presence of either hesperidin or neohesperidin. However, the IMS separation prior to mass analysis is necessary to distinguish conclusively among the three isomers. 

Thus, IMS can serve as a stand-alone instrument in medical and biological applications for which only limited information from a small number of compounds is required. Ion mobility separation can be used to preseparate or filter interfering compounds prior to MS analysis or serve as a means of distinguishing between isomers based on structural differences. As mentioned, mobility data can also be used to determine the stereoscopic conformation of macromolecules and can thus serve as a means for assessing their biologic activity. 

Hoaglund-Hyzer, C.S., Lee, YJ., Counterman, AJi., Clenuner, D.E., Coupling ion mobility separations, coUisional activation techniques, and multiple stages of MS for analysis of complex peptide mixtures. Anal. Chem. 2002, 74, 992. 

Shvartsburg, A. A., Mashkevich, S.V., Smith, R.D., Feasibility of higher-order differential ion mobility separations using new asymmetric waveforms. J. Phys. Chem. A 2006,110, 2663. 

Wildgoose, J.L. Giles, K. Pringle, S.D. Koeniger, S.L. Valentine, S.J. Bateman, R.H. Clemmer, D.E. A comparison of travelling wave and drift tube ion mobility separations. Proc. 54th ASMS Conference on Mass Spectrometry and Allied Topics, Seattle, WA, May 28-June 1, 2006, ThP 64.AQ... 

Trim, P.J. Avery, J.L. McEwen, A. Snel, M.F. Claude, E. Marshall, P.S. West, A. Princivalle, A.P. Clench, M. MALDI-ion mobility separation-MS imaging of Vinblastine and its metabolites in rat tissue. Proc. 56th ASMS Conference on Mass Spectrometry and Allied Topics, Denver, CO, June 1-5, 2008, MP 130. 

Eckers, C. Laures, A.M. Giles, K. Major, H. Pringle, S. Evaluating the utihty of ion mobility separation in combination with high-pressure liquid chromatography/mass spectrometry to facihtate detection of trace impurities in formulated drug products. Rapid Commun. Mass Spectrom. 2007, 21,1255-1263. 

Mass spectrometrists have always been concerned with the measurement of the mass and intensity of analyte ions. Investigation/utilization of the shapes of molecules is now possible with ion mobility techniques that utilize differences in the cross sections of ions as they move through a gas. Think in terms of two pieces of paper, one crumpled and the other flat. If dropped at the same time, the crumpled one will hit the floor first because it will encounter less air resistance than the flat piece. A similar situation applies to ions with different shapes as they travel through a gas. Although ion mobility has been examined with home-built instruments for years, only recently has this type of analyzer become available commercially. There are two significantly different types, the high-field asymmetric waveform ion mobility spectrometer (FAIMS) and the ion mobility separator (IMS). The FAIMS separator is placed between the ion source and the analyzer, while the IMS cell is located between the analyzers of an MS/MS instrument. 

The typical time bin of an ion mobility separation is in the millisecond range. Because this time window is substantially larger than the duration of the TOF measuremenL many single mass spectra can be recorded during one IMS separation. Under optimal conditions the overall transmission efficiency is close to that achieved without IMS. Depending on the complexity of the sample, limits of detection in the subfemtomolar range are achieved in the MALDI-IMMS analysis of peptides. 

In ion mobility separation (IMS), ions move in a medium-pressure chamber (about 1 mmHg). Ions with... 

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