Tandem Ion Modulator for Characterizing Larger Biomolecules in a Differential Mobility Spectrometer

Abstract

The tandem differential mobility spectrometer (DMS)-ion modulator instrument provides improved resolution relative to traditional DMS for molecules with larger masses. The instrument includes multiple ion-bunching electrodes, each with an AC field synchronized to the transit time of the ion flow which is positioned downstream of a DMS. The ion bunching electrodes produce each a mobility-dependent modulation of the ion current. The ratio of AC to DC current provides a measure of the mobility of a large ion, even if it has little differential mobility, thereby extending the useful range of mobility characterization of a DMS system. The instrument does not require high voltages or high frequencies. Modulation before DMS separation or between tandem DMS separations produces a variable range of analyte and reactant ion densities as well as spatially separating negative and positive ions to reduce ion recombination.

Description

BACKGROUNDField of the Invention[0001]This disclosure relates to analytical machinery and the identification and separation of molecules.Background of the Invention[0002]Differential mobility spectrometers (hereinafter, “DMS”), also called field asymmetric ion mobility spectrometers (FAIMS) operate by applying an asymmetric transverse alternating current (hereinafter “AC”) field to a stream of ions moving in a carrier gas, for example, air. The asymmetric field has a high field portion which is on for a short duration, and a low field portion of opposite polarity which is on for a longer duration. Unlike vacuum ion sorting methods which operate in the ballistic flow regime (no atom collisions), for example, mass spectrometers, ion mobility spectrometers operate in the viscous flow regime (e.g. atmospheric pressure). This means that molecules are rapidly colliding and ions in an electric field (E) experience a terminal velocity (v) that depends on their collision cross section, which...

AI Technical Summary

Benefits of technology

[0006]The longitudinal AC field may cause ions to bunch by alternately pushing and pulling ions as they pass through the modulator. High mobility ions bunch more readily and produce a larger AC ion current modulation. Low mobility ions are more difficult to bunch and thus produce a smaller AC ion current modulation relative to the direct current which is the ion concentration. Thus, the mobility (or average mobility) of the differential mobility spectrometer output may be measured by comparing the ratio of the AC to the direct current.

Problems solved by technology

Low mobility ions are more difficult to bunch and thus produce a smaller AC ion current modulation relative to the direct current which is the ion concentration.

Images