BACKGROUND

1. Field

The present disclosure relates to spectrometry, and more particularly to ion-mobility spectrometry.

2. Description of Related Art

Ion-mobility spectrometers ionize gas-phase molecules, e.g., using a radioactive source located at the beginning of an analyzer flight tube. A population of these ions is then driven toward a detector. An electric field forces the ions forward through an opposing gas bath (the buffer gas) at atmospheric pressure. The time required to reach the detector is a function of ion mass to charge ratio (m/z) and collision cross-section, which together form a term known as Ko. This function is characteristic for a given ion.

The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved systems and methods for spectrometry. This disclosure provides a solution for this need.

SUMMARY

An ion-mobility spectrometer system includes a housing with an upstream end, a downstream end, and a drift region defined along a longitudinal axis through the housing between the upstream and downstream ends. A tandem ion source is included at the upstream end of the housing. The tandem ion source includes a first ionizer that is operatively connected the housing to supply ions at the upstream end, and a second ionizer that is operatively connected to the housing to supply ions at the upstream end. The first and second ionizers are both situated upstream of the drift zone relative to an ion flow path through the drift zone. An electric field generator is operatively connected to the housing to drive ions through the drift zone in a direction from the upstream end toward the downstream end. A detector is mounted at the downstream end of the housing for detecting ions from the drift zone reaching the detector. The second ionizer is a radioactive ionizer mounted to the housing at the upstream end positioned to direct irradiated ions radially into the housing relative to the longitudinal axis.

The first and second ionizers can both be located upstream of the electric field generator without any electric field generator between the first and second ionizers. The electric field generator can include a series of annular electrodes spaced apart axially along the drift zone, with a flow path for ions defined therethrough, wherein none of the annular electrodes is located between the first and second ionizers. The first ionizer can be a photoionizer/photofragmenter mounted to the housing on an upstream side of the drift zone, positioned to direct photons axially into the housing along the longitudinal axis. The second ionizer can be a63Ni ionizer. The63Ni ionizer can be mounted in a side passage of the housing that includes a gas inlet upstream of the63Ni ionizer, wherein the side passage meets the ion flow path in a radial direction. A wire grid can traverse the side passage downstream of the63Ni ionizer, wherein the wire grid is connected to a power circuit as an electrode, and the power circuit includes a switch for selectively activating and deactivating ion flow from the63Ni ionizer.

A method of ion-mobility spectrometry includes continuously ionizing molecules in an ionization zone with an ionizer upstream of a drift zone, directing photons from a photoionizer/photofragmenter into the ionization zone, wherein the photoionizer/photofragmenter is located upstream of the drift zone, driving ions generated by the ionizer and the photoionizer/photofragmenter through the drift zone with an electrical field, and selectively counteracting the ionizer with a wire grid electrode so that only the photoionizer/photofragmenter ionizes. The method includes detecting ions reaching a detector downstream of the drift zone to identify analytes in the ions.

Directing photons from the photoionizer/photofragmenter can include fragmenting ions ionized by the ionizer. Directing photons from the photoionizer/photofragmenter can include ionizing molecules that the ionizer cannot effectively ionize. The method can include deactivating the photoionizer/photofragmenter so that only the ionizer ionizes. The method can include activating and deactivating the photoionizer/photofragmenter at a rate that is faster than an expected dwell time of a predetermined analyte.

These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.

