Ion mobility spectrometer including spaced electrodes for filtering

Detection apparatus comprising:

• spaced electrodes;
• and
• a voltage source;
• wherein the voltage source is arranged to apply both low and high alternating fields to the electrodes such as to produce separate indications of both the low and high field mobility of detected ions,
• wherein the detection apparatus further comprises:
• a processor arranged to provide an indication of the nature of the detected ions using both the mobility indications.

A method of detecting ions, comprising:

• supplying analyte ions for detection between two electrodes;
• applying two different fields between the electrodes at different times, one field being a relatively low symmetric alternating field that increases in magnitude over a time exceeding the period of the alternating field, the other field being a relatively high asymmetric field sufficient to cause high field differential mobility effects in the ions;
• collecting ions passed through the electrodes during the application of both fields;
• and
• providing an indication of the nature of the ions from signals produced by the collected ions during both the low and high fields.

A spectrometer comprising:

• an inlet for an analyte substance;
• and
• an ionization region arranged to produce ions of the substance and to supply those ions to an electric field region;
• wherein the electric field region is switchable between two different fields, namely a relatively low magnitude alternating field that varies in magnitude over multiple periods and an asymmetric alternating field of sufficiently high magnitude to cause differential mobility effects.

Detection apparatus comprising:

• a housing having a first end and a second end opposite said first end;
• an inlet located in the housing at the first end for admitting an analyte substance;
• an ionization region located near the first end where an analyte substance admitted to the housing is ionized;
• a pair of spaced electrodes located in the housing intermediate the first and second ends thereof;
• a voltage source oscillator that is selectively operable to apply first and second different electrical fields to the electrodes;
• a collector located in the housing near the second end that collects ions passed through the electrical field applied to the electrodes and produces an output signal that varies as ions of different mobilities are passed through the electrodes or are captured between them;
• and
• a processor responsive to the output signal to provide an indication of the ions detected by the collector.