Atmospheric pressure ionization ion mobility spectrometry

An API ion mobility spectrometer comprising:

• an elongated generally tubular body having an ion source end and an ion target end and a longitudinal axis extending between said ends;
• said body including a desolvation chamber adjacent said ion inlet end and a drift chamber adjacent said ion target end;
• an API ion source disposed at said ion source end for introducing ions and solvent into said desolvation chamber;
• a voltage source connected to apply a voltage differential to said ends of said body;
• said body including electrically conductive and resistive materials distributed along its length applying said voltage differential as an ion propulsion field acting in a first direction within said body along said longitudinal axis to propel ions from said ion source end to said ion target end;
• a drift gas inlet disposed at said ion target end for admitting drift gas to flow through said drift chamber and said desolvation chamber in opposition to the flow of ions;
• a barrier wall in said body extending transverse to said longitudinal axis and separating said drift chamber from said desolvation chamber;
• and
• an aperture in said barrier wall permitting flow of ions from said desolvation region into said drift chamber while restricting the flow of drift gas from said drift chamber to said desolvation region.

A method for ion mobility spectrometry comprising the steps of:

• injecting ions and solvent into a desolvation chamber at a first end of an axially extending ion accelerator body;
• applying an electrical field to the ion accelerator body to propel ions from the desolvation chamber and through a drift tube toward a second end of the body;
• flowing a drift gas from the second end of the body through the drift tube and desolvation region to the first end of the body;
• partially blocking the flow of drift gas from the drift tube to the desolvation chamber with a flow barrier, and
• providing a restricted flow of drift gas from the drift tube to the desolvation chamber through an aperture in the flow barrier.

A method for ion mobility spectrometry comprising the steps of:

• injecting ions into a first end of an axially extending ion accelerator body;
• applying an electrical field to the ion accelerator body to propel ions from the first end and through a drift tube toward a second end of the body;
• introducing a flow of drift gas into the body;
• flowing the drift gas from the second end of the body through the drift tube and desolvation region to the first end of the body;
• and
• varying the rate at which drift gas is introduced into the body in order to alter the selectivity of the ion mobility spectrum.