An ion filter for filtering ions in a gas sample. The ion filter has a first ion channel for filtering ions from a target chemical in the gas sample. The ion filter has a second ion channel for filtering ions from the target chemical in the gas sample. The second ion channel is separated from the first ion channel. A temperature control region is in thermal contact with the first and second ion channels for controlling a difference in temperature between the first and second ion channels. A method of filtering ions from a target chemical in a gas sample is also provided.