Atmospheric pressure ionization apparatus and method

An atmospheric pressure ionization apparatus includes a chamber, an ion inlet structure, an electrode, a sample emitter, and a gas passage. The ion inlet structure includes a sampling orifice. The electrode includes an electrode bore. An ionization region is defined between the ion inlet structure and the electrode. The flared structure is coaxially disposed about the ion inlet structure, and extends along an outward direction that includes a radial component relative to the sampling axis. The sample emitter is oriented at an angle to the sampling axis for directing a sample stream toward the ionization region. The gas passage directs a stream of gas from a gas source to the chamber. The flared structure and the wall cooperatively form an outward-directed portion of the gas passage that extends annularly about the sampling axis and along the outward direction. The gas flows through the outward-directed portion, around the flared structure, and toward the ionization region and the electrode bore.