For the first tlme, an atmospheric pressure ionizatlon source was coupled to a tlme-of-flight mass spectrometer. A corona discharge was used to produce Ions at ambient pressure. The Ions were then expanded Into the vacuum through an orlflce, formlng a supersonlc beam perpendlcular to the dlrection of acceleratlon. Ions were repelled Into the filght tube. Thls supersonlc expanslon narrowed the ions' veloclty dlstrlbutlon and In turn improved the mass resolutlon, whlch was approximately 500 for protonated dlmethyi methyl phosphonate dimer ions ( m / r = 249). The perpendlcular Ion beam lntroductlon scheme Is potentlaily more sensltlve than the on-axis conflguratlon. Factors affecting the sensitivity and mass range are discussed.
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