Selected ion flow tube: Difference between revisions
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The '''selected ion flow tube''', '''SIFT''', technique is a fast flow tube | The '''selected ion flow tube''', '''SIFT''', technique is a fast flow tube method for the study of the reactions of [[ion|ions]] (positive or negative) with atoms and molecules under truly thermalised conditions over a wide range of temperature. It has been extensively used to study ion-[[ion]] chemistry over a 20-year period has been crucial to the advancement and understanding of these interesting topics. Recently it has been developed as a very sensitive analytical technique '''SIFT-MS selected ion flow tube mass spectrometry''' for the quantification of trace gases in air and in human breath down to the ppb level in real time using [[chemical ionisation]]. | ||
===Instrumentation=== | ===Instrumentation=== | ||
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'''The SIFT apparatus''' | '''The SIFT apparatus''' | ||
In the SIFT apparatus the ions are created in an ion source which is external to the flow tube. The ions are then extracted from the ion source, selected according to their mass-to-charge ratio using a quadrupole mass filter and injected into a flowing carrier gas (usually helium at a pressure of 0.5 Torr) via a small orifice ( ~1 mm diameter). | In the SIFT apparatus the ions are created in an [[ion source]] which is external to the flow tube. The ions are then extracted from the ion source, selected according to their mass-to-charge ratio using a [[quadrupole]] mass filter and injected into a flowing carrier gas (usually helium at a pressure of 0.5 Torr) via a small orifice ( ~1 mm diameter). | ||
The carrier gas is inhibited from entering the quadrupole mass filter chamber by injecting it into the flow tube through a Venturi-type inlet at near-supersonic velocity in a direction away from the orifice. In this way a swarm of a single ion species thermalised at the same temperature as the carrier gas are convected along the flow tube ( ~1 m long), sampled by a downstream pinhole orifice, mass analysed and counted by a differentially-pumped quadrupole mass spectrometer system. | The carrier gas is inhibited from entering the quadrupole mass filter chamber by injecting it into the flow tube through a Venturi-type inlet at near-supersonic velocity in a direction away from the orifice. In this way a swarm of a single ion species thermalised at the same temperature as the carrier gas are convected along the flow tube ( ~1 m long), sampled by a downstream pinhole orifice, mass analysed and counted by a differentially-pumped quadrupole [[mass spectrometer]] system. | ||
