Improving mass spectrometers' sensitivity
Scientists have developed a new tool that improves the sensitivity of certain mass spectrometers at the William R. Wiley Environmental Molecular Sciences Laboratory, Richland, Wash.
The device is known as the electrodynamic ion funnel. It uses a series of conductive ring electrodes of increasingly smaller internal diameter to which radio frequency and direct current voltages are applied. This combination causes ions to be confined and more effectively focused and transmitted.
Without the ion funnel, significant ion losses occur when ions pass from regions of high pressure to lower pressure regions where the mass spectrometer can function.
The ion acceptance characteristics of the device are decoupled from the ion emittance. This means that ion clouds of arbitrarily large size can be focused as they are transported through the ion funnel, reversing the normal ion cloud expansion that takes place due to the mutual repulsion of similarly charged ions.
"The ion funnel serves to greatly increase ion transmission, particularly from higher pressure ion sources, such as those based on electrospray ionization (ESI). Forty-to 80-fold gains in sensitivity for ESI are routinely realized for conventional mass spectrometers retrofitted with an ion funnel," said the device's inventor, Richard Smith.
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This article originally appeared in the 08/01/1999 issue of Environmental Protection.
Gerald F. Connell, ChE is a consultant, retired after 30 years with Capital Controls Group, Severn Trent Service Inc., Colmar, Pa. Mr. Connell is author of "The Chlorination/Chloramination Handbook," published by the American Water Works, and a forthcoming "Chlorination/Dechlorination Handbook" to be published by WEF.