Preliminary Design Considerations and Characteristics of an Inductively Coupled Plasma-Time-of-Flight Mass Spectrometer

Abstract

Multielement analysis by means of plasma source mass spectrometry has evolved over the past decade primarily through the use of the quadrupole mass analyzer. In the present research a time-of-flight mass spectrometer (TOFMS) has been designed, built, and tested with an inductively coupled plasma (ICP) supported with argon. The TOEMS offers higher speed, higher ion transmission, and measurement of all masses in one cycle of mass analysis. This paper outlines the considerations that were used to devise an appropriate geometry for the TOFMS, considering the known characteristics of the ICP ion source and the expected behavior of an ICP-MS interface. When linear and right-angle geometries are compared, the right-angle TOFMS seems far more appropriate as a mass analyzer in an LCP-MS instrument. The right-angle TOFMS was interfaced to an ICP and its preliminary characteristics have been evaluated. The mass spectrometer exhibits excellent speed and unit-mass resolution for the elements. However, the initial sensitivity is lower than originally estimated, probably because of poor ion transport from the ICP into the TOFMS. In addition, the ions produced from the plasma gas (argon) saturate the microchannelplate detector, prompting the implementation of a deflection scheme to remove much of the Ar +. These initial observations as well as future endeavors are presented.