Time-of-flight (TOF) mass spectrometer without pulses of any kind, with continuous ion introduction

Abstract

A new concept for time-of-flight (TOF) mass spectrometry is presented. Currently, TOF instruments use pulsed ion introduction with a 10 ns or so pulse width, followed by a waiting period roughly 100 μs. Accordingly, the sample is under excitation in 10 −4 part of the total measuring time, which limits the sensitivity of the method. Secondly, the ion bunch generated is strongly confined, which gives rise to space charge problems deteriorating the signal intensity and the mass resolution. The concept presented here uses a continuously operating ion source and a special dual modulation technique [Patent pending]. The expected advantages are higher sensitivity and minor space charge limitations. The space charge limitations are obviously easier if the charges are distributed uniformly in an ion beam rather than being confined in a bunch. Moreover, the necessary detection bandwidth is as low as some hundred Hz, which enables to operate the electrometer electronics with amplification as high as 10 10 V/A. Because of the high signal level, it was possible to omit any electrostatic mirror configuration for bunching the ions. Rather a cylindrical energy filter was installed to remove the ions with undesired energies. The drift tube is roughly 2 m long. The measurement is controlled by a PC via a home made board. The data are collected and the fast Fourier transformation is performed by the software. The objective of the experimental setup is to demonstrate the operation of this novel measuring principle. The analytical capabilities in present stage are admittedly poor, however its potential improvement is far less limited by physics than in the case of the pulsed TOF techniques.