Sub-miniature ExB sector-field mass spectrometer

Abstract

A novel sub-miniature double-focusing sector-field mass spectrometer has been fabricated at the University of Minnesota using a combination of conventional machining methods and thin film patterning techniques typically used in the sensor technology industry. Its design is based on the mass separation capabilities of a 90° cylindrical crossed electric and magnetic sector-field analyzer with a 2-cm radius, which under proper conditions is able to effectively cancel the angular and chromatic dispersion of the ion beam, thus improving the resolving power of the instrument. Simulations using finite element analysis and computer modeling were employed to verify and optimize the performance of the proposed instrument before and during its fabrication. The prototype was able to attain a resolving power of 106 full-width at half-maximum (FWHM), a detection limit close to 10 parts per million, a dynamic range of 5 orders of magnitude and a mass range up to 103 Da. Its overall size, including the magnet assembly, is 3.5 cm wide, 6 cm long and 7.5 cm tall, it weighs 0.8 kg, and its power consumption was measured to be 2.5 W. The performance of the instrument was found to be comparable to that of commercial residual gas analyzers, at a fraction of the cost. All these characteristics make this miniature mass spectrometer suitable for portable and low-cost analytical instrumentation.