Microfabricated Quadrupole Mass Spectrometer With a Brubaker Prefilter

Microfabricated quadrupole mass spectrometers with Brubaker prefilters are demonstrated for the first time. Complete filters are assembled from two dies, each carrying two pairs of rods providing the prefilter and main filter sections. The rods are held in precision silicon mounts that are fabricated using wafer-scale deep reactive-ion etching and anodic bonding to glass substrates. Improvements to ion transmission are obtained by tuning the bias potential applied to the prefilter. The effect is explained in terms of a simple analytic theory for ion motion in the prefilter. Mass filtering with a range of m / z = 0-1200 and a resolution of m /¿ m ¿ 150 at 10% of peak height is demonstrated using 2-4-mm-long prefilter electrodes, 30-mm-long main electrodes (both of 650 ¿m diameter), and a radio-frequency drive at ¿6.5 MHz.