MEMS-Based Nanospray-Ionization Mass Spectrometer

An electrospray-ionization mass spectrometer (ESI-MS) whose main components are all fabricated using silicon microelectromechanical systems (MEMS) techniques is demonstrated for the first time. The ion source consists of a microengineered alignment bench containing a V-groove mounting for a nanospray capillary, an ion-extraction electrode, and a pneumatic nebulizer. The vacuum interface consists of two plates, each carrying a 50-μm-diameter capillary, that are selectively etched and bonded together to provide a differentially pumped internal cavity. The quadrupole filter consists of a microfabricated frame that provides mountings for stainless-steel rods measuring 650 μm in diameter and 30 mm in length. Two different quadrupoles are compared: a first-generation bonded silicon device and a second-generation silicon-on-glass device with a Brubaker prefilter. Differential pumping of a MEMS component is demonstrated for the first time, atmospheric pressure ionization and ion transfer into vacuum are characterized, ESI-MS operation is demonstrated, and spectra are presented for a variety of compounds.