Device Design and Construction
Description of Device
A cross-section of the full 3D printed IMS device is shown Fig. 4.1. In brief, the device consists of 3 regions: the source region (section (a), highlighted in orange), the ion injection region (section (b), highlighted in blue), and the drift region (section (c), highlighted in green). The source region consists of an 3D printed open outer cylinder with an inner diameter of 30 mm and a neutral blocking disk with an outer diameter of 15 mm and a thickness of 1.6 mm. Like the drift rings discussed in the following paragraph, this central disc is connected to the outer walls of the cylinder by 3 filaments, each 0.7 mm wide. A nanoESI tip is placed within the open end of the source region and for most experiments was located 5-15 mm distant from the neutral blocking disk.
The injection region is composed of a ring electrode and a stainless steel mesh held in contact with a ring electrode identical to the drift rings and is separated from
Fig. 4.1 Cross-section view of 3D printed IMS showing the source regions (a), injection region (b), and drift region (c). The injection waveform is shown in the bottom-left of the figure
Fig. 4.2 Top-down view of drift ring electrode design
the first electrode of the drift region by a 0.96 mm thick PLA spacer ring. A top-down view which highlights the design features of the drift ring electrodes is shown in Fig. 4.2.
The drift region consists of a series of 30 identical open rings with an inner diameter of 30 mm for a total drift length of 75.84 mm. Each drift ring has a central coaxial disc with an outer diameter of 15 mm. The central discs are connected to the outer rings by 3 filaments 0.7 mm wide. A stainless steel mesh is held flush with the opening of each end of the drift region. These meshes serve to limit electric field perturbations from the injection waveform and to shield the detector from image current arising due to approaching ion packets. A Faraday plate detector consisting of a copper disc was placed 1.6 mm distant from the final mesh.
All stainless steel meshes, including that used in the injection region, were purchased as sheets from E-Fab (Santa Clara, CA, USA). Each mesh is 80 ^m thick and contains 500 ^m wide hexagonal openings with 76 ^m webbing (69% open). The meshes were cut by hand to appropriate shapes using a normal pair of scissors.
Drift rings, stainless steel meshes, and the source electrode are all held in a 3D printed housing made of polylactide (PLA). The design of the housing is such that electrodes are held at defined spacing (0.96 mm) for an electrode pitch of 2.56 mm. The incorporation of spacers in the structure of the housing simplifies the construction of the device and reduces multiplicative errors from individual spacer height variations. The Faraday plate detector is separated from the terminal mesh of the drift region by a PLA spacer and is held in place by a screw-on conductive plastic piece. This piece is grounded to electrically shield the Faraday plate.
The rounded-rectangular portion of the electrode (see Fig. 4.2) is designed to slide into slots within the housing for a secure fit. The rectangular extension seen in the lower portion of the figure extends through the housing and has a small cylindrical opening, into which header pins are inserted for electrical connections to different components of the IMS. An image of a single ring electrode inserted into one side of the PLA/PHA housing is shown in the right image of Fig. 4.3.
Fig. 4.3 IMS assembly with electrical connections to electrodes through header insertion (left) and electrode housing showing integrated spacers and method of electrode insertion (right). Electrical connections made with header are indicated by the white arrow