Segmented Quadrupole — PCB Edition

Recently we’ve been working on the design and construction of a new instrument build centering around a quadrupole mass spectrometer as a detector for ion mobility spectromety. The primary motivation is to monitor the arival time distributions (ATDs) for specific ions without the duty cycles limitations of TOF system. In many ways this may concept may be counter-intuitive, however, though TOF systems are quite fast (operating into the kHz range), if they are used as sampling devices for drift tube IMS separations cycle times in that approach 10 kHz only allow sampling of the IMS domain every 100 microseconds. When placed into context of higher resolution IMS experiments such sampling rates are largely inadequate for capturing enough points across the ATD. While we surely have not solved this problem fully, the current build needs to shuttle the any ion packets efficiently towards the detector. Stated differently, any delay in getting ions to the detector aids contributions to peak widths from diffusion–this we want to minimize. Below are a few sketches of the target build in Solidworks and the newly arrived segmented quadrupoles. Key things to remember is that this design is not aimed at a resolving quadrupole but rather one focused on ion transmission. Also, the great technical notes at Ardara Technologies would suggest that a simple rectilinear quadrupole would be sufficient for ion trasport but we simply wanted to explore this possibility.

Building upon some of the ideas at the Rowland Institute we had some of the segments comprising the higher pressure quad manufactured along with the necessary coupling board. The coupler depicted corresponds to the one-half of the RF signal needed to power the setup. Stay tuned for the results on the implementation. For those interested in the actual files (still a work in progress) hop on over to github for the files.

Schematic of the segmentic PCB ion guide.
Top view of the segmented quad. Things to note include the 0.01″ teflon spacer between boards. The tabs are not ideally located (oversight on beta design) but in newer version this is corrected. The clamp is simply used to simulate the compression necessary to hold the setup together.
Side view of the assembly. Notice that the PCB routing does not produce a smooth surface, however, we expect the ion transmission characteristics to be largely unaffected by this manufacturing by-product.
Slotted coupling board illustrating the concept behind the assembly and electric signal connections.

Open Source IMS Initiative Update

 

Following up on previous post, we’ve finally released a major update to the Open Source IMS Initiative.  Appearing now in Hardware X we detail a new modular IMS design that is extremely flexible.  Three of our ASMS 2018 posters feature data from these system and the are proving an invaluable new tool to our research infrastucture.  Though the current systems are limited to lower temperature operation (i.e < 120 °C),  the designs are readily adapted to Rogers material which is quite robust well above 200 °C.  Another key adaptation making this design tractable is the new ion shutter design which uses 3 grids to create a set of well defined ion pulses.  Though the BN-gates are attractive in that the physical structure is in a single plane, their construction is an art.  Moreover, the fields established by the BN gates are also, by no means, fully planar.  With the new design we can achieve that smooth field in the region surrounding the ion gate and still get extremely small ion gate pulse widths (i.e < 20 μs).  If you are interested in some of the core details or have suggestions for improvement, come find us on github:  https://github.com/bhclowers/OS-IMS

 

PCB Tools and Gerber Viewer

Though seemingly outside the realm of chemistry, electronics lie at the heart of many experimental disciplines as all rely ability to make accurate and reproducible measurements.  An unfortunate byproduct of this requirements is often the reliance on outside sources–just look at your oscilloscope should there be any questions.  In an effort to minimize this reliance an maintain a solid knowledge base within the laboratory we often use the following tools for simple circuits:

Eagle — Great, free board editing and layout tool

Gerbv* — Simple, cross-platform gerber viewer

*for those working in OSX ♠hombrew♠ must be installed prior to installing gerbv. Beware, homebrew will change your life.