YOU CAN BUILD A MASS SPECTROMETER THAT SORTS ATOMS BY WEIGHT ON YOUR BENCH
A mass spectrometer that runs on a workbench and identifies atoms in a sample by weight.
by Ben Krasnow
ScienceWorkshop
- difficulty
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- a multi-weekend project
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- license not specified
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●●●●● · a multi-weekend project · license not specified · 0 stars · repo
WHAT YOU’LL NEED
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COMPAREE VERDICT
This is not a weekend project and it is not a project with files. It is a masterclass in analytical instrument design, filmed as Ben Krasnow builds a simple magnetic mass spectrometer based on a classic 1960s 'poor man's mass spectrometer' paper. The sample is ionised thermally, the ions are accelerated and bent by a magnetic field, and the bending radius depends on their mass: sweep the accelerating voltage and you sweep which mass reaches the detector, then measure the tiny ion current. In the video he measures the potassium in a dietary salt substitute. The hard parts are the vacuum, a stable ion source and a very low-noise current measurement. There is no parts list and no schematic; the video and the papers it cites are the documentation. This is for someone who wants to understand how a mass spectrometer works and has the bench skills and patience to build one from scratch.
IN THE REPO
GOOD TO KNOW
- —This is a filmed build walkthrough, not a documented project with files to download.
- —There is no repository, no parts list, no schematic and no step-by-step guide.
- —The video shows the physics, the ion source, the magnetic separation, the detector electronics and the resulting spectrum on camera.
- —To replicate this you watch the video repeatedly and source every part yourself.
- —The work is fully open — Ben explains everything — but there is nothing to click and buy.
- —No licence applies because there are no design files to licence.
Parts to buy
6 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Videos
Creator’s build video
The full build walkthrough, physics explanation and live spectrum on camera.
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Watch the video through once without taking notes (Understand the physics and the signal chain before you start sourcing parts.)
- 2.Map out the five subsystems(Vacuum chamber, thermal ion source, accelerating voltage and magnet, detector and current amplifier, sweep and display. Each one is a project.)
- 3.Start with the vacuum system and the ion source(This is the hardest part to get stable and it determines whether you will resolve anything. Test it on the bench before you build the chamber.)
KNOWN ISSUES
- There is no parts list. You are sourcing everything yourself from what you see in the video.
- The ion source has to be stable. A thermal-ionisation filament that drifts in temperature makes the peaks wander, so expect to spend time on the source before you see clean spectra.
- The ion current at the detector is tiny, so the current measurement needs a very low-noise amplifier or electrometer, careful shielding and good grounding.
- Vacuum leaks will stop you. Ions have to travel from the source to the detector without hitting gas molecules, so every seal and feedthrough matters and you need a proper high-vacuum pump and a way to measure the pressure.
- The geometry between the ion source, the magnetic field and the detector slit sets your resolution. Small misalignments smear adjacent masses together.
- This is not a project you finish in a month unless you already build vacuum instruments professionally.
Can I build this without a repository or BOM?
Yes, but only if you are comfortable working out circuits from the video and from the papers it cites (Dewdney's 1963 paper and a 1970 Scientific American Amateur Scientist column), and sourcing every part yourself. This is not a download-and-build project.
What is the hardest part?
Getting a stable ion beam and measuring a vanishingly small ion current. The vacuum has to be good enough for ions to travel without collisions, and the detector needs obsessive attention to noise and shielding.
How much does it cost?
The video does not give a build cost. The big items are a vacuum pump and chamber hardware, a magnet, a high-voltage supply and a sensitive current meter, and the total depends heavily on what you already own.
Is this actually useful or just a demonstration?
It produces real measurements: Ben uses it to detect the potassium in a dietary salt substitute. It is a teaching-grade instrument, not a commercial analyser.
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Discussion1
FROM THE COMPAREE TEAM
Ben measured the potassium in a dietary salt substitute with a magnetic mass spectrometer he built on his bench. If you built this, what would you point it at first?
Ben Krasnow
Ben Krasnow is an engineer and the creator of Applied Science, a YouTube channel where he builds scientific instruments, materials experiments and precision hardware on his bench. The channel is known for taking advanced lab techniques and showing how they work in a home workshop.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM1mo agoedited
Practical notes from our verification: there is no repository, no schematic and no BOM; this is a filmed build where you learn by watching and work out the circuits yourself. Despite how it is sometimes described, Ben's instrument is not a quadrupole: it is a simple magnetic mass spectrometer that ionizes the sample thermally and separates the ions by bending them in a magnetic field. The video description points to the sources he built on, Dewdney's 'Poor Man's Mass Spectrometer' paper from 1963 and a 1970 Scientific American Amateur Scientist column, and those are the closest thing to written documentation. Expect to deal with vacuum, an accelerating high voltage and a very small ion current at the detector. This is a long project unless you already build precision instruments. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.