Applied Science - 2019-11-30
How to build and operate a simple mass spectrometer. Please ask questions in the comments, as always. (I had to re-upload this video to fix the ending --I'm very sorry if your early comments were lost!) Scientific American article: https://www.scientificamerican.com/article/the-amateur-scientist-1970-07/ $7.99 is a good value for the entire back issue in plain PDF format, and an example of a publisher being reasonable. I'm happy to support this. Original Dewdney paper: https://sci-hub.tw/https://doi.org/10.1119/1.1969211 https://en.wikipedia.org/wiki/Isotopes_of_potassium https://en.wikipedia.org/wiki/Ionization_energy https://en.wikipedia.org/wiki/Thermal_ionization https://en.wikipedia.org/wiki/Gyroradius https://www.patreon.com/AppliedScience
I believe you are correct that the large peak is the 39 M/Z and the shoulder on the front of the peak is the 41 M/Z
I am a retired Field Engineer from one the worlds largest manufacturers of mass spectrometers. Your mass spec resolution of about 2 M/Z is very impressive.
you may increase your resolution by replacing the source 'side shields' with small magnets on either side (most of our sources utilized magnets in the source in this manner to increase the beam focus)
The small peak at a calculated M/Z of about 47 it is likely CO2 from an air leak.
In troubleshooting ms systems the CO2 peak was a ubiquitous signature of an air leak.
Building a GC or HPLC front end is a walk in the park compared to a mass spec. I
I can supply you with some components at 'cheap-to-free-prices' if you are interested.
@hedgeclipper418 the masscal is not that precise. So it could easily be 12C+16O+18O=46, the most common second mass of CO2. If the scan range went down to 44, you could test that hypothesis. My personal guess is double sodium, also 46. If it's leak CO2 then you would also see it with no sample on the filament.
@A A I love that "just".
@Jonathan Snow if it is a possible air leak as WilWinston suggested the main peaks that show up would be from Nitrogen. mass 47 could be NO2. ??
Thanks for chipping in, I found this very interesting, and your comment is enlightening, and supportive at the same time. I spent two decades in avionics, and I don't think I would've tackled such a project, even if I'd run into the reference, unless about twenty years ago or more. I was trying to think of what would've fit in that bump, and your experience gave valuable insight. I too am very impressed with the resolution, only among many other things.
@A A I think it's better to build an ESI source and that is not hard anyway.
I like how we all joked that you'd said "yet" in the tennis ball video when you mentioned mass spectrometers. And now you've gone and done it! Amazing. Been wanting to do this for years but the difficulty and tedium to constantly take it apart and put it back together always scared me off it. I think in a couple years I may end up building one now! Though I'm excited to see the follow up you mentioned. Quadrupole? Some RF magic? Lots of ways to make a mass spec, so I'm stoked to see what you choose. Have you picked up a copy of "building scientific apparatus"? there's a whole section on mass specs.
As to the 47mu peak, what about titanium? titanium dioxide is known to be a filler in salt products. It also has 1 common isotope at exactly the right spot, and then 2 much less common heavier isotopes and 2 lighter isotopes. Peak would look similair. If this can't resolve the potassium peaks I bet it can't resolve the titanium peaks well either so they get glomed together.
I knew he wasn’t joking! Considering the amount of amazing things this guy built, quite a few of them involving HV and HV (high vacuum and high voltage), a mass spectrometer is definitely within the realm of possibility.
I'm just imagining how the the sample injection could be done with a small capillary tube inserted into the rubber stopper next to the tungsten filament. Then you could continuously inject liquid analyte and have the filament just function as the electron impact element. And building quadrupole for it sounds awesome too!
@Zac Ragan The problem is the atmospheric pressure would likely push the sample in way to quickly, so it would have to be fitted into a reduced pressure container, which adds a whole other level of possible issues.
Excited box you are probably thinking of tungsten not titanium.
Irvin Coria I would have thought the assumption of it being well mixed is reasonable in this setting.
Yes!!! Have been looking forward to this video, and so appreciate the post-validation breakdown.
Previously on Applied Science: "I would have used a mass spectrometer, but I haven't built one yet". And here we are.
That's too good!!! Now I want a timestamped url link whatsit! lol LOVE this channel!
@Stefan Kawalec legend! :)
You are good. :-)
Measuring sodium might be a good way to check whether that second peak is just an echo. Sodium pretty much just has one naturally occurring isotope, so if you see a second peak that would confirm your theory of there being some kind of echo artifact.
@Wei Ni Hao There are too many for me to list here. The Nondestructive Testing Handbook: Volume 1 Leak Testing published by the American Society for Nondestructive Testing covers a majority of it.
@CafeBikeGirl Thank you very much!
All the pedantry aside, it's a good suggestion and I hope Ben noticed or at least thought of it.
Exactly.. I think that extra peak could be a type of resonant echo. One way that you could test it is by changing the diameter of your tube and see if that changes the location of the echo... Otherwise, it could just be that the potassium chloride/ water solution has a contaminate in it..
@KASA theory generally implies that it has been used to make predictions that have been tested and confirmed.
I wish there was a “I couldn’t love this more” button on YouTube.
Favorites! I think favoriting videos can affect the outcome/publicity a video gets!
You should change your name to ion Johnston. Surely that would boost your resume at the least.
Probably what Patreon can be used for..
Cool. Just don't build an anti-mass spectrometer and start the resonance cascade!
Let me finish the HEV suit first.
To rule out differences between forward and reverse scanning directions, you could use a sawtooth deflection voltage. This will remove the reverse direction almost completely.
@James Wyatt in this application it makes sense to use a transformer designed for audio. For the COTS audio amplifier, I recommend a battery powered Bluetooth speaker. I would use a signal generator app on my phone as the audio source.
Audio transformers may not have 425 volts of isolation between windings. The battery powered Bluetooth speaker conveniently provides meters of isolation between the signal source and the 400 volts.
It would be interesting to change AC frequency. I wonder if changing voltage can cause filament vibration.
@31337k good point. A vibrating filament will release ions faster.
If that isn't a problem, we don't have to worry about filament life. The time to release a sample is so short that filament reliability won't be a problem.
@hamjudo Note that Bluetooth audio is a bad choice for this job. Because it is a psychoacoustic compression of a limited precision digital sampling of the requested waveform, not a linear system of inductors, capacitors and resistors.
However, actual audio transformers designed to isolate mains voltage were common components in tube based audio equipment, so may still be obtainable. Another relevant component source would be the ferrite transformer cores used in switched mode power supplies. Winding a custom transformer with these cores and the related mains isolation materials should be fairly trivial for someone already building custom electron emitters.
@John DoDo Doe It is a pure sine wave. I would think that pure sine waves that aren't near either frequency extreme, would come through unchanged.
A problem with many audio compression strategies is that they turn sounds that are close to pure sine waves into pure sine waves.
The psychoacoustic aspect means that the algorithms are free to save bandwidth by throwing away phase information. Signals that look like white noise that has been passed through a bandpass filter should end up looking like unrelated white noise passed through an identical filter. The filter parameters are easily heard.
It can get all wonky when the signal can't easily be described like that.
5:16 “Nothing is an impossibility, so we try to do the best we can” - that is remarkably inspirational
Meh. It's too new-age-guru. Vague and almost nonsensical. Something you would here in an athletic locker room, or part of the outro of a documentary with a good soundtrack. Somethings really are impossible.
Going to another galaxy, colonizing an earth like planet, visiting a black hole, breaking c, digging to the earths core, etc. These things will forever remain intangible but by pursuing them we make life around the sun an increasingly satisfying adventure.
@Applied Science Talk to the guy who runs the Youtube channel Thought Emporium, he makes tons of scientific equipment from scratch on the cheap. He created a cheap Gel Electrophoresis and doc for it and I know that it's not a chromatograph but I bet if the two of you start talking about it you could create one in under a month. He has more of a focus on Biology though but Im sure he could make use of a Chromatography station if he had one. Same goes for a mass spectrometer now that I think of it lol. Speaking of it, can we see what shows up when you run a bare tungsten electrode in it without anything else to see if something about those parts is putting extra ions into the system to cause the smaller bump? Something tells me that Scientific American never thought that anyone would ever actually try to build one of these mass spectrometers. I hope with help and ideas from everyone we can get it working better. I was thinking about covering the end of the rubber stopper with something in an attempt to lower the off gassing but I don't know what would be better.
Keep up the unintentionally awesome inspiration and keep making awesome things!
here's a link to the video on his Gel Electrophoresis video to make things easier if you don't already know who I'm talking about.
https://www.youtube.com/watch?v=sSKls2kNC4U
He probably meant that you cant create perfect vacuum anyway, so he just tried to produce as good vacuum as possible :D
Miroslav Kašpar yes, as he mentioned above. I did understand the original intent, I was just also implying that it could be interpreted as an inspirational message.
lol.. 'nothing' meaning absolute zero-- that's what he meant
Here is an interesting thought that crossed my mind watching Ben comparing his results with the ones in these older papers:
In recent years, the issue of positive outcome bias got more and more attention in the scientific world. Positive outcome bias means, that if a hypothesis is written and scientific tests are conducted to either confirm or dismiss this hypothesis, researchers are more likely to publish their findings, if the outcome is positive, meaning the hypothesis was confirmed. While this seems perfectly reasonable especially from a humane point of view (we like to be considered smart, especially when being smart is part of our job), it is kind of un-scientific to filter your publication efforts based on your personal preferences. Furthermore, publishing dismissive experiments would help prevent other researchers from wasting their time trying to proof the same false hypothesis. This would raise the global scientific efficiency, boosting the progression of mankin… oook I got taken away there a little bit…
Writing a classical research paper, you think that the work you are creating will be exclusively read by other scientists that generally work in a similar field as you are (excluding youtubers 56 years in the future^^). This puts a certain psychological pressure on you because if you write about your mistakes or that your initial hypothesis is wrong, the readers could judge you in a professional/snooty kind of way – like a teacher giving you a hard time for not doing your homework correctly.
Seeing Ben talking so freely (and passionate) about his positive and negative finding during the building of this spectrometer, even questioning himself after he managed to produce readings similar to those in the papers… I think it's great and I barely find something like this in published research. Besides Ben being a total badass as always, maybe one reason for this is that his videos are made for, and will be watched by, basically everyone. Taking away the pressure of a strictly professional reader base may be helpful in tackling things like positive outcome bias. Of course I have no idea on how to implement that in a broader scientific scale. It's just a thought.
@CafeBikeGirl (Laugh!) So true!
There is a lot of misunderstanding about what science is and is not. Scientists have to get out of the ivory towers and laboratories (even though they're usually our comfort zone) and start letting people know what it's really like (and that it can be very hard and draining work, even though we might not be doing very physical activities).
For those that don't know - a hypothesis is in essence a question you can ask and get an answer through research and experimentation, with either a "yes" (supported) or "No" (disproved) answer. A theory is a hypothesis that has been repeatedly tested without being disproved, to the point that it is generally accepted as valid - and provides a good (and generally accepted) explanation for the 'phenomenon' being investigated. (There are non-scientific meanings to these terms which are largely based on people trying to claim some sort of 'scientific authority' but which are incorrect - like 'theory' being misused for 'an idea'.)
It's perfectly acceptable to say "I have an idea about that!" or "I don't know!" Indeed, "I don't know - let's find out!" is the beginning of science!
Science is also inherently materialistic, but this is in itself a 'thought-tool': it helps to guide our thinking and experimentation so we find out more about reality. For the unaware, many scientists are deeply religious, but they don't like to talk about it and know that mixing science and religion can be... wrong and dangerous.
There is a philosophy of science (a set of thought-tools) that goes way over people's heads... for instance regarding forms of reasoning. I've regularly encountered people who insist that deductive (general to specific) reasoning is the only valid form, and that inductive (specific to general) is faulty - forgetting that sampling strategies make use of the second form. Most of the general public may have heard the third common form - adductive reasoning ("which theory or idea most accurately fits the data?") especially if they ever watched the Star Trek original series ("Spock" said it more than once as I remember), and it also can be quite valid and used in research. I know I've used it at times.
I hope that this nutshell explanation will help the lurkers - the readers of our comments!
I'll get off my soapbox now! (GRIN!) I live in an area full of rabid anti-science people who don't have a clue about the subject, and who often try to tell me what science is and is not - so I try to explain these things wherever and whenever possible! Sometimes if you're careful and thorough, you can help them to understand that you (and others like you) are NOT "the enemy!!!".
@salec (ROFLMAO!!!) I LIKE that analogy!!!
Very true. You get quick positive results, you'd better look to your methodology!
@codemakeshare That is very true -- "We tried X and could not get Y" does not carry much weight precisely because there are a million reasons why things don't work in practice. (And which are left unsaid even in good recipes -- relying on the experience of the practitioner.) A real proof that X and Y are independent factors -- a proof which excludes all possibilities -- that's a heroic thing, and a very different species of a "negative result."
@How Does it Really Work - Indeed. The usual cases where this is done thoroughly (the "why our hypothesis is probably wrong" investigation) is when someone reports on extraordinary findings. E.g. the "faster than light neutrinos" come to mind, that were followed by a rigorous search for other reasons that wouldn't break physics. I think it was a problem with a fibre-optic cable in the end... Disappointingly, our current understanding of physics remained valid after all... :)
As a former graduate student, this topic has been on my mind a lot.
I completely agree, that there is some insane value in being able to publish "failed" experiments in the sense that it would potentially save other researchers a lot of valuable time and effort.
However, there are several problems with that which I believe are at least partially the reason why there is no such thing as a journal of failed experiments.
First of all, as you already remarked, there is little prestige and glory in having done something that didn't work out so. Since writing and refereeing papers takes quite a bit of time, people will rather spend that time on getting results out there which will further their career.
Then there is the question should this journal be free to publish or should there be some kind of editorial work and/or peer-review involved? Again, this costs time and money that people would rather spend on getting positive results out.
Another issue is, if you have a failed experiment, who says that the experiment really doesn't work? Maybe you're overlooking something or maybe you're just not good enough to make it work. Just like positive results need to be independently verified to count, the same could be true for negative results. Publishing that something doesn't work when in reality it was a simple error on your side might mean that other people who might end up getting it to work will never even try.
And finally, while there is certainly a lot to be learned from having a good, solid hypothesis disproven by experimental results, who is to determine whether a hypothesis was even worthwhile to test from the start? I'm sure once you publish something that failed, some people will tell you that you could/should have known from the start that this wasn't going to work because of xyz. It would be difficult to avoid clogging up the system with people publishing all sorts of nonsense that was doomed to fail from the start and there is very little to be learned from those attempts.
It is definitely possible to publish "negative" results in the sense that if you have experimental evidence that flies in the face of established science, you can definitely publish that in the most prestigious journals and you will become famous for it. If you were to set out and confirm the theory of relativity which says that nothing can move faster than light and you accidentally end up showing that something can, you'll definitely get to publish that even though you "failed" to demonstrate what you originally wanted to demonstrate. The example is a bit contrived but you get the idea. Unfortunately, not every failed experiment meets those criteria.
"I'm going to show you how to build a mass spectrometer in the home shop."
[*Proceeds to produce a turbomolecular vacuum pump from yard sale junk pile.*]
You are amazing... I'm a service engineer and have worker with several mass systems from Agilent, thermo, Shimadzu... but to see some one building a mass unit... thats astonishing
That Tek scope alone is worth more than a BMW...
As someone who has spend some time around mass spectrometers I have to say the idea of someone rigging up a DIY mass spectrometer at home is crazy to me. Really impressive work!
However, on the theory side, a couple of points in this video were explained rather incorrectly. Mass spectrometry generally does not work by breaking up molecules into individual atoms and then determining the ratio between the individual elements present in the sample. This type of analysis is called elemental analysis and it's done in a very different way, not with a mass spectrometer.
For a molecule like bipyridine (as is shown in the video) you'd get a main peak around m/z (mass over charge) of 156 (or 157 for the +1 proton mass) depending on your setup and conditions. You might also find some peaks at lower m/z for fragments or more highly charged ions (e.g. the +2 proton mass).
Here's an example from NIST:
https://webbook.nist.gov/cgi/cbook.cgi?ID=C553264&Mask=200
What exactly you get out depends a lot on the machine, the operating parameters and the sample preparation. However, you will almost certainly not get something like C:H:N of 5:4:1. I've never seen any mass spectrometer that works that way.
EDIT: as some people have pointed out, with a very harsh ionization method like ICP (inductively coupled plasma) or thermal ionization you can indeed break up the sample into atoms. I was looking at this from a background of comparatively soft ionization methods like ESI (electrospray ionization), MALDI (matrix-assisted laser desorption ionization) and EI (electron ionization) which generally do not rip molecules apart into their individual atoms.
Also C14 does not turn into stable C12 by ejecting neutrons. Instead, it undergoes beta decay and becomes stable N14.
Regarding the "mystery signal" and the separation of potassium isotopes, I haven't checked the math but I can believe that the K41 signal is hidden in the "shoulder" of the main peak for K39. However, I do still think that the scientific american and John Dewdney were right in their analysis. I would be surprised if they hadn't calculated the masses of the individual peaks to verify their analysis.
If you look at their original graphs, the main peak may be slightly asymmetric but it's not nearly as asymmetric as in this video. So instead of the K41 peak hiding by not being fully resolved I rather think that their machines simply had better resolution and were actually capable of distinguishing between K39 and K41 more clearly.
If you want to compare the ratios of two signals in your mass spectrum like this you don't compare the peak height but rather the area under the peak. So the ratio of the peaks might very well turn out to be about 14:1 and not 6:1.
He have super-hard ionization. Dont compare thermal ionization to comon soft techniques used for organic molecules (ESI, MALDI, APCI, APPI...). So he might fragment his molecule to single atoms. Its similar technique as Induction coupled plasma mass spectrometer (ICP-MS) It can tell you same information as elemental analysis, eg. atom ration in your sample. I agree with other points you mentioned.
@Matt Verey like, plotting on paper and weighing it? :D
With greatest respect to your up to date knowledge, I am afraid that you are just not old enough...
My first encounter with a mass spec was in 1983. It was with a two tonne monster that was built in the sixties and had recently been retired to a university physics department. The ionisation chamber was not very much more sophisticated than the one in this DIY project it did have an airlock to introduce new sample preparations but this was because it took a couple of huge, loud pumps over an hour to evacuate the 2 metre long 90 degree curve which flared out to over half a metre wide at the detectors - a long line of electrodes that worked a bit like cascade photodiodes but for fast, heavy ions. It was covered in enormous electromagnets, of course, though they were actually only about as powerful as those in the video, I believe - less than 1T anyway (i remember this because that was a sort of break point at the time where more field strength started costing hundreds of times more. It was around this time that Culham Labs were building the first magnetic containments for nuclear fusion nearby, with a budget of millions.
The mass spec did have an ion accelerator - like a cathode ray tube - to improve precision and detection sensitivity, so it needed a much longer flight path than shown here.
The machine could principly discriminate C, N O and F and their various isotopes, but not H (far too light) and could be tuned to pick up some heavier metal ions with less accuracy. The information that the mass spec could provide was pretty limited but at the time it was much faster and more accurate than comparable chemical techniques. It could be used for quick, very approximate carbon dating or to help validate x-ray crystallography and odd bits of stoichiometric chemistry. One interesting project was to map out regional minor variations in relative isotope concentrations of N, O, C etc so that people could be placed with respect to where they grew up from just bone and tooth samples (intended for archeological research bu the forensic scientists got interested too.)
Another brand new idea was nuclear magnetic resonance, which at the time could only detect hydrogen ions. But it could detect them within an amorphous (very pure) organic molecule liquid AND hint at their connections within the molecule by the slight differences in the magnetic resonance. It was believed by some in the physics department that putting this together with mass spec and x-ray crystallography, they could finally usurp and swallow up the chemistry department for good.
@Ben Williams Thank you for the fascinating account!
I have nothing but the highest respect for the people who worked the early days of all the techniques that we commonly use these days like MS and NMR. We do have some of those ancient MS monsters around where I currently work but I have never touched them myself. They're mostly used for determining isotope ratios in radioactive samples. Rather impressive looking machines indeed.
My own work with mass specs concerned mostly much newer ESI Q-TOF type machines which were specifically rigged for higher masses so we could detect entire antibodies and antibody fragments. I've also tried to do some MALDI MS which was pretty cool to do but sadly the samples turned out to be too inhomogeneous for a meaningful interpretation of the data.
I've also done the occasional routine GC-MS analysis with an EI detector and routine analysis of transition metal complexes I synthesized using a fairly standard ESI machine.
The mapping of different isotope patterns to different regions makes sense to me but I'm still a bit baffled by the idea of determining elemental composition of an (organic) chemical by MS since I've never seen that anywhere.
How do you completely atomize the sample? Would you use ICP for that? Do you use any internal standards with that to quantify the different elements?
@Miroslav Kašpar Yeah, you could be right. I am indeed used to ESI, MALDI, EI... that sort of stuff. I figured a bit later after I wrote this comment that something like ICP might do the trick. But does thermal ionization really rip organic molecules like bipyridine apart into individual atoms? I could see that work for inorganic samples like KCl but I would not have expected that for organic molecules.
I would love to build one of these! Awesome video! The clear PVC tubing has lots of phthalate plasticizer oil in it which is relatively low molecular weight and would volatilize easily under such low pressure. The black rubber has no plasticizer and is highly crosslinked to to point where it is essentially one giant molecule
@chichi Huh? You can make rubber without seperate plasticiser molecules easily. The 'plasticiser' would be part of the rubber polymer.
And even giant molecules can be 'soft'.
@chichi Not necessarily rigid like a rock. If the monomer is a long chain and lightly cross-linked there will be enough freedom for the long chains to slip past one another and remain flexible.
@Emily Chb Of course you can have them without oil-like plasticizers. What I am saying that you have to be aware of what flexible material you are using because some of them definitely contain oil-like plasticizers. Conventional PVC tubing definitely does.
@chichi The rubber plug is probably isoprene or chloroprene, it's an elastomer. You can assume it to be almost fully crosslinked, i.e. monomers connected end to end to end to end in very very long chain. It's not actually a single molecule, but for all intents and purposes it might as well be, i.e. if the whole item was one such molecule, it would still have the same physical and chemical properties as a number of such sufficiently long chain molecules of thousands of monomers. The reason it remains flexible - while being a solid - is because this molecule is coiled up like a spring, and can uncoil itself to allow movement, without breaking, and without additives. Obviously not every such plug may be very suitable for vacuum, it might contain any number of shit in it, but it doesn't have to contain any volatile compounds, and if it does, chances are it's just a small residue and the first time you pull the vacuum, enough gets out that it doesn't end up mattering. Carbon Black pigment obviously doesn't become volatile for example.
Flexible PVC is actually mixture or suspension of sorts. The base material is a hard brittle plastic (which also has some other unfortunate properties, like, it actually is unstable and degrades super easily under a number of conditions), that is mixed with a liquid solvent, the plasticiser. There's an almost similar amount of plasticiser to the base material, and by the time you get a bunch of it out, the item becomes unusable, shrinks and falls apart. The solvent is supposed to be "non-volatile" under normal conditions, but i mean, have you seen what happens to PVC after some years, it obviously manages to escape, and obviously if you raise the temperature or draw a vacuum, you imagine what it does.
SA did an Amateur Scientist gas chromatograph "The Amateur Scientist
How to construct a gas chromatograph that can measure one part in a million
By C. L. Stong" September 1967
I was festinated by your presentation.
That’s awesome. I really need to go back through these Amateur Scientist articles, seems like they’ve got some sweet projects I could work on.
@Matt Shilling Hi Matt, I remember one of these articles that measured 'proton precession', the basis for today's MRI medical scans. My friend performed that experiment while I built a binary adder out of WW2 surplus relays, switches and pilot lights.
Also, "How to Build a Gas Chromatograph and Use It to Separate the Components of Mixtures", Stong, C. L., June, 1966.
You can buy gas sensors for under 20 bucks like the TGS-813 for example. Making a chromatographic column for gases is also fairly simple, just take some plastic tubing and fill it with sillica or even more ghetto and oldschool, bentonite clay from kitty litter. Flow a carrier gas through it, which can just be air from a cheap aquarium pump and inject your sample in there. The real problem in GCMS and LCMS is interfacing it with the MS, since the MS operates under high vacuum and your LC or GC operated in solvents or gases. In LCMS it commonly get's nebulized and shot past a tiny ESI pipe which goes to the MS, and because that's under vacuum, it sucks some of the spray into the MS while the majority just goes to waste. Maintaining vacuum this way requires a good pump.
i'd really like to see that glass diffusion pump working
Razer blade slits - classical DIY solution in optics... love it!
about the thickness of a razor blade, made from razor blades
"It's your comments that keep me going!!" Humble as always and excelent video!
With the right foresight with designing the vacuum line, its easy to use a diff pump where you need to frequently release vacuum. If you put a stopcock between the diff pump and the working line then you can close off the pump to the line, release the vacuum, and keep the diff pump refluxing. This way you can do whatever work you need and then reopen to the diff pump and it should pull down within minutes. You can keep a diff pump refluxing 24/7-365 as long as youre not pulling shit into it and keep it under vacuum (if you heat the oil under atmosphere it will char). Mine has been running for ~3 years continuously with no maintenance (though the roughing pump sees regular oil changes). Cold trapping also helps, but I have cheap and abundant LN2 so thats probably not worthwhile. Never used a turbomolecular pump so I cant comment on whether this is "better" or not, it's just what I have access to
Not sure if this is already known to you, but thought I'd chime in as a chemist who works on highvacuum lines frequently :)
I'm also a bit surprised that you had such large issues with tubing. I am able to maintain 1x10-6 torr with tygon tubing segments (rest connected with ground glass or o-rings). Definitely out to low millitorr you should be able to use clamped tubing (most schlenk lines in chemistry labs feature tubing similar to what you used, and 50mtorr is achievable on a good line--and that is pump limiting not leak limiting)
He should be able to hit -5 torr with that turbomolecular pump in about <5 min and reach an ultimate vacuum of -7, cheap roughing pump oil often has a vapor pressure of -5 torr so once it gets a little contaminated with solvents and water the system will peak out in the mid -4s assuming there isn't massive outgassing or leakage on the high vacuum side.
@CafeBikeGirl diffusion pumps are much higher volume though than turbo pumps per size. I have seen videos where the gauge plummets like a rock when they open up the diffusion pump and that is on a much larger chamber than that little pipe. Problem is that out-gassing is not free flowing gas so it takes time. To get lower he would also have to do a bake out to get rid of humidity.
No doubt that a bake out will help clean out all the crud in the system from initial assembly and make sure he's not getting stray signals from stuff outgassing but it's a molecular flow system, he's not going to get any more flow than what that KF25 connector allows which is going to be something like 30 or 40 liters per second. The pump he's using appears to be comparable to 140 l/s pump (for N2) Even then the analyzer portion is not going to flow any more than the ~1/2" T-fittings allow. Unfortunately his sample delivery isn't going to support doing a bake out during a measurement run but he should be able to squeeze out another order of magnitude on the vacuum with a little effort. My real point was that for $20-40 he could significantly reduce a potential source of gas load, and to your point if he hasn't done a system bake out yet that could reduce it some more without adding complexity. Backfilling with nitrogen would be a big help but he would need to add a valve for that (preferably two) and be very careful not to shock the turbo. These things would get him more working time with his sample.
@CafeBikeGirl & @excited box I truly enjoy your discussion above, as well as some other interesting notes above. I believe I can even follow, though it's 'not quite' my area of expertise. Of course, thanks to @applied science for an excellent video and a beautiful build!
Did you run a clean filament without any sample? As a control?
This is the best suggestion in the entire thread.
I built a Liquid Dye Pulse Laser based on an Amateur Scientist article in about 1970. As far as I'm concerned, you are the New Amateur Scientist!
Richard Burgan Hi, can you shed some light to us how you built the laser? Amazing thing.
.
@Peter Kuan The article is in February 1970 Scientific American. C. L. Strongs column "The Amateur Scientist". It might be hard to obtain the quartz glass parts that were available as a kit for a while right after the article's publication.
@Peter Kuan You can go to Sam's laser FAQ to learn more about them, and there is Yun Sothory's excellent website about scratch made lasers out of easy to get materials, with his instructions i made my first flash lamp pumped dye laser. You can also make a relatively easier but much less powerful dye laser by first making a nitrogen TEA laser and then pumping the dye with it, just be careful tho this pulsed lasers look cute and inoffensive but will blow a hole right thorough your retina quite easily.
https://www.repairfaq.org/sam/lasersam.htm
http://laserkids.sourceforge.net/
'It's been days... or hours.'
Lol, gotta love projects like that.
Amazing work! Judging from the size of your turbo pump the level of vacuum is only that pump is able to keep well ahead of the leaks and outgassing! Copper outgasses a lot (oxygen free copper is better), aluminium brass or 304 stainless steel would be a lot better! The solder is not that much a worry but the flux is.
I used to work on this stuff........god 35 years ago!!
Yea, I'm sure his pumping speed is whatever a KF25 will provide at that temperature and the little copper T-connections on the analyzer. I'm curious how he obtained one that big for "home use" in operational condition.
Did you do a dry run with nothing on the filament to see if anything is emitted from it?
Excellent suggestion.
Measuring background noise should be a part of any mass spectrometer measurement so hopefully he did, although it seems like he's using the potassium as his known standard so maybe he didn't get that far before releasing a video.
"but anyway, back to this ion gun"
It would've been nice to see another graph with a different compound to see if the same mirroring effect existed. That would probably be the strongest evidence.
As another commenter mentioned, it could just be another ion (such as Ti) present. So if another graph presented a peak at 104V, then it may not be mirroring, but another ion. Whereas if the position were slightly different, it could be the mirroring you mentioned. If you could come up with a compound which would present a more unique double hump of two distinct peaks, then I imagine it would be the strongest candidate. But, then again, I don't offhand know of any solution you can make with two dissimilarly weighted elements (but I'm not a chemist).
@Vallecaucanisimo I believe it was around 47, which would make it titanium
You need the area, not the peak heights -maybe you are already doing that. Calibrate the spectrum axis with several know peaks.
Depending upon the shape of the peaks, this isn't strictly necessary; but you are correct -- it is more proper to use the peak integral.
Have you done a reference run without sample? Of course you might have. Its truly inspiring that you built a mass spectrometer. I understood lot of things fundamentally from your video. Thanks a lot.
Mix some calcium to the sample. Ca has an atomic weight of 40, so it should make a nice clear peak between the potassium peaks which should show clearly whether those are K peaks or not.
7:24 !!!!! Don't boil the oil!! I felt a great disturbance in the vacuum, as if millions of diff pumps suddenly cried out in terror and were suddenly silenced.
The diff pump oil should just have some slight movement during operation.
IT'S A TRAP.
I like watching every minute of this video.
Brilliant! Thank you. Finally I understand how these work.
I believe the peak you see at 104 V which calculates to 47 amu is Titanium that may be allowed into the filament.
alloyed got changed to Allowed, but I think everyone understood what I meant...
ElectronAsh I believe you solved it
or titanium dioxide in the salt as color/anti caking agent
@ElectronAsh I had to look that up and I was surprised I hadn't heard of it before. Good stuff!
@JackFou Well, you do need to be sure to prevent side-fumbling. lol ;)
the prisma shown is the image of pinkfloyd album :)
Talk to the guy who runs the Youtube Channel Thought Emporium, he makes tons of cheap scientific equipment from scratch!
The second spike looks almost like a second order diffraction maximum. You have a slit (two, in fact) in the device and you're pushing particles through it. There's going to be diffraction pattern of some kind... the question is, would that effect be big enough to be detected in this way? Or is that just shown as "blurry spikes"?
Based on my calculations, a 39 amu, 1 elementary charge ion gains a velocity of about 24,969 m/s over an electric field of 126 volts (and it will have energy of 126 electronvolts).
At that speed, a particle with mass of 39 amu will have a deBroglie wavelength of approximately 4.1e-13 metres.
You mentioned that the width of the slit is about 3-4 thousandths of an inch, which comes to about 0.1 millimetres. Since the disparity between the gap width and the wavelength is so large, I don't think there should actually be a lot of diffraction, but still, the diffraction angle can be calculated. With the above wavelength, the first order diffraction angle would be 2.35e-7 degrees.
Estimating the length of travel for the ions as about 0.1 metres from emitter to detector, the actual distance between diffraction spikes should be in the order of 4.1e-10 metres, or about 0.41 nm.
That seems like too small a difference, so this is likely not the correct answer. But it would be really cool if it actually was that! It might be worth doing the math on how this diffraction would affect particle path and what voltage would result in the diffracted particles hitting the detector. The assumption of a constant radius of curvature would only apply if the beam is very tight, unless I'm mistaken. If the angle of the particles arriving to the magnetic field varies, then different velocities (that is, different emitter voltage) can cause them to hit the detector.
Although simpler explanation is probably contamination, like another commenter said, possibly titanium from the filament used to heat up the sample.
Also, are you getting a spike for chlorine? It should be at about 131 volts, by my calculations; that is the voltage that gives chlorine ions the velocity at which they have a matching curvature with potassium ions at 126 volts, so they should be hitting the detector at about that voltage range.
@CafeBikeGirl For leak detection?
@Jurjen Bos Not likely to get molecule fractions from a salt…
While that would be cool, the answer is probably more mundane: The AC used to power the bulb can't really be ignored - the DC bias causes it to be ground referenced, and thus the voltage between the sample and sensor has the additional component of the AC used to power the bulb, which is loaded and thus has a phase difference with the AC used to vary the bias, and the two interfere, giving two peaks.
The diagram doesn't seem to actually take that into account, and just measures the voltage of the other transformer plus the DC.
It's not a small difference- 9v for the diagram and probably 18v for him (center tapped Vs side tapped)
I honestly don't think that is the case given the width of the slit is orders of magnitude larger than the de Broglie wavelength of K+.
@Ian Oliver leak measurement but yes most people use it for detection.
That oil diffusion pump looks awesome!! I'd love to see a project like making your own neon sign, using it!
This was way over my head, nonetheless, I found it interesting. Thanks.
So THIS is what Gordon Freeman sounds like!
Maybe 47 amu peak is from titanium from razor blades?
@Reed Petersen regarding the titanium once ions struck the razor blade I believe they would be neutralized and either quickly adsorbed on the inner walls or removed through the turbomolecular pump which should have plenty of compression ratio keep the concentration low. Nothing should be eroding the tin, copper, or brass as far as a know and his vacuum level isn't high enough for them to be doing much. I would think oxides or contamination on those surfaces would be worse since they aren't the cleanest of metals. The rubber would likely be off-gassing compounds with much higher masses that I doubt would be within his measurement range unless they were being cracked by the ion source, my guess is they're probably just contributing to system pressure. I'm curious about the flux in the solder, that might take many hours of pumping to fully out-gas. Either way I hope he makes a video on tracking down what this peak is, especially since it is displayed in the other two papers.
The titanium hypothesis has the hole that 47Ti is not the most abundant of Ti isotopes. 48Ti is the most abundant isotope (74%) and 46Ti and 47Ti are about 8% of Ti and 49Ti and 50Ti are about 5% abundant. So if Ti was the contaminant in the spectrum you'd expect to see a large 48 peak and smaller peaks on both sides of it. However, what he sees is what appears to be a peak with one satellite.
Well thinking about some other substances we know will be in the system ammonium chloride solder flux is 53 AMU so that is too big, carbon dioxide is 44, Calcium is 40, has an isotope of 41 and might be a trace source of contamination if his salt substitute is made in factory that makes other dietary supplements?
I'm sure he already looked at a lot of other mass to charge ratios to find anything that coincides and the closest thing I can come up with is if the dietary supplement contained trace amounts of calcium which might also be handled in the same facility, but he would have to have an error of 1 amu somewhere. There are all kinds of phenomenon in electron optics that can cause a misaligned beam to strike the detector plate, it is interesting though that it appears to be repeatable with the design.
@CafeBikeGirl Calcium silicate is a common anti-caking agent, but NoSalt already lists potassium bitartrate in it's ingredients. (Potassium bitartrate is sometimes used as an anti-caking agent.)
You had me at "DIY mass spectrometer".
Love this channel! Can't wait for the DIY nuclear reactor so I can finally retire my solar panels :-)
I need to see a video on that glass oil diffusion pump! How cool!
7:15 nice bong!
This is something I've always wanted to see! Thank you very, very much!
This was absolutely pretty smart!
And yes I find it interesting, and that's an.understatement! Wauw! I hope to see more of this because I am sure I could watch this for hours and hours, best all in one go!
Awesome video ! Are you also ionizing the tungsten in the filament with this mass spectrometer ?
To lower input capacity of your transimpedance amplifier and photodiode there is a technique called bootstrapping, where you put another opamp in a buffer mode over photodiode cancelling its capacity. We even used it in exomars spectrometer
How well does that work for very small signals? just wondering.
Your videos are always interesting even though the science is over my head.
Tech Ingredients - 2019-11-30
This was very well done and very enjoyable to watch. You have to be near the top of the list of people that will never, ever, ever give up! Cheers
Corl Franco - 2019-12-03
loosing his sanity for us
Philip Canete - 2019-12-23
Well this makes sense! I see the many similarities between your channels
SV Chineel, Junk-Rigged Schooner Sailing - 2020-02-22
Hi! :)