Good news! We managed to observe an ion beam yesterday which was a good result and acquired a mass spectrum this is almost certainly a first for Hebden Bridge
Deep inside Hebbel end mill we succeeded in adding some protons (H+) to various test molecules (M) in the BR space to produce [M+H]+ ions! These charged particles were then flown through the mass spectrometer under high vacuum, they successfully navigated through the molybdenum quadrupoles surfed through the travelling wave ion guides and ended up hitting the dynode in the detector emitting electrons. These electrons were then accelerated towards a phosphor disk held at 9 kV this scintillating collision emitted photons which were then hovered up by the photomultiplier tube, there were some photoelectic special effects, lots of cascading secondary electrons et cetera… the ion current indirectly monitored was then amplified by the head amp to produce a 0-10 V output for analogue to digital conversion.
To cut a loooooooong story short we acquired a mass spectrum that did not look to bad. The front end of the mass spec needs some spring cleaning and we will have to tune up the mass scale and resolution but apart from that it looks pretty good - happy days!
Awesome! I’m still not quite sure what it does, but it sounds ace!
Lots of long words, @Giles! Hope you had an audience - give us more notice next time & hopefully there’ll be a better turn out.
Love the idea of photomultiplier tubes hoovering up photons
It certainly sounds good @9600, but some of us simply haven’t got a clue what it all means @Giles. Didn’t study much science at school . . . .
Hi All, it was not my intention to blind you with science!!! It was just a quick off the cuff statement with a very brief albeit confusing explanation of said aforementioned instruments innards!!! It was far from accurate and just for fun
A solution was sprayed from a syringe in the front of the mass spectrometer and a mass spectrum came out the back. A mass spectrum is like a bar graph from low mass to high mass (left to right) the amount of a substance disolved in the solution is proportional to the height of the bar for the corresponding mass or weight of that particular molecule.
Over the next few months I will do my best to explain the process of ionisation and how the mass analyser (quadrupole) works in the Quattro Premier. Please do not be put of by big words, it all depends on what you are interested in. There are many scientists that just view this instrumentation as a magic box that gives them answers, they just put their sample in one end and get an answer out and they do not need to know what happens in between.
It would be great if we could endevour to learn the applications, interpretation if mass spectra and also learn a bit more about the innards I would be only to happy to share this information and simplify the jargon.
I should have included a photo of the mass spectrum it would have saved 1000 words and would have been easier to visualise the concept. Next time I am in BR I will get a copy of HB BR 1st mass spectrum and publish it on the discourse with an explanation.
If you imagine a bar graph, there are many bars one for each mass and the height of the bars is proportional to the amount of the substance present in the solution, every substance has a different mass. Paracetamol for example has a nominal mass with a proton [M+H]+ of 152, cyclo dextrin 2034, polypropylene glycol 1080
From the periodic table we know that hydrogen (a proton) weight 1, carbon 12, oxygen 16, nitrogen 14 etc… the molecules that are detected have a certain number of carbons hydrogens oxygen depending on what they are. The mass spectrometer can help with the elucidation of the molecular structure.
I hope this helps
Yes, @Giles, that helps . . . a little. Look forward to seeing it for myself
It does help @Giles! Are they used for identifying unknown substances? Do you have to account for air as well?
Hi @Shirtboy James, the mass spec I have been talking about analyses liquid samples. Gas would only be an issue if it could be ionised, if the sample is highly volatile and can be heated to form a gas then yes it would be ionised. We can not see air though, we can observe the gases in air with the other mass spectrometer the Trio which I found in a skip!
With the liquid chromatography mass spectrometer (LC/MS) it is easiest to look at one substance at a time, ie one pure substance disolved in a pure solvent (could be water as the solvent). With the system we have (LC/MS/MS) there are two stages of mass spectrometry so we can acturally look at more than one substance at a time but lets keep it simple for the moment.
The solution is sprayed (nebulised or pneumatically assisted with nitrogen gas) through a needle that is held at high voltage typically 4000 V. The charge from the high voltage goes onto the droplets. This ionisation process is called electrospray and resulted in the Nobel prize for chemistry so it was a pretty important breakthrough.
The spray is sprayed into hot nitrogen gas (called desolvation gas) which causes the solvent to evaporate or de-solvates the substance from solution. Once all of the solvent has evaporated the charge is passed onto the substance that was disolved and produces an ion which is a charged molecule.
Once a substance is ionised it can be influenced by magnetic or electrostatic fields which can be used in the case of a mass spectrometer to seperate out the ions of different mass. As the mass spec scans the various voltages inside from low to high it detects low mass and then high mass ions.
I understand a bit better now. Thank you for the detailed response! I thought I was okay at physics, but this has blown my mind!
@Giles we’re now being followed on Twitter by BMSS: