Mass Spectrometry


Professor Dave here, I want to tell you
about mass spectrometry ok so when we do mass spectrometry what
we’re doing is we’re taking a sample and we are vaporizing it and then ionizing it and
then smashing it up into bits, and then we take those bits and we send them
through this tube and then they go through a curved section, where because
they have a formal charge of some kind they have a curved path with
which we can get data that will tell us something about the mass-to-charge ratio
of each of these bits. so m / z is the mass-to-charge ratio and if these have a
single charge, or you know, plus one charge then we can essentially think of
this as the molecular mass of each little bit, each little chunk of the
molecule so what ends up happening, what I’ve
drawn here is a sample spectrum. this is pentane so let’s say we have pentane,
now if we’re gonna ionize that and smash it up into a bit into bits what kind of bits are we going to get?
well let’s say we you know smashed off one of those carbons we’re going to get
this four carbon chunk or we could smash it up right here, we could get a
three-carbon chunk and a two-carbon chunk or right here, three and two so there’s all kinds of different chunks
that we can get of the molecule and those will have their molecular masses
represented right here and so for example right here, we’ve got,
this is 72 and so what this means is that some of
the parent molecules will be ionized and turn into our something called a radical
cation so this is a radical cation this is
essentially the mass of the parent molecule of the whole thing and so we
don’t see any data beyond that because there can’t be anything heavier in there than the whole molecule so this represents the entire molecule,
that’s the molecular mass of pentane and then what we can get is what this
data is telling us something about the chunks or the fragments that we can find
in a molecule, so over here at at around 57 this would probably correspond to if the
butyl, it would correspond to the butyl cation and so that’s if one carbon got smashed
off the molecule we’ve got this butyl cation, it’s
flying through, we collect the data we get a mass to charge ratio of 57 there’s going to be a good amount of
that, over here we’ve got 43 so 43 probably corresponds to the propyl
cation, so if we add up all the atomic masses we’re gonna get 43 for that so
that works there, we’ve got 29 right there and that could be the ethyl cation
and then we might get a good bit of the methyl cation which is going to be
around 15 now first of all the one thing we
want to talk about, what’s all this little extraneous other data well the thing is we’re going to have
some amount of compounds that have atoms of different isotopes so we might have some carbon 13 we might
have some carbon 14 we might have some hydrogen two or three
and so there might be some data that corresponds to fragments that have atoms
in them of different isotopes and so that might give us a mass to charge
ratio that’s slightly different, those will usually be smaller peaks because
by far the most abundant carbon is carbon 12, by far the most abundant
hydrogen is hydrogen 1 and so we’re not gonna see too much of that other
data but it is there and that’s why we see it, and then just to give you an idea of why this
is useful, once again maybe we are using this in conjunction with IR spectroscopy
or some other some other spectroscopic method to try to identify what this
molecule is and all we’re going to use this for is to, say we’re going to, if we
have a proposed structure for a compound we might compare it to a mass spectrum
because we’ll say, let’s say okay this is this is my molecule and I’ve got all
these parts here, and what we might say is, well if that’s the
structure we better expect to see that fragment right there and so all we do is we compare a
proposed structure to a mass spectrum and see if that mass spectrom
corroborates it another thing we could do is if
we know we have pentane but we don’t know which kind of pentane or are we are
looking at different structural isomers of the same empirical formula, just
looking at the way that it might feasibly break down into fragments, the mass spectrum will help us corroborate a particular structure so that’s the very basics about mass
spectrometry thanks for watching guys subscribe to my
channel for more tutorials and as always feel free to email me

79 thoughts on “Mass Spectrometry

  1. Is it also possible to break C-H bonds and see loose hydrogens on the spectrum? By the way, your videos are greatly appreciated, thanks Prof.

  2. how do i know the height of each peak? i mean the relative abundance or intensity. i need it to draw a spectrum of a given molecule

  3. A way that I found reasonable to understand it is with an analogy to chromatography, but instead of having a solvent, you have a magnetic field and instead of having a retardation factor, you'll have the mass/charge factor which determines the amount of specific broken and ionized products instead of distinct substances.. Is this right?

  4. Great video! I would've liked some comment on the m+1 peak though, since we can gather some info on # of carbons from the ratio of the M+ and M+1 peaks. Still don't totally get that, but I know I'm supposed to be able to tell number of carbons from it. haha Thanks again.

  5. is it possible that elements also gets seperated ie Hydrogen and Carbon, or just whole molecules will only gets ionized ie CH4?

  6. Prof. Dave, I'm taking Masters right now and we are self-learning these things. I'm thankful that you post videos on instrumentation. Perhaps you know how to teach us on method development? πŸ™‚

  7. is it right to say that
    " because the ions have a formal charge of some kind, they have a specific curved charge "
    ??

  8. I work for a university. I watch Professor Dave's videos because he explains this stuff better than my own faculty.

  9. Hi Dave, which machines are you using, and find most useful? Analytik Jena, Agilent, Bruker or value scientific? Keen to hear your thoughts on each .

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