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Are there any helpful websites for mass spec?
Mass Spec
- Thread starter sully677
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I'm sure there are, but do you have a specific question?
I'm just about to start studying and was going to hit MS too, so I could see if I have an answer for you. Would help me study too.
I'm just about to start studying and was going to hit MS too, so I could see if I have an answer for you. Would help me study too.
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One of the harder concepts. Wish I could remember a lot of it.
Just to chime in, it has a tendency to show up on the MCAT, and is important in many aspects of research. I didn't pay too much attention to it, and had to relearn all of it when beginning my chemistry research.
Good luck!
Just to chime in, it has a tendency to show up on the MCAT, and is important in many aspects of research. I didn't pay too much attention to it, and had to relearn all of it when beginning my chemistry research.
Good luck!
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Yeah, in that case I can't help out much.
I can give you a few basics though:
- It is a recording of the mass of molecules that are bombarded by a high energy (ionizing) beam. The now cations (because the high energy beam knocked off an additional electron) are then shuttled through a circular vacuum system and then are attracted to slit detector.
-The detector will be an indicator of cation size, with the largest on the outside and the smallest on the inside. Think about a semi driving around a corner versus a tiny ferrari. There is less force on the smaller car pushing it towards the outside than the little car, hence the order.
- Radical and Neutral molecules don't make it to the detector, because they can't round the corner, because of charge, nor stick to the detector if they do round the corner by some chance (not likely though).
- You can infer molecular formula from MS, and exact molecular formula from High res MS (because it's more accurate, so you can calculate exact molecular weight of compounds).
- Using Isotropic analysis you can see that Cl has a 3:1 ratio and Br has a 1:1 ratio, so if you get 2 peaks you ask yourself if it's 3:1 (then it's Cl) or 1:1 (Then it's Br). This is based on the naturally occurring isotopes in the environment, there is ~75% naturally occurring 35-Cl and ~25% 37-Cl (referring to isotopes), so that gives the 3:1 ration. Bromine is roughly 50/50, with ~50% 79-Br and ~50% 81-Br.
-So if you have Cl or Br in the compound it will have two peaks.
-And from all your previous lessons in OChem you know that molecules strive for stability, so compound that are more stable are more common, well this is definitely still the case with MS, the highest peak is your most stable compound or most likely fragmentation (this is called the Base peak).
- With the rest of the peaks it's important to think of the different fragmentation compounds possible.
So, with the basics in mind you basically just look at your printout and do the following:
Look at total MW, then subtract that from your base peak. This should give you the unit lost. So say the MW is 58 and the Base Peak (BP) is 43, you can subtract the BP to find out that Alpha cleavage occurred and you lost a methyl group (C = 12, Hx3 = 3, total = 15). This should give you good place to start. then to finish identifying your compound, unless you're using high resolution MS, you'll need to look at your IR, NMR, and CNMR.
Sorry for the long post, maybe you already knew all this, but it just helped me review some of the concepts too. So hopefully it helped some.
I can give you a few basics though:
- It is a recording of the mass of molecules that are bombarded by a high energy (ionizing) beam. The now cations (because the high energy beam knocked off an additional electron) are then shuttled through a circular vacuum system and then are attracted to slit detector.
-The detector will be an indicator of cation size, with the largest on the outside and the smallest on the inside. Think about a semi driving around a corner versus a tiny ferrari. There is less force on the smaller car pushing it towards the outside than the little car, hence the order.
- Radical and Neutral molecules don't make it to the detector, because they can't round the corner, because of charge, nor stick to the detector if they do round the corner by some chance (not likely though).
- You can infer molecular formula from MS, and exact molecular formula from High res MS (because it's more accurate, so you can calculate exact molecular weight of compounds).
- Using Isotropic analysis you can see that Cl has a 3:1 ratio and Br has a 1:1 ratio, so if you get 2 peaks you ask yourself if it's 3:1 (then it's Cl) or 1:1 (Then it's Br). This is based on the naturally occurring isotopes in the environment, there is ~75% naturally occurring 35-Cl and ~25% 37-Cl (referring to isotopes), so that gives the 3:1 ration. Bromine is roughly 50/50, with ~50% 79-Br and ~50% 81-Br.
-So if you have Cl or Br in the compound it will have two peaks.
-And from all your previous lessons in OChem you know that molecules strive for stability, so compound that are more stable are more common, well this is definitely still the case with MS, the highest peak is your most stable compound or most likely fragmentation (this is called the Base peak).
- With the rest of the peaks it's important to think of the different fragmentation compounds possible.
So, with the basics in mind you basically just look at your printout and do the following:
Look at total MW, then subtract that from your base peak. This should give you the unit lost. So say the MW is 58 and the Base Peak (BP) is 43, you can subtract the BP to find out that Alpha cleavage occurred and you lost a methyl group (C = 12, Hx3 = 3, total = 15). This should give you good place to start. then to finish identifying your compound, unless you're using high resolution MS, you'll need to look at your IR, NMR, and CNMR.
Sorry for the long post, maybe you already knew all this, but it just helped me review some of the concepts too. So hopefully it helped some.
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