Re: [DIYbio] Re: Do-it-yourself NMR spectroscopy

Detecting 1H(especially water) in NMR is the easy peasy thing because it is sooo abundant(99.98% 1H). People first detected water using NMR in the 1940s.50s? Other spin 1/2 nuclei however are not so abundant (C13 = ~1% and N15 = ~0.4%). What this means is that you either need a sample that is huge(liters) or pure and highly concentrated(> 20mM) or you need 15N 13C isotopes which are $$$$$$. Detecting these signals, say carbon splitting can be difficult for modern spectrometers(>=10 Tesla) on anything but very simple molecules not to mention water signal suppression as water will overtake your spectra, shiming to create an even magnetic field, and as people have said signal to noise.

The OpenNMR says they use a superconducting magnet which cannot run at room temperature(at least I don't know of any room temperature super conductors). Usually to make a material super conducting you need to drop the temperature down to < 10K using liquid helium with a liquid nitrogen barrier to prevent rapid evaporation of the helium. These liquids are not cheap. Also, when using electromagnets field inhomogeneities can become an issue. Then you need D2O($$$) for signal locking for frequency drifts. Many detection coils nowadays are also at cryo temps to reduce electronic noise.

It seems like a cool hobby but realistically it doesn't seem very plausible to create a spectrometer that can do much more then detect water DIY. There is a reason somewhat besides price gouging that modern spectrometers cost in the millions of $$$$.

During my Ph.D. I used NMR extensively(Varian and Bruker) and took care of the NMR spectrometers ((500MHz and 600Mhz Varian) usually NMR spectrometers are referred to by their 1H resonance frequency not their magnetic field strength(I don't know why?) so I don't know the Tesla) at University of Chicago for a bit so I know a little but I am by far no expert just an NMR user.

Josiah


On Thursday, March 20, 2014 7:58:38 AM UTC-7, Jonathan BISSON wrote:

spencer whyte <spence...@gmail.com> writes:

> Hey, another student here. I have been working on my own DIY NMR on a
> budget for a little while now.
>
> Nathan is right, when operating at low fields it is a constant fight
> against noise.
>
> The best article I have seen so far is this one:
>
> http://iopscience.iop.org/0957-0233/21/10/105902
>
> It is an absolute must read if you are interested in constructing your own
> NMR on a budget.
>
> All the best,
>
> Spencer Whyte
>
>
Hi,

You will need to take care of what you are looking for. Which kind of
samples do you want to analyze ?

The chemical shift dispersion is dependant of the field. So on
ultra-low-fields, you will not be able to distinguish different
compounds (at least not all their signals) and you will be overflooded
by higher-order effects and the influence of coupling constants (which
are everything but negligible at these fields).

I'm pretty impressed by the S/N quality of their spectrums, well ok they
used 0.5L of sample ;) but still, with such cheap amplifiers that's a
good result.

Their technology is pretty nice and can be improved a lot. Especially
decoupling the computer from the acquisition, you can use better cards
than arduinos and connect sdcards for storing acquisitions. Then you can
run your system completely in a faraday cage, avoid those main (50 or 60
Hz and their artifacts) and CFLs (ahh those crappy little emitting
things…)

If you need to develop a complete system you have these :
http://store.gadgetfactory.net/papilio-one-250k/
(This one is just an example, there is a lot of FPGA cards out there)
They will need a lot of development, but having an autonomous system is
priceless in these conditions and you will not be limited anymore by
limitations of an arduino.

Hmmm now I want to build one :p