Choosing a Benchtop NMR? Here are 4 Questions to Ask Yourself
Interested in choosing the right benchtop NMR for your lab?
Chris is here to help.
Why are you looking for a benchtop NMR? You might be a chemistry professor who teaches NMR, a synthetic chemist who needs to determine or confirm a molecular structure, or maybe you use NMR in R&D. You’re looking for the right benchtop NMR for your work and maybe need a little help so you won’t have any regrets.
You are in the right place! Hi, I’m Chris Tully, COO of Anasazi Instruments. We have been serving the NMR community for 25 years. And over the last 10 years, I have helped over 4000 people like you choose an NMR spectrometer.
You may have seen benchtop and cryogen free NMR instruments from Bruker, Magritek, Nanalysis, Oxford, and Thermofisher.
Anasazi Instruments will soon add a benchtop to our line of NMR spectrometers.
So how do you choose the right benchtop NMR for your lab?
Here are 4 questions that you and your colleagues can ask yourself:
What benchtop NMR performance will I need for my application?
If you have a demanding application like analyzing unknowns, quantifying impurities, or looking at very dilute samples – then you will need higher performance. How do we measure the performance of an NMR system?
Here are three important performance metrics for benchtop NMR’s: resolution, lineshape and sensitivity.
Here’s how I like to think about it: Let’s take a look at a peak on an NMR spectrum. You want peaks that are sharp and narrow.
Or in other words, you want peaks with good resolution and lineshape.
The resolution of benchtop NMR’s range from 0.2Hz to over 1.5 Hz – and that is the width of the peak halfway to the top – we call that half height or half max. The lineshape for benchtop instruments ranges from 6 to 80 Hz. This is how wide the peak is near the baseline. Generally speaking, the narrower and sharper the peaks, the higher performing instrument you have.
Ok, so now let’s talk about sensitivity. This has to do with how tall the peak is in relation to how tall the baseline is. The height of the peak is our signal, and the height of the baseline is our noise. If you have a challenging application, then you will prefer an instrument that produces the tallest peak with the least amount of noise.
We report sensitivity with “signal to noise”. If you have an application that demands sensitivity the bigger the signal to noise ratio, the better.
Now here is the thing – Not all NMR companies use the same method or software to measure their sensitivity, so it’s sometimes difficult to directly compare sensitivity specs.
That’s why I would always recommend sending a sample to the benchtop NMR manufacturer. Get the real results and then you will know for sure if it will work for you or not. While that might not always be possible, I would recommend it.
One last comment on sensitivity: the signal to noise ratio varies by nucleus. So if you are studying nuclei other than protons, you will need to know the sensitivity for your specific nuclei. This is rarely reported so be careful and do your research.
How strong of a magnet do I need in a benchtop NMR?
Today’s range in benchtop NMR magnets is 1 to 2.35 Tesla or using frequency, as we more commonly do, 43MHz to 100 MHz.
How does magnetic field strength impact the results? Think of two peaks in a spectrum. You want those peaks to be separated, sharp, and have your results as fast as possible, right? – that is what magnetic field strength helps with.
Imagine – you have a NMR spectrum for a molecule and some of the peaks are very close to each other, maybe even overlapping. If you double the strength of the magnet you double the space in between the resonances.
So, increasing magnetic strength means you can analyze larger and larger molecules, more complex molecules with more and more peaks; obviously this is desirable. We just saw the installation of a 1.2 GHz or 25T magnet. Not a benchtop NMR – far from it! – benchtop NMRs have 1T to 2.3 T magnets. This is why the superconducting magnets used in NMR systems are called high field, whereas permanent magnet benchtops are considered low field NMR.
Generally speaking, a stronger magnet gives you the best chance to resolve all of those peaks. But, if you are comparing two benchtop NMRs with similar strength magnets, say 60 vs 80 MHz, you will only see a very modest improvement in peak separation.
Ok, now let’s go a little deeper on how magnetic field strength affects sensitivity. As the frequency of your magnet increases the sensitivity also increases. It increases substantially, and you get a lot of bang for your buck!
Let’s give an example: if all else is equal – same instrument design, same sample concentration, and you increase the magnet strength by 50%, then you will have an instrument that is twice as sensitive.
When you double the sensitivity you can get your results 4 times faster. This is particularly critical in carbon NMR. Let’s say that a carbon experiment takes 4 hours at 60MHz. The same experiment with the same sampe will take just 1 hour at 90MHz.
What if you don’t have the most powerful magnet? What can you do to compensate for the lower sensitivity? Well you could increase your run time, or increase the sample concentration. However, there’s still nothing you can do to compensate for peak resolution as modest as the improvements may be.
So to summarize, when you have a challenging application here’s what to look for in a benchtop NMR:
A combination of high sensitivity and resolution (including good lineshape), and a strong magnetic field.
What nuclei will I be studying?
Every benchtop NMR does proton NMR and they all do fluorine as well.
Of course you want to do proton NMR, but what if you also want to do carbon NMR spectroscopy? In this case you need a dual channel probe. All benchtop manufacturers except for ThermoFisher offer this capability.
Power users of benchtop NMR not only want proton, fluorine, & carbon NMR, but also other nuclei like phosphorus, lithium, boron, cobalt, and many more.
In this case you will need not just a dual channel probe, but a tunable dual channel probe. Only two manufactures offer this option – Oxford with their X-Pulse and Anasazi Instruments benchtop with our multinuclear option. For these two instruments, one channel handles proton and fluorine, the other is tunable to your nucleus of choice.
Now, if money is of no concern you could always buy multiple instruments: one dedicated to carbon, another dedicated to phosphorus, and a third dedicated to lithium for example.
Speaking of money, how much do you want to spend on a benchtop nuclear magnetic resonance spectrometer?
What is my budget?
Benchtop NMR prices range from about $20,000 to $120,000. The price depends on the magnet design, field strength, spectrometer performance, and probe capabilities.
Our Anasazi 60 MHz benchtop NMR will range from $40 to $55K.
Check out our article How Much Does an NMR Cost for more information on the current NMR market.
I would love to talk more about NMR with you.
Those are the four questions that I think you should ask yourself.
I hope this post helps you choose an NMR instrument that best meets your needs.
Nuclear magnetic resonance spectroscopy is an incredible technique that solves so many problems and has a wide range of applications. We want you to benefit from NMR and love it just as much as we do!
If you would like an even more in depth resource on Benchtop NMR performance, available experiments, software, magnet design, cost and other features please sign up for our “Comprehensive Benchtop NMR buying guide” using the form on this page.
I’ve talked with thousands of scientists, professors, and students about what they are looking for in an NMR, and I would love to hear from you too. Please reach out via our chat, email or call.
Chris Tully,
COO Anasazi Instruments
