All benchtop manufacturers except for ThermoFisher offer this capability. 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. So to summarize, when you have a challenging application here’s what to look for in a benchtop NMR:Ī combination of high sensitivity and resolution (including good lineshape), and a strong magnetic field.Įvery benchtop NMR does proton NMR and they all do fluorine as well. However, there’s still nothing you can do to compensate for peak resolution as modest as the improvements may be. 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. The same experiment with the same sampe will take just 1 hour at 90MHz.
Let’s say that a carbon experiment takes 4 hours at 60MHz. This is particularly critical in carbon NMR. When you double the sensitivity you can get your results 4 times faster. 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. It increases substantially, and you get a lot of bang for your buck! As the frequency of your magnet increases the sensitivity also increases. Ok, now let’s go a little deeper on how magnetic field strength affects sensitivity. 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. Generally speaking, a stronger magnet gives you the best chance to resolve all of those peaks. This is why the superconducting magnets used in NMR systems are called high field, whereas permanent magnet benchtops are considered low field NMR. Not a benchtop NMR – far from it! – benchtop NMRs have 1T to 2.3 T magnets. We just saw the installation of a 1.2 GHz or 25T magnet. So, increasing magnetic strength means you can analyze larger and larger molecules, more complex molecules with more and more peaks obviously this is desirable. If you double the strength of the magnet you double the space in between the resonances. Imagine – you have a NMR spectrum for a molecule and some of the peaks are very close to each other, maybe even overlapping. 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. How does magnetic field strength impact the results? Think of two peaks in a spectrum. 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 strong of a magnet do I need in a benchtop NMR? This is rarely reported so be careful and do your research.
So if you are studying nuclei other than protons, you will need to know the sensitivity for your specific nuclei. One last comment on sensitivity: the signal to noise ratio varies by nucleus. While that might not always be possible, I would recommend it. Get the real results and then you will know for sure if it will work for you or not. That’s why I would always recommend sending a sample to the benchtop NMR manufacturer.
#Inmr add structure to nmr software#
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. If you have an application that demands sensitivity the bigger the signal to noise ratio, the better. We report sensitivity with “signal to noise”. If you have a challenging application, then you will prefer an instrument that produces the tallest peak with the least amount of noise. The height of the peak is our signal, and the height of the baseline is our noise. This has to do with how tall the peak is in relation to how tall the baseline is. Generally speaking, the narrower and sharper the peaks, the higher performing instrument you have. This is how wide the peak is near the baseline. The lineshape for benchtop instruments ranges from 6 to 80 Hz.
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. Or in other words, you want peaks with good resolution and lineshape. You want peaks that are sharp and narrow. Here’s how I like to think about it: Let’s take a look at a peak on an NMR spectrum. Here are three important performance metrics for benchtop NMR’s: resolution, lineshape and sensitivity. How do we measure the performance of an NMR system? If you have a demanding application like analyzing unknowns, quantifying impurities, or looking at very dilute samples – then you will need higher performance.
What benchtop NMR performance will I need for my application?
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