Problem: An NMR tube is a thin glass walled, closed bottomed tube used to contain NMR solution samples. Its purpose is to confine a liquid sample in a perfectly cylindrical volume in a magnetic field. There are a variety of NMR tubes available on the market from a number of different manufacturers, however, it cannot be overlooked how important correct tube selection is for ensuring quality and reliability of your experimental results. It is possible to select NMR tubes from a huge variety of qualities, with an equally significant difference in price between the cheapest and the most expensive. They are rated according to many parameters and not in a conventional way—but what is the difference between these different NMR tubes? How varied is the effect on the quality of the spectra and how do you know the right tube to pick for your experimental requirements?
Solution: Historically, it had been the norm to pick tubes based on factors such as thickness, concentricity, and camber. However, the key to purchasing the right NMR tube for your needs is to keep focused on the application being carried out and pick the most suitable tube for your application. A shift in thinking is needed to start with the application and system configuration rather than with the tube properties. The industry is supporting this focus on application and experimental need by offering a service to scientists that helps them to determine the most appropriate tubes rather than simply offering the tubes by properties alone.
NMR tubes can be split into three different application approaches:
- For day-to-day use in an environment of low to medium throughput, providing the best balance between quality and price
- For medium to high throughput with use of a sample loader, these tubes are designed to support the user in achieving reliable, repeatable results
- For high quality and high precision work, best for achieving repeatable, reliable results with very limited impact of background noise
Once the user has established their application into one of the above three categories they can move forward to the right standard tube for their requirements. Therefore, they need to keep in mind the application, sample requirements, and hardware. Once this is completed, the specific structural properties of the tubes can be evaluated in how they impact experiments. The table below provides an initial guide:
|NMR instrument performance/application||Structural Specs|
|Experimental Temperature||Glass Type|
In addition to standard NMR tubes, specific sample/ applications require specialized tubes. One example is Microscale NMR tubes for specialized NMR experiments. These are most appropriate where only a small sample is available; for example, for protein experiments on high field NMR spectrometers. Microscale NMR tubes are available with their construction optimized for various solvents including D20, CDCI3, DMSO-d6, and CD3OD and for probe type, RT probes or Cryoprobe™. These tubes allow for the restriction of the active volume and hence reduce the amount of solvent used without causing line shape problems. Another example is NMR microscopy tubes. Here, samples are not solution, but objects, typically live objects such as animals and plants and inanimate material samples for application in many different fields of research. These can include physics, chemistry, biochemistry, biology, medicine, food technology, materials science, chemical engineering, among others.
All scientists are seeking accurate, reproducible results and the effect of choosing the correct NMR tube cannot be overstated.
For more information, please visit: https://www.bruker.com/service/service-units/labscape-service-and-life-cycle-support/consumables.html
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