#Product Trends
Benchtop Solutions Broaden NMR Use
Smaller, more technologically advanced NMR systems have helped broaden the use of the measurement solution.
The latest analytical technology to move to the benchtop is nuclear magnetic resonance (NMR). High-end, high-cost instrumentation has dominated the NMR sector for many years with the costs of both instrument purchase and annual running putting it way out of reach from the basic laboratory budget. Specialist is the word that would come to mind. A special room with special supplies and, not least, a specialist to run and interpret the data produced.
This could be compared to where mass spectrometry was 20 years ago, but look where it is today—buyers now have the option of multiple suppliers to choose a system with a benchtop footprint. The last 12 months has seen the world of NMR make similar strides with the arrival of several new models and suppliers. Some questions about the present and current state of NMR include: what technology changes have made benchtop NMR a feasible system?; how will the new systems impact purchase and running costs?; and which groups of users are likely to benefit the most?
Technology breakthroughs
The biggest breakthrough in technology has been the advent of new magnetic materials to produce “Halbach” magnets. These do away with the superconducting magnets of the high-frequency top-end NMR spectrometers. Much smaller permanent magnet technology using rare earth minerals have removed many of the barriers associated with older high-technology superconducting magnet systems. These offer great stability and uniformity of field to enable the use of standard NMR sampling tubes, the same as used in the older systems.
These new benchtop systems can also operate at much lower frequencies, e.g. 42 MHz, compared to the high-field systems that operate at frequencies as high as 900 MHz. At first glance, it would seem unlikely that a meaningful result could be obtained with a measurement made at such a low frequency. However, the performance of these permanent magnets is such that the resolution differences and system sensitivity are more than adequate for the majority of analytical tasks. This in itself is a huge benefit. It is a great breakthrough to be able to produce a smaller instrument without the need for the safety precautions required for high-field units, yet achieve performance to meet the regular analysis needs of chemists who have no time to send samples out for measurement.
Cost
Price is commonly a driver in the purchase process of a new or even replacement instrument. With prices dropping by an order of magnitude to less than $100,000, this is opening up demand from industry and smaller colleges with limited research capabilities, together with undergraduate courses looking for teaching instruments that deliver a system that is easy for students to use quickly.
Not needing a specially constructed room with shielding is a huge bonus. The ideal requirement for the benchtop system is to be able to place it on the appropriate lab bench; just plug it into a single power socket and start taking measurements. This is now feasible.
The same goes for consumables. High-specification NMR systems operate with cryogens, such as liquid helium. Not only is liquid helium very expensive, but there is a supply shortage and a risk on its long-term availability at a reasonable price. No cryogens are needed for the new generation of benchtop systems.
Beneficiaries
The world of organic chemistry is the principle benefactor for the advent of benchtop NMR spectrometers. Whether the user is in academia, research, chemical or pharmaceutical industry, the key goal of any analyst synthesising products is to be able to quickly and reliably identify the end product. NMR is the ultimate technique for this. While mass spectrometry, IR and UV spectroscopies are widely used, it is only NMR that can provide a definitive analytical answer independent of molecular weight.
While an NMR system offering a basic single proton (1H) analysis is useful as a simple teaching tool, it has always been the goal of instrument designers to offer a more capable system. The Spinsolve Carbon spectrometer from Magritek, New Zealand, is a step in that direction.
For organic chemists, carbon-13 (13C) NMR forms the backbone of routine molecular analysis. Users have the power of a 1-D and 2-D proton-carbon NMR in a benchtop instrument that can be safely used in the laboratory. Typically, users are split into a few categories: pharmaceutical and medicinal chemists, synthetic chemists, academics focused on organic chemistry education and researchers working on the structure elucidation of organic molecules.
Spinsolve Carbon offers users 1-D 1H, 19F and 13C experiments that use standard 5-mm NMR tubes. 13C experiments include spectral editing with DEPT, 2-D direct HETCOR experiments and 2-D indirect experiments, such as HSQC, HMQC and HMBC. For proton 2-D, COSY and homonuclear j-resolved spectroscopy are offered along with T1 and T2 relaxation experiments.
Carbon-13 NMR spectroscopy delivers more detail in its spectra than use of the more basic 1H nucleus alone. Carbon-13 has a large chemical shift range of approximately 250 ppm, and with composite pulse decoupling there is usually a single peak per carbon atom in the molecule, making carbon spectra more informative than proton spectra. Furthermore, multi-nuclear and multi-dimensional experiments reveal additional structural information, such as how carbon and proton atoms in the molecule are connected. This enables NMR to easily resolve isomers that are often confused with other analytical methods.
Applications
One application of benchtop NMR enables synthetic chemists to monitor chemical reactions in real-time to check reactants, follow the reaction and determine its endpoint. This is illustrated with a simple acetalization reaction with the Spinsolve system by using a flow tube passing through the spectrometer, as shown on the previous page.
The software collects a 1-D proton NMR spectrum every 30 seconds and the reaction is followed for just over 1 hour. This application clearly shows the quantitative nature of NMR, enabling chemists to follow the reaction as it is occurring without the need for chemometrics and other advanced analysis methods that are necessary for monitoring reactions with infrared spectroscopy.
Benchtop NMR spectrometers are playing a significant role in making NMR available to a much wider audience than in the past. Just as with high-field NMR where advanced multi-dimensional and multi-nuclear methods enabled NMR to tackle larger molecules with overlapping 1-D spectra such as proteins, the same techniques can be used with lower field benchtop NMR spectrometers to widen the range of molecules that can be successfully measured.
Benchtop NMR enables the spectrometer to be taken to the sample, and opens the door for NMR to be used in the chemistry lab, industry lab or even factory floor, where it was previously impossible to consider such a measurement solution.
