Modern NMR spectrometers host a myriad of improvements over the Varian A-60, allowing modern instruments to solve problems that spectroscopists in the 1960s could not have dreamed. Modern NMR techniques are capable of investigating chirality, protein structures, even kinetics in some cases. NMR is quickly becoming the tool of choice for many biological applications, particularly those in fluid environments.

Almost all NMR spectrometers today use a technique introduced in the 1970s called pulsed field Fourier transform NMR spectroscopy, or FT-NMR. Though the title is complicated, the idea behind this technique is not as difficult as it sounds.

The A-60 and other older NMR spectrometers are now called continuous wave (CW) NMR spectrometers because the magnetic field of these instruments did not change over time. In fact, any variations in the magnetic field were carefully eliminated to avoid inconsistent baselines and other errors. These early NMR instruments induced a magnetic field around the sample to align the nuclei, then induced a second magnetic field perpendicular to the first. The second field, if the frequency was just right, resonated with certain nuclei and knocked them over, producing an NMR spectrum by recording the frequencies at which energy was absorbed. Therefore, the information we want is the frequency at which each nucleus is precessing in the original magnetic field.

A pulsed field NMR spectrometer still uses a first magnetic field to align the nuclei, but the second magnetic field is applied very differently. Instead of applying the field and scanning through the frequencies, all the frequencies of the perpendicular magnetic field are applied together, knocking over all the resonant nuclei in the sample at once. As the spinning nuclei realign themselves to the original magnetic field, they are constantly spinning. These spinning electric charges induce an oscillating current in a receiver as they reorient themselves to the original field.

The NMR spectrometer collects this data, which, as you might expect, is very complicated because all the resonant nuclei precess and decay at different rates depending on their local electronic environments. If one were to look at this data, it would look much like an interferogram, the same kind of data generated by a modern infrared instrument. A computer takes this interferogram, and by Fourier transforming the interferogram, generates a standard NMR spectrum. A Fourier transform is just a mathematical operation by which a complex curve, in this case an interferogram, is translated into many simple curves. In other words, the Fourier transform is able to look at a complex set of data from all the spinning nuclei and separate it into data on each individual spinning nucleus. This data is then plotted to make a familiar NMR spectrum.

The advantages of FT-NMR spectroscopy are increased resolution and sensitivity, which are major advantages in any analytical technique. The use of FT-NMR has allowed scientists to do correlational 2-D NMR studies and many other experiments, even to the point of determining the fluid structure of entire proteins. The increased sensitivity of FT-NMR is one of the main reasons why heteronuclear NMR spectroscopy has become more prevalent.