4. NMR system overview

Each spectrometer consists of three main components:

Figure 4.1: The main components of an NMR spectrometer

The entire system is controlled nearly 100% from the host computer. The only exceptions are: inserting/removing the sample, tuning the probe (if necessary) depending on the sample (solvent, concentration, salt content etc.).

Input into and control of the system is via keyboard or a three-button mouse:

Figure 4.2: Three-button mouse

4.1 Probes and other hardware

The 300 and 600 MHz systems are designated as proton NMR systems with indirect detection of heteronuclei. All others can observe heteronuclei directly. A comparison of available probes and feasible experiments is given in the Table below:

* spectrometer and probe dependent

4.2 Sensitivity and spectral dispersion

Spectral dispersion is proportional to the field strength hence a 500 is 66% better than a 300 while a 600 is twice as good as a 300. The probability for spectral overlap in a two-dimensional experiment decreases significantly with increasing field strength:

300: 1.0         400: 0.56        500: 0.36        600: 0.25

The sensitivity for protons and resulting experimental times or sample concentration, respectively, to reach the same signal-to-noise ratio is compared below:

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