SETTING UP YOUR EXPERIMENT
   
Designing an NMR experiment:
Number of data points.
  NMR signals are recorded digitally, i.e., as a series of discrete, evenly spaced data points, rather than as a continuous stream of information. It is critical to collect sufficient data points so that the signal can be accurately represented. The example below shows a curve that is well-defined, in spite of the fact that there are relatively few points (an actual NMR experiment would use many, many more); all of the maxima and minima are included, and subtle, small oscillations are also captured. Position your mouse over the image to view a data described by too few points; it would be impossible to accurately reconstruct the original signal from this information.
 
 

The digital resolution is given in Hz/point, and is equal to the sweep width divided by the number of data points. Thus, if a 2400 Hz width is described by 16384 points, each point represents 0.146 Hz (2400 Hz/16384). The acquisition time (the period over which data is recorded) is the reciprocal of the digital resolution; for the case discussed above, this is 6.85 seconds (1/0.15 Hz = 1/0.15 s-1)
   
  If the acquisition time is too short, the NMR signal will be truncated (cut off) in the time dimension, leading to baseline artifacts, such as those shown below (position your mouse over the image to view examples of these distortions).
 
  Since modern NMR instruments are not memory-limited, truncation errors are now rarely a concern in simple experiments. If they are an issue for a particular sample, the solution is to simply increase the number of data points, thus extending the acquisition time (and, as an added bonus, enhancing the data density). Note that data points are usually chosen as powers of two, rather than multiples of ten, so that, on the first attempt, the number of points would be doubled. The other option, that of increasing the sweep width, takes in a wider frequency range which probably contains no resonances; this action contributes nothing to the quality of the final spectrum.
 

 
  NOTE: The powers of two typically used to set the data points in NMR experiments are: 128, 256, 512, 1024 (1k), 2048 (2k), 4096 (4k), 8192 (8k), 16384 (16k), 32768 (32k), 65336 (64k), and 131072 (128k). For simple experiments, the number of data points is usually between 4k and 64k.