Parameters
or
You Might Need This For Your Thesis Defence (hint, hint)

The Bruker software, Xwin-nmr, is extremely configurable with many hundreds of parameters that affect the way data is acquired, processed and plotted. You cannot effectively operate one of these machines manually without a basic knowledge of the main parameters. You should at least know what the parameters that are printed with the spectrum mean. You never know ... someone on your thesis defence committee might decide to ask you what 'AQ' means. How would you answer. What happens to 'AQ' if 'SW' is decreased? What is the effect on a 13C spectrum if 'D1' is decreased? Consider yourself warned.

Xwin-nmr has several parameter editors:

  • eda - acquisition parameter editor
  • edp - processing parameter editor
  • edg - plot parameter editor
  • edc - data set editor
  • edpul - pulse program editor
  • edasp - nucleii/channel routing editor
  • edcpul - current pulse program editor
  • edlist - list editor
  • ased - automation setup editor

In order to effectively use the machine you need to know how to use these editors. The best way is to 'play' with them and see what happens to the spectrum. One warning, however ... don't change any power levels unless you really know what you're doing, especially for homodecoupling and NOE experiments. You can damage the equipment by using pulse power levels that are too high.

Now, let's look at the common parameters that are printed with your spectrum. I should say that this is just a very small subset of the parameters available to you withing the program. Starting at the top of the list:

  • Name - the name of the folder in which your data will be stored. This folder will contain several sub-folders .. below 'Name' is 'nmr' and below 'nmr' is 'expno', the experiment number. You would use different experiment numbers for different experiments on one sample. For example, you might want to do a 1H, a 13C, an HMQC and a HMBC experiment on your sample. the 1H could be experiment number 1, the 13C experiment number 2 etc. Your data are then organised hierarchically under 'nmr'.
  • Expno - experiment number (see above)
  • Procno - processed data set number. You can process one data set in more than one way and store the results in separate numbered folders. Most people would not have occasion to do this but it is possible.
  • Date - the date (duh!)
  • Time - the time
  • Instrum - the instrument that the spectrum was done on. The Bruker default is 'spect' which is what each of our machines is set to. We could change this on our machines to relect the identity of each of them but this is a rather tricky thing to do.
  • Probhd - the probe that was used for the experiment.
  • Pulprog - the pulse program that was used to acquire the data.
  • TD - the time domain. This is the number of data points that were digitised. Thus, a value of say, 16384 would mean that this many data points were used to digitise the spectrum.
  • Solvent - the solvent that the sample was locked with
  • NS - the number of scans
  • DS - the number dummy scans. These are used to get the spin system into a 'steady state' before acquisition begins.
  • SWH - the 'sweep width' in hertz
  • FIDRES - the fid (Free Iduction Decay) resolution in hertz per point. This is calculated by dividing SWH by TD.
  • AQ - the acquisition time. This is the length of time that the digitiser is on, acquiring data.
  • RG - the receiver gain. This parameter is usually set automatically when the 'rga' (receiver gain automatic) is issued.
  • DW - dwell time. The is the time interval between data samples taken from the analog signal by the digitiser.
  • TE - the temperature that the spectrum was acquired at.
  • D1 - the interpulse delay time.
  • NUC1 - the F1 channel (the acquisition channel) nucleus. This is the nucleus that the observed signal is received from. F1 is always the acquistion channel ... F2, F3 etc are decoupler channels.
  • P1 - the pulse 'width' used for pulses on the F1 channel ... it is actually the time during which the transmitter is on, irradiating the sample with rf energy.
  • PL1 - the attenuation setting for the power amplifier. This is a number which sets the power of the signal irradiating the sample in dB. It can be somewhat confusing until you get used to it. The larger the number the higher the attenuation and the lower the power is.
  • SFO1 - the transmitter frequency in megahertz. This the sum of BF, the basic frequency of the spectrometer plus O1 the offset frequency.
  • ND0 - number of D0 delays. This is used only in 2 dimensional experiments and indicates the number variable D0 delays there are in the pulse sequence.
  • SI -