NMR Processing: Add a Series of FIDs

For long-term measurements, I usually recommend to split up the measurement into shorter pieces. Possible advantages:

• in case of electrical power or hardware failures, chances are that there are still some FIDs available;
• if the sample reacts or decomposes, the series of spectra will give a clue.

The TopSpin automation program multizg facilitates the acquisition of such sequential experiments. Another automation program makes it easy to add together the resulting individual FIDs. The following section describes the procedure.

1. FIDs to be added should have been acquired under identical conditions (i.e. spectral width, transmitter frequency), the number of scans does not matter
2. the data sets must have sequential experiment numbers
3. there can be data sets afterwards with sequential experiment numbers that should not be added; fidadd will use the next free slot
4. read the first FID of the series (not necessary, but simplifies the procedure)
5. issue the command fidadd (on first use, TopSpin will need to compile the script)
6. answer the on-screen questions or accept the defaults (data set name. paths etc. should be correct), but pay attention to the number of experiments if there are dataset following that should not be added
7. usually, TopSpin will switch to the new data set that contains the sum of all FIDs
8. TopSpin will adjust the number of scans. N.B. the number of scans shown as NS under AcquPars or reported for the command ns are foreground parameters; if we issue the command go, TopSpin will acquire and add to the existing FID the corresponding number of additional scans. The actual number of scans co-added into the current FID is a status parameter, you have access to that number if you hit the button "S" under the AcquPars register.
    
    
   In this example, seven experiments with 1600 scans each and one with 312 scans have been coadded, resulting in a total of 11512 scans.