UW CHEMISTRY NMR

I am motivated to post this in the wake of ATMA problem with the AV301 probe but, this is generally applicable to both the 300 MHz systems and the new probes with ATMA capability we will get in the near future.

Message :  Always LOCK first on your solvent BEFORE you attempt ATMA. 

ATMA program maintains a table where it stores the positions of the motor elements that are used to crank the Tuning and Matching capacitors in the probe electronics.  These positions are stored for each and every Lock solvent that is used.

The Capacitor values that give correct resonance condition are highly dependent on the Lock Solvents. 

If you do not lock on your correct solvent first, then the software uses the stored parameter for the last lock solvent and refers to the corresponding value from the table. There are at least two problems, with this :

• There is no guarantee that the last solvent used by a different user was the same as your sample’s solvent.
• ATMA software starts with the wrong beginning values for your sample tube.  The optimization algorithm, as a result, can diverge and leave the capacitors at their mechanical extreme and fail.

Even if the optimization converges, the software will now store the wrong motor element positions for the wrong solvent it assumed ! – a double whammy of sorts !

ALWAYS, lock on your correct solvent FIRST thing before you run ATMA.

Thank you for your cooperation and attention.

NMR Facility Manager

9.19.2022