Varian Mercury versus Bruker Av3

Our laboratory has instruments from two Manufacturers: Varian and Bruker.

Our Varian instruments are both a early-mid  1990 vintage. Our Bruker spectrometers are of the AV3 and AV3-HD generation, which were produced from the ~2010 until ~2016. The company Varian was one of the pioneers in commercial NMR spectrometers. Unfortunately it sold off its NMR division to Agilent in 2010, which then decided to exit the NMR business in 2014.  Regrettably this ended a healthy competition with Bruker, a competition, which lead to important innovations in the field of NMR. However, in my opinion my opinion depsite the loss of a real competitor Bruker has continued the development of NMR technology. 

So what is the advantage of a modern Bruker 400 MHz NMR spectrometer over a Varian spectrometer, which is older than almost all of our graduate students? 

  • The probe and electronics is more sensitive.  This will become relevant for nuclei other than 1H.   However, the difference is really not that relevant when it comes to the “quick 1H spectrum”. 16 or 32 scans measures a decent 1H spectrum on both platforms provided that the sample is well prepared.
  • The modern instrument comes with a great variety of experiments. Bruker instruments come with an extensive library of pulse sequences and associated parameter sets.  Out of those not all will run on a basic 400 MHz instrument.  But there is a whole set of 2D experiments, which run well on the Bruker experiment; for the Varian instrument it is not even worth trying to get these experiments to run.
  •  The Bruker instrument (at least in our  AV3 version) can run nuclei other than 1H and 13C. In fact, we routinely run 19F and 31P experiments on our Bruker spectrometer. We have conducted NMR experiments of many other nuclei (29Si, 27Al, 11B, 109Ag to name just a few).
  •  The Bruker instrument has a gradient probe. In addition to sending and receiving radio-frequency pulses the probe has also the option of sending pulsed magnetic field gradients. I.e. the usually very homogeneous magnetic field can be made inhomogeneous in a controlled manner. This opens the door for many new experiments such as the DOSY experiment, which correlates the diffusion coefficient for Brownian motion with the chemical shift of molecules. Gradients also help to eliminate the need for complex phase cycles, i.e. they remove unwanted magnetization components which are generated during 2D experiments, therefore leading to cleaner spectra, which can be recorded in a shorter acquisition time.
  • The operation of the Bruker instrument is more automated. The command “atma” automatically tunes the probe, i.e. stepper motors automatically adjust the resonating circuit in the probe to be on-resonance with the desired measuring frequency. Then the command “topshim” starts an automated sequence leading to an automatic adjustment of the shim coils to achieve a homogenous magnetic field.  The automation of adjustments procedures facilitates the operation of the instrument; more important it makes the recording of spectra more reproducible and independent of the operator. The Varian Mercury spectrometer has a pre-tuned probe, where tuning of routine samples is not required. Shimming must be done manually, by adjusting shim currents and watching the intensity of the 2H signal (lock) on a clock-like display.

Does the Varian instrument have one advantage over the Bruker instrument?  Yes it does. A skilled operator can easily achieve a good shim in a shorter amount of time than Bruker’s Topshim software. So the simple 1H spectrum can be recorded quicker on the good old Varian instrument than on a modern Bruker instrument. And sometimes it is just cool to go vintage!  

Leave a Reply

Your email address will not be published. Required fields are marked *