Thermo Scientific picoSpin benchtop NMR spectrometers, like all modern-day benchtop NMR instruments, hold a steady field by heating a permanent magnet above ambient temperature and stabilizing it to a set point. Inside a picoSpin spectrometer this is consistent to one thousandth of a degree Celsius, i.e. 0.001°C. This precise temperature control is crucial for the instrument to function accurately and precisely, otherwise the Larmor frequency will drift around and acquisition of high-quality data becomes tricky. The temperature set point of a picoSpin spectrometer from the factory is ten or so degrees above an expected ambient temperature, but is user-configurable at installation. After switching on from cold it takes a little time to warm up and stabilize, even though a picoSpin spectrometer has considerably less mass of magnetic material to heat when compared to its counterparts at similar field strengths. Compare that also to a superconducting magnet, which takes a day or more to cool after adding cryogens and then the best part of another day to bring up to field. All analytical equipment is designed to work best in a regular laboratory environment, and the picoSpin spectrometer and other benchtop NMRs are no different. At a laboratory air temperature a few degrees below the set point and not in direct sunlight or in a draught, the picoSpin spectrometer will hum along contentedly for as long as the main electricity supply persists. If an uninterruptable power supply is in-line, either picoSpin model can easily be picked up and carried to a new location while at field, with only a brief shim at the destination before being ready to measure data again.
Recently I was working with my demo picoSpin 80 instrument in a lab and on the Temperature page in the interface, I noticed an interesting pattern of variation in the local temperature, as shown in Figure 1.
The instrument was set up in an air-conditioned lab with a relatively stable air temperature. That said, the picoSpin spectrometer clearly tracked the times when the air-con was on and when it was off (Ambient graph), and the picoSpin heater was inversely ramped up or down to compensate (Heater graph). It is worth noting that the ambient temperature shown is detected inside the instrument’s case – this is always a bit warmer than the external temperature. The top panel shows the magnet temperature with a variation of approximately 0.0005°C.
0.0005°C! There is a lot of clever engineering in these little machines.