Spectrometer magnetic-field meter

Ultraviolet and visible spectra were recorded with a Beckman DK-2 or Cary 14 spectrophotometer. ESR spectra were measured with a Varian model 4500 ESR spectrometer with 100-kHz field-modulation and detection. The klystron frequency was measured with a transfer oscillator and a frequency counter. The magnetic field was measured by a proton gauss meter monitored by the same frequency counter. 

On the other hand, the development of compact mass analyzers, which are easy to use and fully controlled by data systems, led to mass spectrometers no longer covering an area of some square meters (as the early magnetic sector-based ones), but bench top machines, whose dimensions are sometimes smaller than those of the chromatographic devices with which they are coupled. Most of these instruments are based on the interaction of ions with quadrupolar electrical fields and were developed by the W. Paul (Nobel Prize for Physics, 1989) group at Bonn University. 

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