Flexible EPR Spectrometer Designed for Research: ELEXSYS-II

The ELEXSYS-II EPR spectrometer range from Bruker BioSpin is a research platform that offers excellent flexibility and performance. The ELEXSYS-II EPR system, which is a comprehensive range of EPR solutions and spectrometer versions, represents an essentially new technique for EPR instrumentation.

The ELEXSYS-II range offers solution-oriented spectroscopy, necessitating the most advanced hardware and an excellent EPR software approach.

ELEXSYS-II Upgrade Pathways and Multifrequency

Using the imaging accessory, the DICE-II ENDOR equipment, microwave bridges, and the FT system, it is possible to expand the ELEXSYS-II spectrometers from 1 to 263 GHz for FT and/or CW operation. This facilitates real multi-resonance and multi-frequency EPR.


ELEXSYS-II has complete network capabilities and has been designed for open-ended expandability. The system can be operated by a single user or an entire group, where the group members may be at different places.

The Client/Server architecture resolves the conflict between not only multi-tasking/multi-user but also real-time functions.

The ELEXSYS-II range has been equipped with the following comprehensive software packages:

  • FDepr for controlling the DeviceNet, the high-speed communication between the Functional Devices of the spectrometer and the server
  • Xepr for data display and processing
  • Aepr handles for 1D/2D data acquisition

Disentangle Magnetic Field Dependent from Independent Terms

Multi-frequency EPR is the mechanism for disentangling magnetic field dependent from independent terms. The EPR product range from Bruker BioSpin now includes two orders of magnitude in microwave frequencies:

  • L- and S-Band—1 and 3.5 GHz
  • X-Band—most common frequency at ca. 9.8 GHz
  • K- and Q-Band—24 and 34 GHz
  • W-Band—94 GHz
  • Millimeter-wave—263 GHz

Image Credit: Bruker BioSpin

Although high-frequency EPR offers evident benefits, the ideal choice for large samples and specifically for in-vivo studies (ELEXSYS E540) is the low-frequency EPR.

Multi-frequency EPR spectra make simulation (for example, with Bruker Biospin’s XSophe) considerably more effective. Moreover, it would be possible to study motion effects over a broad temporal range.

Multi-Frequency CW-EPR

Most of the CW-EPR systems work at X-Band. Therefore, the primary step into multi-frequency CW-EPR is to use another operation frequency. When it comes to standard CW-EPR spectroscopy, Q-Band at 34 GHz would be the ideal choice. This is because:

  • It offers three times greater Zeeman energy
  • It probes using an optional window, or makes ENDOR capabilities available
  • Sample size is still relatively large with 3 mm o.d.

Image Credit: Bruker BioSpin

The table below offers a list of the most common EPR frequencies, including their frequency range and g = 2 field value for radical species, respectively. All these frequencies are generally available in Bruker Biospin’s choice of magnet systems.

Microwave frequency bands and magnetic fields. Source: Bruker Biospin.

  L S X K Q W
v (GHz) 0.8-1.2 3.4-3.8 9-10 24 34 94
g = 2 (kG) 0.35 1.3 3.4 8.5 12.2 33.5


Multi-Frequency FT-EPR, ENDOR, and ELDOR

Bruker BioSpin’s multi-frequency EPR is not restricted to just CW-EPR. The EPR product range from Bruker BioSpin enables real multi-resonance and multi-frequency EPR, ENDOR, and ELDOR both in Pulsed and CW mode. With the help of the Intermediate Frequency (IF) concept, it is possible, for instance, to readily upgrade an X-Band E580 system to Q-Band (SuperQ-FT).