Bruker Elesys E-540 System
Bridge
The microwave bridge of a spectrometer produces the microwave power and detects the EPR signal: its performance greatly determines the overall specifications of a spectrometer.The eleXsys series microwave bridges incorporate the latest state-of-the-art technology to provide the highest sensitivity measurements in different frequencies for eleXsys E 500/580 systems. It has two bands: the X-band, the most common microwave frequency because it combines high sensitivity with convenient sample sizes; and the L-band, for large biologicalor aqueous samples. (This instrument does not have in vivo imaging capabilities but it is suited to be upgraded by adding a few accessories). The L-band bridge can provide up to 400 mW microwave power for a variety of EPR studies. The frequency ranges from 1.05 to 1.15 GHz. When used with the large size L-band resonator, true in vivo EPR is possible. Other features: coarse frequency readout to 3 digits, or to a resolution of 1 kHz if the frequency counter feature (L to X band) is included, remote control of all bridges via the same control unit , protection against damage through user error, output power can be stepped in 1dB increments with an accuracy of typically +/- 0.2 dB from 0 dB to 60 dB, direct digital power readout in mW, W, or nW, high dynamic range AFC frequency locking, with frequency response and gain matched to the source oscillator characteristics, and finally, ultra low-noisemicrowave pre-amplifiers.
Resonators
The new Super High Sensitivity Resonator is the new standard resonator for the eleXsys line. It provides new levels of X-band CW flexibility. The quality factor (Q) of the resonator acts like an amplifier for both the incident power and the signal. Generally, a higher Q means higher sensitivity. However, also it needs to be considered the cavity's filling factor and the quality of the microwave source. The filling factor is the ratio of the integral of the microwave field over the sample volume relative to the integral of the total microwave field in the cavity. Classical high Q cavities such as the cylindrical TE0 have relatively poor filling factors, thus reducing the effect of their high Q. The new Bruker Super High Q (SHQ) cavity combines a super high Q (Qu >25000) with a large filling factor and large modulation coils. Combined with a specially tuned low noise Gunn source bridge, and the SignalMaster, the SHQ provides the ultimate in sensitivity. The cavity provides outstanding performance with powder, single crystal and even aqueous samples. Its auto tune capabilities make it as easy to use as a standard cavity.
Magnet
The (10” pole cap diameter) precision magnet is water-cooled, with the water flow in series with the power supply. Thermal and current control interlocks are provided, and overload warning LED's indicate phase failure, current overload, cooling water failure and temperature variations. The larger magnet yokes are made from one solid piece of soft iron to provide the mechanical stability required for long-term stability and homogeneity under varying conditions.
Temperature Controller for Liquid Nitrogen
The Digital Temperature Control System, ER 4131VT, makes use of liquid or gaseous nitrogen as coolant. The accessible temperature range is 100 K to 500 K. The base system consists of the following parts:
- Quartz Dewar
- ER 169DIS Dewar Insert Holder
- Digital Temperature and Gas Flow Control Unit
- Thermocouple
- Transfer Dewar
- 10 L storage dewar
- Nitrogen Evaporator Heater Assembly
With the dewar insert holder, the dewar is mounted to an X-Band waveguide-type cavity. The sample is inserted into the quartz dewar. Sample exchange at any temperature is a standard feature of this system. The digital control unit monitors and controls the temperature measured with the thermocouple close to sample's position. The target temperature is reached and stabilized via PID temperature control (proportional, integral and derivative). The control unit is fully remote controlable via the acquisition software Xepr or WinEPR Acquisition of the ELEXSYS and EMX spectrometer series. A Manual Control Unit (ER 4131-1030) is available for manual control of the heater and the gas flow.
ER4141VT-M Metal-Transferline Option: To further enhance the hold time and ease of operation, the ER4141VT-M is offered. This temperature system includes a large 25 L storage dewar and a metal transfer line.
Cells
Flat cell: If the EPR samples contain water, problems will arise with coupling the sample in a cylindrical EPR sample tube. Because of its large dielectric constant, water is highly ‘lossy.’ A large amount of microwave energy is absorbed by water-containing samples, reducing resonator Q and observed resonator performance. Lossiness is due to the strong interaction of the electric component of the microwave field with the strong dipole of the water molecule. If the sample is small, we will use capillary tubes to reduce the exposure of the sample to the electric field. For samples between 100 and 300μl, the solution is to turn to a ‘Flat’ sample geometry. Aqueous (Flat) and Tissue Cells reduce lossiness by confining a water-containing sample to the magnetic field. The electric field sees only a very thin sample (usually 0.3mm).
Tissue cell: Aqueous Sample Cells can only be used when your liquid sample can be pulled into the cell using vacuum or the viscosity is low, using gravity. However, if the sample is viscous or tissue slices need to be studied, then Tissue Sample Cells are ideal for studying wet tissues and polymers, e.g. epithelial slices, using EPR. The EPR Tissue Cells are prepared from high quality Clear Fused Quartz or Synthetic Suprasil plates. All cells include a 0.5mm deep well for thick samples. The sample goes between the plates, like a microscope slide. It comes with two support rods. The top rod has flats cut into the end to help you align the cells inside your resonator. Each cell includes two cover slides and two ‘Bronzite’ clips.
AquaX cell: AquaX is a new Bruker product specifically designed for aqueous solutions and other lossy liquid samples. An innovative multibore design provides maximum sensitivity, while minimizing sample volume. The cylindrical design of AquaX makes tuning much easier than with the traditional flat cell and also improves sample-to-sample consistency. It is made of chemically resistant materials and is available in two versions for X-band, one with a 30 ml/cm volume and one with an 18 ml/cm volume. Two sizes of Teflon transfer tubing are also available (0.03”I.D., 4.56ml/cm and 0.02” I.D., 2.03 ml/cm). The user can vary the sample volume used in the experiments by simply cutting the transfer tubing to the appropriate length.
Computer/Software
The EPR equipment uses a pentium-based PC with a Linux operating system. Xepr is a complete data acquisition and processing package for all eleXsys system consoles.
It provides a user-friendly, flexible and complete control over all hardware functions, and offers a comprehensive assortment of tuning and calibration routines. An extensive assortment of display tools and processing elements allow you to fully realize the potential of Xepr's data acquisition. Xepr allows the creation of macros and automation routines, making it entirely customizable. A comprehensive help facility allows performing keyword searches in the help dialog box or consulting the on-line Xepr manual written in Adobe Acrobat. It is possible to write help segments for our own macros and ProDeL programs and implementthem into the help facility. It has a versatile data acquisition that allows to do the following tasks: Tune and calibrate with ease, adjust parameters interactively, create unique 2D experiments, automate acquisitions, use multiple viewports to control different experiments, link different experiments for interactive control. It has a flexible data processing that allows to manipulate spectra using interactive tools, easy access to a variety of fitting and processing functions using the task bar, create custom macros and custom tools, use ProDeL to make unique automated processing and acquisition routines, link acquisition and processing in one seamless routine.