Department of Chemistry, Tufts University

Bruker EMX EPR Spectrometer –Basic Operation

This brief guide covers only the most basic information for EPR operation. Please refer to the Manual, “EMX EPR Spectrometer” especially Chap 3,4 for further information.

Turn On Sequence

1. Sign the log book.

2. Turn on cooling water. Valve handle parallel to pipes is ON.

3. Turn on Heat Exchanger. Switch is on front, upper right.

4. Turn on Electronics cabinet. Switch is on back, lower left.

5. Turn on computer. Start EPR Acquisition program

6. Turn on Magnet Power supply.

Automatic Tuning

1. Insert sample, using appropriate collet. Bottom of tube should be about 100mm from top of collet. If the VT unit is installed there is no mechanical stop.

2. Select Parameter/Bridge Control from the menu or icon from Toolbar

3. Select Tune, then select one of the Autotune arrow buttons.

4. When the rough Autotune completes, select the Fine Tune button

5. If the Autotune is successful, The OPERATE, LEVELED, and CALIBRATE indicators on the upper left will be green, and the AFC, Diode, and Receiver Level meters will be approximately centered (in green zone).

Manual Tuning

1. If the Autotune is unsuccessful, the spectrometer must be tuned manually.

2. In the Bridge control window, select Tune, Set attenuation to 25.

3. Adjust Frequency to center the dip on the display. Adjust Phase for a symmetric dip.

4. Select Operate. Adjust Frequency to center AFC meter.

5. Set attenuation to 50. Adjust Bias to center diode meter. Decrease attenuation by 10db. Use the Iris ­¯ buttons to keep the Diode meter centered. Readjust Frequency to center AFC meter if necessary. Continue decreasing attenuation until attenuation is 10, readjusting Iris as needed.

6. At Attenuation of 10db, adjust Phase for a local maximum in Diode current.

7. Verify critical coupling by changing attenuation from 10-50. There should be very little change in Diode current.

Data Acquisition

1. Select File/New to create a new spectrum window.

2. If you have parameters stored for a similar sample, select File/Load to load the parameters.

3. If you have no idea what parameters are needed, select Parameters/Experiment to load default parameters. Center field for g=2.00 is 3350gauss if VT unit is installed, 3500gauss if VT is not installed.

4. To add a comment to the parameters, select Parameter/Comment from menu.

5. Select Acquisition/Start… from menu or button from toolbar to start acquisition.

6. Adjust parameters if needed and scan again. Increasing Modulation Amplitude and Time constant will improve signal to noise, but Mod Amp must be small compared to linewidth, and Time Const small compared to time to sweep through peak.

Manipulating displayed spectrum

1. Use View/Scaling, or arrow buttons to move, zoom

2. Use Processing menu to integrate.

3. Additional processing options are available in the WinEPR software package.

Saving Data

1. Select File/Save from the menu. All data should be saved in C:\WinEPR\Data\<User>, where <user> is first initial, last name. Two files will be created, *.spc for spectrum, *.par for parameters.

2. Spectra can also be saved in ASCII format for exporting to Excel or other software packages.

Plotting Spectra

1. Select Parameter/Comment from menu. Enter operator and sample information

2. Select File/Output Formatting from menu. Choose Spectrum or Spectrum + Parameters

3. Select File/Print from menu.

Exporting Data

1. To save a spectrum as a text file select File/Save as, then select type ASCII Spectrum.

2. To copy a spectrum graphic to another application, select File/Copy from menu, then paste to other application.

3. To print spectrum as a .pdf file, select File/Print, then select PrimoPDF as the printer type.

Variable Temperature Operation

1. Check that the nitrogen gas tank is on and set to 40psi, and that liquid nitrogen dewar is at least half full.

2. CAUTION- The various parts of the VT system are very fragile, and very expensive to replace.

3. The Temperature Controller should be turned on before the acquisition software is started.

4. Select Parameter/Temperature Unit Control from the menu.

5. Set Gas Flow to 270, Enter desired temperature, Set Heater and Evaporator Heater to ON.

6. Set Evaporator Power based on temperature.

Temp Power

120-150.1 50%

150-200.1 30-40%

200-300.1 10-20%

>300 OFF

7. Close the Temperature Control Window.

8. Before starting data acquisition, verify that the temperature in the experiment parameters is set to the desired value.

Turn Off Sequence

1. Turn off Magnet Power supply.

2. Exit EPR Acquisition program. Turn off computer.

3. Turn off Electronics. Switch is on back, lower left.

4. Turn off Heat Exchanger. Switch is on front, upper right.

7. Turn off cooling water by turning valve handles perpendicular to pipes.

File Format

1. All spectra are saved as two separate files

*.par A plain text file containing all parameters.

*.spc A binary file containing actual spectra.

Revised 01/09/2014 D. Wilbur