CAESR

ESR Facility - Department of Chemistry

Concentration / quantity 

As a rule of thumb, a desirable concentration of paramagnetic centres is around 5 mM for frozen solutions, powdered samples, or for solutions of paramagnetic molecules with fast relaxation rates (e.g. transition metal complexes). The quantity required is approximately 50 μL or less, see EPR tubes below for filling heights and tube diameters. For the measurement of organic radicals in solution the concentration needed for the best resolution will be usually much less, c.a. 0.1 mM. 

EPR tubes 

The centre provides an extensive range of EPR tubes suitable for the two EPR spectrometers. You MUST record (in the EPR record book) and pay for the tubes out of your grant. You are strongly encouraged to re-use in particular the high precision EPR tubes, and cleaning facilities are provided in the Sample Preparation Laboratory. There is equipment for sealing all EPR tubes on the vacuum line so that air sensitive samples can be prepared at X- and W-band microwave frequencies. The EPR sample tube and sample volume depends upon the resonator to be used. 

Table: Range of EPR tube diameters (OD, ID) and lengths (L).  5mm NMR tubes don't fit any of the cryostats

Tube Dimensions
  OD          ID           L
(mm)      (mm)     (mm)
 

Microwave

Band

Comment

0.4

0.3

100

 

W

For lossy samples

0.84

0.6

100

 

W

General, for powders and frozen solutions

0.87

0.7

100

 

W

For weak signals. The thin wall makes them unsuitable for solutions that expand when frozen or thawed.

3

-

150

 
  

X

For split ring resonator

3.8±0.013

2.79±0.013

150

 
  

X

For ENDOR pulsed resonator, high precision wall thickness

4

3

250

 

X

For all CW resonators, and the dielectric resonator with 5mm sample access