1 - Conversion Tables

Conversion tables and other tools to (hopefully) make life easier

Tools

1.1 - Power to Volts Conversion

Power to volts conversion table

System Impedance: 50 Ohm

Variable Description: P (dBm) - Power in dBm, P (mW) - Power in mW, Vrms - RMS voltage, Vpp - Peak-to-peak voltage, Vp - Peak voltage (as measured from GND)

P (dBm) Vrms (V) Vpp (V) Vp (V) P (mW)
30 7.071 20.000 10.000 1000.000
29 6.302 17.825 8.913 794.328
28 5.617 15.887 7.943 630.957
27 5.006 14.159 7.079 501.187
26 4.462 12.619 6.310 398.107
25 3.976 11.247 5.623 316.228
24 3.544 10.024 5.012 251.189
23 3.159 8.934 4.467 199.526
22 2.815 7.962 3.981 158.489
21 2.509 7.096 3.548 125.893
20 2.236 6.325 3.162 100.000
19 1.993 5.637 2.818 79.433
18 1.776 5.024 2.512 63.096
17 1.583 4.477 2.239 50.119
16 1.411 3.991 1.995 39.811
15 1.257 3.557 1.778 31.623
14 1.121 3.170 1.585 25.119
13 0.999 2.825 1.413 19.953
12 0.890 2.518 1.259 15.849
11 0.793 2.244 1.122 12.589
10 0.707 2.000 1.000 10.000
9 0.630 1.783 0.891 7.943
8 0.562 1.589 0.794 6.310
7 0.501 1.416 0.708 5.012
6 0.446 1.262 0.631 3.981
5 0.398 1.125 0.562 3.162
4 0.354 1.002 0.501 2.512
3 0.316 0.893 0.447 1.995
2 0.282 0.796 0.398 1.585
1 0.251 0.710 0.355 1.259
0 0.224 0.632 0.316 1.000
-1 0.199 0.564 0.282 0.794
-2 0.178 0.502 0.251 0.631
-3 0.158 0.448 0.224 0.501
-4 0.141 0.399 0.200 0.398
-5 0.126 0.356 0.178 0.316
-6 0.112 0.317 0.158 0.251
-7 0.100 0.283 0.141 0.200
-8 0.089 0.252 0.126 0.158
-9 0.079 0.224 0.112 0.126
-10 0.071 0.200 0.100 0.100

1.2 - Convesrion: dBm to Power

dBm to power conversion table
P (dBm) P (W) P (dBm) P (W) P (dBm) P(W) P (dBm) P (W)
0 0.0010 10 0.0100 20 0.1000 30 1.0000
1 0.0013 11 0.0130 21 0.1260 31 1.2600
2 0.0016 12 0.0158 22 0.1580 32 1.5800
3 0.0020 13 0.0200 23 0.2000 33 2.0000
4 0.0025 14 0.0251 24 0.2510 34 2.5100
5 0.0032 15 0.0316 25 0.3160 35 3.1600
6 0.0040 16 0.0398 26 0.3980 36 3.9800
7 0.0050 17 0.0501 27 0.5010 37 5.0100
8 0.0063 18 0.0631 28 0.6310 38 6.3100
9 0.0079 19 0.0794 29 0.7940 39 7.9400
40 10.0000

2 - Standard Samples

Preparation instructions for EPR standard samples

2.1 - BDPA in Polystyrene

Preparation of a BDPA in PS sample for EPR Spectroscopy

Warning

These instructions are written for scientists that are trained in handling hazardous chemicals. Please follow general safety guidelines.

General Information

BDPA (α,γ-bisphenylene-β-phenylallyl-benzolate) is a well characterized stable radical, often used as a standard in EPR spectroscopy. The radical is highly stable and one of the first organic, stable radicals ever synthesized [1].

BDPA can be obtained from all major chemical vendors such as Sigma-Aldrich (Milipore Sigma). Typically, BDPA is co-crystallized with benzene in a ratio of 1:1. In the following this complex is referred to as BDPA for simplicity.

Name: α,γ-bisphenylene-β-phenylallyl-benzolate (BDPA)
Empirical Formula: C39H27
CAS Number: 35585-94-5
Molecular Weight: 495.63 g/mol

Usage in EPR Spectroscopy

Neat BDPA Crystals

Neat BDPA can be used in EPR spectroscopy. For example, individual crystals, picked from the bottle make a good standard to observe an FID or if only a small spec of an EPR active substance is required for example to map out the B1 field of a resonator. However, be careful when handling neat BDPA. The smallest contaminations can result in large EPR signals, which will require extensive cleaning.

BDPA Dissolved in Polystyrene

BDPA dissolved in polystyrene (BDPA/PS) makes a stable and very reliable standard sample for EPR spectroscopy at any frequency. BDPA has a very small g-anisotropy, and, unless the sample is prepared from perdeuterated BDPA in fully deuterated polystyrene, the g-tensor asymmetry is not visible at frequencies below 140 GHz.

EPR Properties

Experimentally determined g-values and hyperfine parameters for BDPA are summarized in the table below:

Parameter Values
gxx, gyy, gzz 2.00263, 2.00259, 2.00234
A(1)xx, A(1)yy, A(1)zz (MHz) 0.25, 0.25, 0.27
A(2)xx, A(2)yy, A(2)zz (MHz) 1.18, 0.82, 0.30

The values for the two hyperfine tensors are obtained for deuterium nuclei and scaled to proton frequencies. Values taken from [2].

Sample Preparation

The general procedure to prepare the BDPA/PS sample is as follows:

  1. Prepare two separate solutions of BDPA and polystyrene in toluene.
  2. Mix appropriate aliquots of the BDPA and polystyrene solutions to achieve desired concentration (ratio).
  3. Pour mixture onto clean glass plate and let toluene evaporate at room temperature.
  4. Using a spatula, scrape plastic film off the glass plate
  5. Dry sample material in vacuum

Example – Preparation of a 0.1 % BDPA/PS Sample

For EPR spectroscopy a useful concentration ranges between 0.025 to 0.1 % (w/w) BDPA/PS.

For this preparation, all chemicals are lab grade chemicals and used without further purification.

To prepare a 0.1 % of BDPA in PS follow these steps:

  1. Make BDPA stock solution by dissolving 10 mg BDPA in 1 ml toluene.
  2. In a small beaker dissolve 1 g of polystyrene in a small amount of toluene. Typically, 2 to 3 ml should be sufficient. The more toluene you use, the longer it will take for the toluene to evaporate.
  3. Add 100 µl of the BDPA stock solution to the polystyrene solution for a finale concentration of 0.1 % (w/w) BDPA/PS. To prepare a sample with a lower concentration, adjust the amount of BDPA stock solution that gets added to the polystyrene solution.
  4. Pour the entire solution onto a clean glass plate. Make sure the glass plate is leveled and large enough. If necessary, pour the solution in several small badges.
    • Alternatively, use non-stick aluminum foil such as Reynolds Wrap (non-stick).
  5. Let the toluene evaporate at room temperature in a fume hood. This can take several days. To speed up the process, once the majority of the toluene is evaporated, put the plate into an oven or incubator. Keep the temperature low (35-40ºC). Make sure the area is well vented, toluene is highly flammable.
  6. Once the sample is dry, not gooey or sticky anymore, scrape the sample material off the glass plate using a spatula and transfer the sample material into a small (round-bottom) flask that can be evacuated.
    • Optionally, weigh the empty flask, note down the weight and repeat it once the sample material is transferred into the flask to get the initial weight of the sample material.
  7. Dry the sample in vacuum.
    • Weight the flask throughout the drying process. Once the weight is stable, all toluene has been removed.
  8. Once dry, grind the sample material to a fine powder using a mortar and pestle.

Important

Make sure the sample material is dry and all toluene is removed from the sample. The best way to make sure all toluene is removed is by weighing the sample during while drying the material in vacuum.

If not all toluene is removed, small pockets with high concentrations of BDPA can form. This typically shows up as sharp peaks in the powder spectrum

To avoid the formation of small pockets, make sure to pour a thin layer of the toluene solution onto the glass plate.

Once the sample material is transferred to the EPR tube, the sample can be used as is. However, if all oxygen is removed from the sample the longitudinal relaxation time T1e can be dramatically improved. Typically, an evacuated sample will have a T1e about factor 200 longer compared to a sample exposed to air. To remove the oxygen, evacuate the sample capillary and flush with argon. Repeat this cycle several times. After the last cycle the sample capillary must be flamed sealed. You can do this in two ways:

  • Do not flush the sample with argon after evacuating. That way, the walls of the sample capillary will collapse, once heated by the torch.
  • Flush the sample with argon. Don’t overpressure the sample tube with argon.

Both cases need a bit of practice.

Sample Concentration

Sample (mg) %w g(BDPA) mol(BDPA) Spins/mg
1 1.000 1.00E-05 2.02E-08 1.22E+16
1 0.100 1.00E-06 2.02E-09 1.22E+15
1 0.050 5.00E-07 1.01E-09 6.08E+14
1 0.025 2.50E-07 5.04E-10 3.04E+14
1 0.001 1.00E-08 2.02E-11 1.22E+13

References

  1. C.F. Koelsch, Syntheses with Triarylvinylmagnesium Bromides. α,γ-Bisdiphenylene-β-phenylallyl, a Stable Free Radical, J. Am. Chem. Soc. 79 (1957) 4439–4441. https://pubs.acs.org/doi/10.1021/ja01573a053
  2. V. Weis, M. Bennati, M. Rosay, J.A. Bryant, R.G. Griffin, High-field DNP and ENDOR with a novel multiple-frequency resonance structure, J Magn Reson. 140 (1999) 293–9. https://doi.org/10.1006/jmre.1999.1841.