I want to make a sample for proton NMR signal-to-noise-ratio measurement. It is conventional to use 1% ethylbenzene in d-chloroform, as specified here.

I have two questions:

  1. What is meant exactly, by 1% ethylbenzene? In some places, I see the notation (v/v), which I take to mean 1% by volume. However, I am still not clear what this means. Does it mean that an amount of ethylbenzene should be used that would fill 1% of the final volume when the solvent is not present? Or does it mean to fill 99% of the final volume with the solvent and then add ethylbenzene until I reach the total volume? Or something else?

  2. What is a good procedure for making such a solution? I imagine a volumetric flask would be useful, but should the solute be measured out by weight? Or using a pipette? I only need about 10 mL of the final solution.

  • $\begingroup$ 10 ml of final solution by 1% v/v should contain 0.1 ml Ethyl benzene. $\endgroup$ May 19 at 17:40
  • $\begingroup$ My personal opinion is that it's better measure out the solute by weight, because common lab weight machines have more precision (4 decimal places i.e. 0.0001 g) than common pipettes (~0.1 mL) $\endgroup$
    – S R Maiti
    May 19 at 21:15
  • $\begingroup$ Ask the manufacturer for a standard suitable for the experiment and spectral range in mind (example) or a befriended NMR group because eventually, these are flame sealed (no evaporation of the solvent across the cap). I saw strychnine in multiple places (equally to anticipate the time of recording necessary) to run a test according to ASTM E2977 and the MNova program. $\endgroup$
    – Buttonwood
    May 19 at 21:24
  • $\begingroup$ It is often much easier to buy these standards - most major chemical/NMR suppliers have them. Note also that the S/N standards are field dependent: a 1% EB standard is for lower fields (<300MHz by memory). Higher fields use 0.1%EB. The preparation of such standards follows the same protocols as for the preparation of any quantitative solution, but it is always easier to make them on a larger scale and only use the volume you need. $\endgroup$
    – long
    May 19 at 21:59
  • 1
    $\begingroup$ Toluene <—> Ethylbenzene. This sounds like a good idea, to measure the mass change of a small syringe rather than the mass change of the flask. I don’t understand why the standard is not specified by molarity. It would give the same result but one would not have to know the density of the solute. $\endgroup$
    – 10ppb
    May 20 at 13:51

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