Chromatography Forum

Dear all:
I need help in selecting a suitable compound to determine the void volume in a normal phase separation:
The column is YMC-Pack Diol - 120 NP (5 um, 12 nm) 250 x 4.6 mm
The mobile phase Hexane-ethanol (1000+20)
The detection available is UV.

The objective is to select a compound for a practical determination (not theoretical) in normal phase (as uracil or nitrate are used in RP).
I think that acetone could be a suitable compound but I want to know your expert opinion.

Further context: The method is an USP method to determine impurities in Norgestimate (Test 2, 210 nm).
We are undertaking full validation of the method for European authorities because they do not recognize this USP method as validated (I don't know why).
Thank you in advance.

Dear all:
I need help in selecting a suitable compound to determine the void volume in a normal phase separation:
The column is YMC-Pack Diol - 120 NP (5 um, 12 nm) 250 x 4.6 mm
The mobile phase Hexane-ethanol (1000+20)
The detection available is UV.

The objective is to select a compound for a practical determination (not theoretical) in normal phase (as uracil or nitrate are used in RP).
I think that acetone could be a suitable compound but I want to know your expert opinion.

Further context: The method is an USP method to determine impurities in Norgestimate (Test 2, 210 nm).
We are undertaking full validation of the method for European authorities because they do not recognize this USP method as validated (I don't know why).
Thank you in advance.

The void volume is approximately 67% of the column volume. You can check with previous threads in the forum

Thank you haiedc.

I already read some of the numerous interesting entries about this topic written by the generous experts from the Forum.

My goal is to do a practical measurement that would be suitable to two purposes: to calculate k' values and track performance of the chromatographic system over time.

For the first purpose the "rule of thumb" estimations that are based on assumptions about the % of the column volume that is "interstitial" (between the particles) and the % of the column volume that is internal (inside the pores) would be useful, but not for the second.

That why in trying to select a compound for a practical determination (not theoretical) in normal phase

With 2% ethanol in the mobile phase, toluene might work.

You can try as Uwe suggests. For good measure you might also try at 10% ethanol and make sure it is the same as with 2%.

Uwe: I will try as you suggest.
Marc: Your addtional confirmation experiment seems to me a good idea.

Thanks to you all.