Chromatography Forum

Hi everybody,
I am using an ODS2 column 5um 250*4.6 mm since last year. I noticed that I get a dip (negative peak) at about 1.26 min. However, in the manufacturer column test the void time was 2.00 min based on Uracil retention time.

Can I use the negative peak I got as the void time?
Does the void time change with the column age?


Thank you in advance

What flow rate?

Flow rate was 1.5 ml/min

It depends on what you need to void time for. If it is of no relevance for anything that you are doing for real, you could use an undefined peak. If you do some proper calculations (for example retention factors) based on a void peak, this void peak should be well defined.

Your strange peak shows up at near the excluded volume of the column.

Thank you Uwe,
I am going to use the void time ( actually void volume) in a method development software to predict the separation of a mixture of several compounds, so I think I will need to define it accurately.

Sorry, do you mean by the excluded volume the void volume?

Next question: what was the flow rate in the manufacturer's test? If they ran at 1 mL/min and you ran at 1.5 mL/min, then their 2 min dead time would drop to about 1.3 min.

Thank you Tom.
They ran the test at 1.0 ml/min so I think the two values are colse enough.

Thank you all

Yes, I did mean excluded volume and not void volume.

Thank you Uwe.
What is the difference between the two?

The excluded volume, also called insterstitial volume, is the volume between the particle. The column void volume is all the liquid volume inside the column, including the pore volume.

Many thanks for all of you .