Component faster than dead volume

[cromatoloco]

I have a peak just at left of my dead volume.
In my standards this component interfer with the peak of dead volume. But in the sample is worst the interference. My blank have the same peak (same rt and abs value)

Is it possible? this component travel faster than my dead volume? or the dispersion of this component is faster from the exit of the column untill the detector? I do not know if someone have had the same problem?

[Andy Alpert]

This implies that there is electrostatic repulsion between this fast-eluting compound and your stationary phase. That would exclude it from a significant percentage of the pore volume. What kind of column are you using and what is the mobile phase? Also, what is the solvent that your sample is in when it's injected?

[Gerhard Kratz]

Or the MW is bigger than the Maximum MW (exclusion Limit) on your column. Anyhow, we Need more Details like mobile Phase, in what is your sample dissolved, what column etc.! Thanks in advance.

[cromatoloco]

Mobile phase: buffer K2HPO4 pH 7.5 : MeOH :: 70:30
Diluent: MeOH
Column: Zorbax, C18, 3.5 um, 4.5 x 150 mm.

[Gerhard Kratz]

What you see is probably an RI effect in the detector cell coming from MeOH. Can you dissolve your sample in Mobile Phase? Or just inject Mobile Phase and your Peak is gone. Inject MeOH 100% and your "Peak" is back again.

[cromatoloco]

Mobile phase: buffer K2HPO4 pH 7.5 : MeOH :: 70:30
Diluent: MeOH
Column: Zorbax, C18, 3.5 um, 4.5 x 150 mm.

Correction:
Mobile phase: buffer K2HPO4 pH 7.5 : MeOH :: 20:80
Column: Zorbax, SB C18, 3.5 um, 4.6 x 150 mm.

[cromatoloco]

What you see is probably an RI effect in the detector cell coming from MeOH. Can you dissolve your sample in Mobile Phase? Or just inject Mobile Phase and your Peak is gone. Inject MeOH 100% and your "Peak" is back again.

My blank is MeOH and I can see the peak. I will try with the Mobile Phase, but the method was developed with MeOH as diluent. If I do that I will eliminate the first peak of dead volume but, why the component is not retained with the column? I need to change the column or add MeOH in the mobile phase?

[Gerhard Kratz]

What is the wavelength you messure?
When you see the "Peak" by injecting 100% Methanol it is not a compound, it is a Change in Refractive Index in your detector cell.
If it is a compound, than I would recommend to use a HILIC column.

[tom jupille]

As has been pointed out, there is a very good chance that what you are seeing is, in fact, "t0 noise" and that it is eluting at (one of) the dead volume(s). The fact is that the definition of dead volume is a bit vague, and the value depends on how it was measured. See for example these two threads from the Forum archives:
http://www.lcresources.com/discus/messa ... 20040107am
http://www.lcresources.com/discus/messa ... 20041222pm

[Andy Alpert]

Wait a minute: You're using a reversed-phase column and your mobile phase contains 80% MeOH? Is this a standardized method that you are attempting to reproduce, or did you develop this combination yourself?