By M Paciolla on Tuesday, February 15, 2000 - 02:19 pm:
I'm using an HP 1100 w/DAD. MP is Buffer-THF (90:10). Buffer is 0.1M KH2PO4 pH 2.7. Flow is 1.0 mL/min and I am using a Cyano column. My sample diluent IS the mobile phase. I observe negative peaks between my first two components. Can anyone give insight on why this is?
By Beppe on Tuesday, February 15, 2000 - 11:15 pm:
Can you see the same negative peaks when you inject your sample diluent alone?
Does you sample (before dilution) contain any other solvent?
These are the two most likely causes for negative peaks.
By Anonymous on Wednesday, February 16, 2000 - 06:04 am:
Quality of THF can also be one of the reasons of negative peak.Change the brand and then check whether negative peak is still coming.
By Andre on Wednesday, February 16, 2000 - 08:44 pm:
What is k’ for your first peak? Is it less than 1?
Yes > change conditions to move away form the column volume.
No > it could be in the sample
Did you try to inject just the mobile phase alone; was there a negative peak?
Yes > check the question below
No > it is in the sample
Do you degas the mobile phase?
Yes > the difference in the amount of dissolved Oxygen between sample and MP can be the source of a strange peak.
No > it is in the sample
By Anonymous on Thursday, February 17, 2000 - 02:23 am:
What is the backpressure of the column? Sometimes if the backpressure is too high it gives negative peak.
By M Paciolla on Sunday, February 20, 2000 - 06:05 pm:
I want to thank all of you for your suggestions.
I believe it is the THF. The backpressure is fine and the the first peak elutes at approximately 2.8 minutes. The negative peaks increased (more negative) as the sample sat. The same was also true for the mobile phase when that was injected.
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