Decreased in retention time

[maria]

Hi Friends,
I am a new user of Dionex IC system. Recently i have found that there is a drastic decrease in the retention time. For eg. previously if a peak was eluting at 15 min, now the same elutes at 10.5 min. what's the reason? Can u suggest how i can bring it to normal. seeking info. Thanks

[Kostas Petritis]

I would guess that you only need to regenerate your column according the manufactuerers instrunctions. Other reasons could be the room temperature, but I will assume that it does not vary too much...

[Chris Pohl]

Maria,

To answer that question, we need more information:

1). The column

2). The eluent

3). Operating conditions (flow rate, temperature, etc.)

4). The sample (as much information as possible, including known sample components, injection volume, target analytes, etc.)

[maria]

I have already followed the cleanup procedure with 90mM Na2CO3 mobile phase.
My column is AS9-HC,2mm withe ASRS-ULTRA suppressor. I use 9mM Na2CO3 solotion for the determination of anions such as F-, Cl- SO4- in seawater samples. at a flowrate of 0.25ml/min. Loop size is 25ul. I hope this information is sufficient. Thanks

[Chris Pohl]

Maria,

Changes in retention time for this column might well be due to gradual hydrolysis of the ester links attaching the quaternary ion exchange sites to the polymer backbone. Although we designed the stationary phase to be resistant to base hydrolysis, the ester group is ultimately subject to this problem when used under alkaline conditions. How old is this column? What have you been using as the storage solution?

[maria]

i use sodium bicarbonate as a storage solutiom

[Chris Pohl]

Maria,

Since you are using sodium bicarbonate as your storage solution, the cause of your problem is probably not hydrolysis of the ester linkage. The column is quite stable when stored in sodium bicarbonate solution. Perhaps the cause of the problem is related to the sample contamination. What is your sample (major components, sample solvent and injection volume)?

[maria]

I have been using for determination of sulphate in seawater samples after diluting it 100 times. and the loop is 25 ul.

[Chris Pohl]

Maria,

I can't gave you a detailed assessment of the fouling potential of seawater as I have limited experience with this sample matrix. Have you ever attempted to clean the column? If not, I would suggest that you investigate using the cleaning protocol described for removing organic contaminants (the specifics are in the column manual but it consists of potassium nitrate, nitric acid and acetonitrile). It would seem plausible that "lifeforms" would be present and the loss of capacity could potentially be connected to high molecular weight byproducts of such lifeforms. Do you filter your sample before injecting it? This might be advisable when analyzing samples were likely to contain lifeforms.

[widanarti]

Hi all,

Sorry to interupt you... but I have the same problem with Maria, so I think it won't be so out of topic if I ask your help either. I'm new user of HPLC. I use Agilent 1100 and Zorbax Carb column for oligosaccharides separations.

The retention time was decreased and the resolution as well. I use suggested operating conditions in column manual, which are ACN/water as mobile phase, isocratic controlled temperature, RID detector.

Is there any possibilities of column dryness, since I left it for about a month before it happens?