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By Bob G on Saturday, July 24, 2004 - 08:05 am:
I am observing decrease in retention time of 20 % in 10 days of using a Dioex AS11 column for IC. I use three columns so far with similar results. My
third column was exposed to anion standards only. I analyse water based samples and this method has worked fine for several years until we cahnge to As11. I use good water, Ultra pure chemicals (50% base - tried new bottle), eluent is filtered with 0.45 micron. My baseline signal is not changing. We switch to As15 and see a lower loss but problem continue. My peak area is good but retention time is decreasing run to run. Earlier method used Transgenomic column and we had no such problem.
Any one has ideas to help above problem.
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By Chris Pohl on Sunday, July 25, 2004 - 03:24 pm:
Bob,
There are several possible causes for this. One possible cause is a contaminant in your water. What is the quality of your DI water? Any chance of bacterial and/or other life forms in your water system?
Another possible cause is silicates due to corrosion of glass bottles. Are you using glass bottles for your eluents? If so, you should switch to polymer based eluent bottles (preferably HDPE, polypropylene or PTFE).
Progressive contamination of your eluent with carbonate is another possibility. How are your eluents protected from the air? Generally it works best if the eluent is pressurized with nitrogen or helium. If this is the problem, the background should slowly increase and fresh eluent should at least partially restore lost retention.
Other possibilities exist but I need more info to cover these cases: eluent (and gradient conditions if you are operating in gradient mode), flow rate, operating temperature, injection volume, specifics of other equipment (pump, valve, end line filter, etc.). For example, the problem could be due to a valve with a vespel rotor if you are using a conventional HPLC as your hardware platform. For basic eluents the wetted surfaces in the valve should be PEEK or Tefzel.
I am observing decrease in retention time of 20 % in 10 days of using a Dioex AS11 column for IC. I use three columns so far with similar results. My
third column was exposed to anion standards only. I analyse water based samples and this method has worked fine for several years until we cahnge to As11. I use good water, Ultra pure chemicals (50% base - tried new bottle), eluent is filtered with 0.45 micron. My baseline signal is not changing. We switch to As15 and see a lower loss but problem continue. My peak area is good but retention time is decreasing run to run. Earlier method used Transgenomic column and we had no such problem.
Any one has ideas to help above problem.
-------------------------------------------------------------------------------------------------------
By Chris Pohl on Sunday, July 25, 2004 - 03:24 pm:
Bob,
There are several possible causes for this. One possible cause is a contaminant in your water. What is the quality of your DI water? Any chance of bacterial and/or other life forms in your water system?
Another possible cause is silicates due to corrosion of glass bottles. Are you using glass bottles for your eluents? If so, you should switch to polymer based eluent bottles (preferably HDPE, polypropylene or PTFE).
Progressive contamination of your eluent with carbonate is another possibility. How are your eluents protected from the air? Generally it works best if the eluent is pressurized with nitrogen or helium. If this is the problem, the background should slowly increase and fresh eluent should at least partially restore lost retention.
Other possibilities exist but I need more info to cover these cases: eluent (and gradient conditions if you are operating in gradient mode), flow rate, operating temperature, injection volume, specifics of other equipment (pump, valve, end line filter, etc.). For example, the problem could be due to a valve with a vespel rotor if you are using a conventional HPLC as your hardware platform. For basic eluents the wetted surfaces in the valve should be PEEK or Tefzel.
