Hello -
Costech has recommended to me baking out the GC oven at 110C for  
several hours every 3-4 months.
-- 
Charlotte Lehmann
Assistant in Instruction
Bates College
Department of Geology
206A Carnegie Science Building
44 Campus Avenue
Lewiston, ME 04240
Phone: 207-786-6485
FAX: 207-786-8334


Quoting Paul Brooks <[log in to unmask]>:

> Bjoern,
>
> We had similar problems a few years back.  Now we bake the GC column
> overnight very month and replace the column every few years.  They
> definitely do not last for ever.  Ours is a Europa system, and we bake
> the column out at 145C, I don't know what the temperature limit is for
> the Costech one, but I normally bake GC columns out at 25C below their
> maximum temperture.
>
> Good Luck!
>
> Paul Brooks.
>
>
>
> At 09:07 AM 2/14/2008, you wrote:
>> Bjoern:
>>
>> I would concur with the suggestions to bake the column, having had a similar
>> problem with an identical setup. New and stored columns both require this
>> baking, so switching the GC column might not have eleiminated the issues.
>>
>> Check m/z 18; this represents water. If it is high, then that would would
>> indicate that your column needs baking. This is the typical reason   
>> for a high
>> 15N baseline (water reacting with N2 or N on the cathode to form N2O).
>>
>> If this doesn't help, a new GC column is likely the answer; the   
>> delayed peak is
>> idicative of some sort of obstruction in your line or failure/blocking (by
>> water) of the GC column - since you seem to have changed everything  
>>  else that
>> could reduce the flow.
>>
>>
>>
>> Quoting Bjoern Wissel <[log in to unmask]>:
>>
>>> Hi there,
>>>
>>> I have been running basic C+N stable isotope analyses on a Costech EA
>>> connected to a Finnigan Delta plus for a number of years without problems.
>>> Recently, I observed an elevated N2 baseline (30 to 40 mV instead of
>> 15 to 20
>>> mV) in combination with prolonged peak retention times (N2 peak
>> starts at 180
>>> sec instead of the normal 100 sec) and peak durations are longer as well.
>>>
>>> Since then, I checked for leaks (pressure and Ar), changed seals,
>> water trap,
>>> combustion / reduction columns, He tank, GC column, and connection to the
>>> ConFlo but nothing changed the elevated baseline and late peaks. The flow
>>> rate is constant at 120 measured at the outlet of the EA and
>> directly at the
>>> GC column.
>>>
>>> I am wondering if anyone came across this or a similar problem, or does
>>> anyone have any ideas what could cause this phenomenon. I would greatly
>>> appreciate any comments and suggestions.
>>>
>>> Thanks, Bjoern
>>>
>>>
>
> Center for Stable Isotope Biogeochemistry
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