River,
Or let your samples go through certain cleanup steps before
sample injection? I mean your samples might have some high molecular steroids
that can hardly evaporate even at your highest GC bake out temperature.
Yi Wang (Ph.D.)
Director, Isotope Laboratory
ZymaX Forensics
600 S. Andreasen Drive, suite B
Escondido, CA 92029
Email: [log in to unmask]
Tel: 760-781-3338 ext 43
Fax: 760-781-3339
Cell: 609-721-2843
From: Stable Isotope
Geochemistry [mailto:[log in to unmask]] On Behalf Of Herbert
Tobias
Sent: Tuesday, October 13, 2009 5:27 PM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] GC-C-IRMS issue
River,
We run underivatized steroids at Cornell University as well. My
experience is that if the column seems to work initially, it's the inlet liner
and septum. You need to change the liner and septum every day. The
other thing to do is make sure you have at least a few minutes of the
temperature program of each run at the highest bakeout temperature. If
you don't continually bakeout the column, you'll get the problems you describe.
cheers,
-Herb
On Tue, Oct 13, 2009 at 8:09 PM, River He <[log in to unmask]> wrote:
Dr. Meier-Augenstein,
I forgot to mention that we used to use guard column at the front end of GC
column. But it seems to us that this doesn't really protect the GC
column, as we still see the similar chromatograph problem with such guard
column.
River
--- On Tue, 10/13/09, Wolfram Meier-Augenstein <[log in to unmask]>
wrote:
> From: Wolfram Meier-Augenstein <[log in to unmask]>
> Subject: Re: [ISOGEOCHEM] GC-C-IRMS issue
> To: [log in to unmask]
> Received: Tuesday, October 13, 2009, 2:55 AM
> Dear River He,
>
>
> Do you run the steroids underiviatized or derivatized? If
> yes to the
> latter, what derivatisation do you use?
>
> Also, do you use a retention gap (= 1 m deactived FS
> capillary between
> injector and column)?
>
> How do you inject; split or splitless?
>
> Lastly, have you checked your column/s after initial
> conditioning for
> active sites by running a Grob test? Similarly, do you
> check yor
> column/s one the problem starts to manifest itself with a
> Grob test run?
> An alkane test will tell you next to nothing if a column
> has developed
> active sites since active sites predominantly affect only
> polar
> compounds.
>
>
> Best,
>
> Wolfram
>
>
> ****************************
> Dr W Meier-Augenstein, CChem, FRSC
>
> Extension: 2624
> E-mail: [log in to unmask]
> URL: http://www.scri.ac.uk/staff/wolframmeieraugenstein
>
> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]]
> On
> Behalf Of River He
> Sent: 13 October 2009 07:45
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] GC-C-IRMS issue
>
> Dear All,
>
> I am posing this note to ask any suggestion and advice
> about the
> problems we have been struggling with our GC-C-IRMS for
> quite a while.
> In fact, we are a little confused.
>
> In our lab, we have a Thermo GC-C-IRMS (Delta V Plus) for
> d13C analysis
> of steroids. Since we bought this system, we have begun to
> deal with the
> chromatograph problem; the tailing of sample peaks.
> Normally after
> putting on a new GC column, the first few batches are fine,
> especially
> the first one or two. BUT very quickly, the chromatograph
> of samples
> deteriorates; the tailing gradually shows up and gets worse
> and worse at
> very fast rate, and after few weeks, the tailing is so bad
> that we
> cannot analyze any sample without changing a new column.
>
> System ontamination by sample was easily considered a
> primary cause, as
> once a while we do see "dirty" samples with high CO2
> background. Cutting
> column, cleaning injector and changing liner or septa
> barely work for
> us(well only worked for once or twice probably). In
> fact, we do
> routinely cut column, change septa, liner and condition
> column. Then, we
> also thought the column may decay due to leaking or
> moisture from the
> samples. Keeping this in mind, in the last few months, we
> had closely
> monitored these two factors and it seems to us that they
> are not the
> reasons either. The Ar background of our system at straight
> mode is
> alway at the level of 80 mV with oven temperature at 60 C
> and its
> reading only increases 20 to 30 mV at the temperature of
> 310 C.
>
> Another thing we observed also kind of confuses us more.
> Although the
> chromatographs of our steroids samples are very poor with
> huge tailing,
> but we can get pretty decent peaks when we run mixture of
> alkanes. This
> tells us that the column seems okay. I am not sure
> whether the
> oxidation tube is a problem. The current one is
> relatively new and we
> just changed it in August. Also, we regenerate
> oxidation tube for at
> least one hour between batches and do this at least
> overnight during
> weekend.
>
> We will greatly appreciate if anyone can give us suggestion
> and advice
> to cope with our problems. BTW, the GC colum
> wecurrently use is
> DB-17MS.
>
> THanks in advnace,
>
> River He
> SMRTL, USA
>
>
>
> __________________________________________________________________
> Yahoo! Canada Toolbar: Search from anywhere on the web, and
> bookmark
> your favourite sites. Download it now http://ca.toolbar.yahoo.com.
>
> ______________________________________________________________________
> This email has been scanned by the MessageLabs Email
> Security System.
> For more information please visit http://www.messagelabs.com/email
> ______________________________________________________________________
>
> ______________________________________________________
> SCRI, Invergowrie, Dundee, DD2 5DA.
> The Scottish Crop Research Institute is a charitable
> company limited by guarantee.
> Registered in Scotland No: SC 29367.
> Recognised by the Inland Revenue as a Scottish Charity No:
> SC 006662.
>
>
> DISCLAIMER:
>
> This email is from the Scottish Crop Research Institute,
> but the views expressed by the sender are not necessarily
> the views of SCRI and its subsidiaries. This email and
> any files transmitted with it are confidential to the
> intended recipient at the e-mail address to which it has
> been addressed. It may not be disclosed or used by any
> other than that
> addressee.
> If you are not the intended recipient you are requested to
> preserve this confidentiality and you must not use,
> disclose, copy, print or rely on this e-mail in any way.
> Please notify [log in to unmask]
> quoting the name of the sender and delete the email from
> your system.
>
> Although SCRI has taken reasonable precautions to ensure no
> viruses are present in this email, neither the Institute nor
> the sender accepts any responsibility for any viruses, and
> it is your responsibility to scan the email and the
> attachments (if any).
> ______________________________________________________
>
__________________________________________________________________
Make your browsing faster, safer, and easier with the new
Internet Explorer® 8. Optimized for Yahoo! Get it Now for Free! at http://downloads.yahoo.com/ca/internetexplorer/
--
Herbert J. Tobias
Cornell University
Ithaca NY 14853
1-607-255-9009 (Lab)