Hi Yi,

Thanks and I just sent Wolfram an email about this.

River

--- On Tue, 10/13/09, Yi Wang <[log in to unmask]> wrote:

> From: Yi Wang <[log in to unmask]>
> Subject: Re: [ISOGEOCHEM] GC-C-IRMS issue
> To: [log in to unmask]
> Received: Tuesday, October 13, 2009, 4:02 PM
> River,
> I have the same questions from Wolfram for you. Steroids or
> polar sample
> matrix underivatized could easily contaminate your GC
> column, which may
> not be indicated by non-polar n-alkanes standard runs. 
> 
> 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
> http://www.zymaxusa.com
> 
> 
> 
> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]]
> On
> Behalf Of Wolfram Meier-Augenstein
> Sent: Monday, October 12, 2009 11:56 PM
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] GC-C-IRMS issue
> 
> 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
> 
> 
>      
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