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ISOGEOCHEM  March 2016

ISOGEOCHEM March 2016

Subject:

Re: Only the first sample peak

From:

Travis Horton <[log in to unmask]>

Reply-To:

Stable Isotope Geochemistry <[log in to unmask]>

Date:

Mon, 14 Mar 2016 20:20:57 +0000

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (84 lines)

Hi Raquel, 

Try switching the two needles at the GasBench bulkhead fittings (i.e. swap your flushing needle for your aquisition/sampling needle).  This will allow you to determine if it's a needle problem or a 'carrier He' feeding the aquisition/sampling needle problem.

Hope this helps!

Travis
________________________________________
From: Stable Isotope Geochemistry [[log in to unmask]] on behalf of Mihai Lefticariu [[log in to unmask]]
Sent: Tuesday, March 15, 2016 9:17 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Only the first sample peak

Raquel,

If you see just the first sample peak when you have only He+0.3% CO2 in the vials then it is possible that carrier He is lost where you connect the sampling line to the gas bench. You can test this by flush/filling manually (gas bench flush/fill lines+vent needles) a few vials with the He+CO2 mixture; overpressurize the vials a little. If you still see just the first sample peak and no indication of leaky vials then the mentioned connection is leaking. Cheers. Mihai


Dr. Mihai Lefticariu
IRMS Scientist
Mass Spectrometry Facility
Neckers 103
Southern Illinois University Carbondale
Carbondale IL 62901

________________________________________
From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of gerard olack <[log in to unmask]>
Sent: Monday, March 14, 2016 12:18 PM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Only the first sample peak

HI Raquel--

Just to make sure, you're testing a tube flushed with a 0.3% CO2 in He
gas mixture, and what you refer to as a  standard on/off, is sequential
sampling--that is the valve switches between sampling loading and sample
injecting, basically filling up the sampling loop and then switching the
valve so the sample in the loop in pushed thru the GC and to the open split.

1.  Is the sampling needle inserted into the vial through out the run?
AS soon as it pulls out, you will stop filling the sample loop.  For
these tests, just stick the needle into the tubes manually, and disable
the autosampler in the sequence line, and start the run (one line at a
time).
2. What size sampling loop?  I presume the 100 uL one--typically the
standard one installed
3.  What is the timing for the sample loop fill and inject cycles? In
the method, look at the timing.  You should see a series of on the off
settings for the switching valve, spaced around 40 to 60 seconds apart.
4.  While you're looking at the timing, make sure the dilution is not
turned on.
5.  Also in your method, first tab I think, you can set an
autodilution.  Basically, if a peak is above the set cutoff, the
dilution will be turned on automatically.  Make sure that is something
high, like 25000 mV.

I hope this helps.

take care,

gerry

On 3/14/2016 8:33 AM, Raquel Mingote wrote:
> Dear All,
>
> We have a Delta V Advantage with GasBench II. The system is not working appropriately. The standard on/off test (test mixture of 0.3% CO2 in He) shows only the first sample peak. Sequential acquisition using the same vial shows only the first sample peak again, in this case with intensity about 23% of the first acquisition. This suggests that there are gas in the vial for analysis. In condition test performed using both the needle of the flush and the acquisition into the sample vial to gently flush the sample line with a 0.3% CO2 in He mixture, all ten sample peaks are shown in the chromatogram.  What should we do? We are newbies in IRMS, so any orientation for this question will be appreciated.
>
> Thanks in advance.
>
>
> Raquel Mingote
>
> Centro de Desenvolvimento da Tecnologia Nuclear - CDTN/CNEN
> Brazil
>
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