Print

Print


HI Jordon--


You'll need a better GC column, as Ben said.


If you have a large N2 peak, dilute it or, if possible, cut it out.  
Why?  As Libby mentioned, you can form NOx's in the source--and they 
tend to take time to pump out.  That gives you m/z 30 interference that 
varies with N2 signal and a  m/z 30 baseline that changes over time.  
When I tried nitrates on the TC/EA (different system, same principle), I 
needed to dilute the N2 peak to get reliable readings off of CO.


take care,

gerry


On 7/2/2019 10:52 AM, Munizzi, Jordon wrote:
>
> Libby,
>
>
> Sorry in advance if I’m being dense, but how would you exclude the N2 
> from the IRMS (using 100% sample dilution) if N2 and CO are co-eluting 
> from the EA? I understand the issue of mass 30 interference from NO, 
> but to me (with all of two years of real-world experience under my 
> belt J) this seems like a predominantly chromatographic issue.
>
>
> Reporting live from peak 1 of the Dunning-Kruger curve,
>
> Jordon
>
> ----------------------------
>
> *Jordon Munizzi, PhD*
>
> *Research Facility Manager*
>
>
> **Department of Earth and Environmental Sciences**
>
> *University of Kentucky*
>
> Ph: (859) 270-9177
>
> Fax: (859) 323-1938
>
> [log in to unmask]
>
> isotopes.as.uky.edu <https://isotopes.as.uky.edu>
>
> ------------------------------------------------------------------------
> *From:* Stable Isotope Geochemistry <[log in to unmask]> on 
> behalf of Libby Stern <[log in to unmask]>
> *Sent:* Tuesday, July 2, 2019 10:56:46 AM
> *To:* [log in to unmask]
> *Subject:* Re: [ISOGEOCHEM] N2 / CO separation
> Hello Dmitry,
>
> There are a number of paper which discuss this issue (Werner et al. 
> 1996, Farquar et al. 1997, Werner andBrand 2001; Bohlke et al. 2003; 
> Gehre and Stauch 2003; Accoe et al. 2008, Brand et al. 2009; Qiet al. 
> 2011, Hunsinger and Stern 2012).
>
> The N2, forms NO in the ion source and creates a persistent high mass 
> 30 background, adversely affecting d18O measurements.  You have a 
> Conflo IV, which permits 100% dilution/exclusion of the N2 from the 
> ion source, so you should add that 100 % dilution to you method. The 
> addition of a longer column or lower temperature can improve the 
> separation, but that will just improve the post-dilution baseline.
>
> Libby Stern
>
>
>
> On Tue, Jul 2, 2019 at 9:57 AM Dmitry Kopylov <[log in to unmask] 
> <mailto:[log in to unmask]>> wrote:
>
>     Dear all,
>
>     I'm trying to arrange the measurement of d18O in N-containing
>     organics (in hair).
>     The problem is this substance gives a large N2 peak which is
>     registered on the same collectors with CO. The N2 peak stays so
>     close to CO peak that it leaves no time for correct background
>     detection and leads to big errors in d18O measurement.
>     I have tried to decrease the reactor and column temperatures, to
>     increase the start slope / end slope settings, to burn the column
>     at 190 C for several hours. It helps a little, but doesn't solve
>     the problem completely.
>     Does anybody know the ways to improve the separation of these two
>     peaks?
>     Maybe there is a possibility to use another type of column? In the
>     Thermo catalogue there is only one type of column for d18O
>     analysis, but possibly there are other options?
>     I'm attaching the example of spectrum acquired with method: 1450 /
>     60 (Furnace / Oven temp.), 100 / 100 (Carrier and Reference flows).
>     My equipment is DeltaV Advantage + ConFlo IV + EA Isolink Flash IRMS.
>
>     Will be wery grateful for your advices!
>
>     Best wishes,
>     Dmitry Kopylov
>
>     image.png
>
>
>
> -- 
> Libby Stern
> 703-732-7176