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Hi Alice,

We run everything from near natural abundance to 99 atom % 15N on our
EA-IRMS. We are an isotope tracer lab so we aren't going for high
precision measurements near natural abundance. That said, after we ran 99
atom % 15N through our instrument, running a couple hundred dummies and
empty wells got us back to natural abundance levels and 0.1 per mil
standard deviation on 5 reps of 2 mg peach leaves. Changing out the
catalysts and drying tubes didn't help as much as just running a lot of
dummies or empty wells. You might space out your samples with one empty
well in-between samples, and then after you are done with your enriched
run, do the 15N cleanse. And of course run a set of standards before you
resume natural abundance work to make sure that you are indeed back at
natural abundance.

Wendy


> hi Alice,
> we usually avoid strongly enriched samples,but there was once an error in
> an experimental setup and we got a few sampleswith ca 2400 permil 15N
> (instead of 240 expected). To my surprise, nothing wrong happened. The
> contamination could be suggested in two or three next samples and then
> everything was completely ok (though I changed the columns soon). These
> were fungal samples of ca 800 mcg in wt; we use Delta V plus and Flash
> 1112.
> There is however another problem: theisotopic signals are not linear and
> one needs to run a standard with d15N close to that in the enriched
> samples for a proper correction. Otherwise the values obtained could not
> be fully reliable.
> All the best, Alexei
>
>
> Wed, 25 May 2011 19:20:29 +0000 письмо от "Chang, Alice"
> <[log in to unmask]>:
>
> Hi all,
>
> Has anyone run really enriched (d15N = ~1000 per mil) samples through
> their EA-IRMS system? In a previous thread (Nov 2009) I had asked about
> how to clean surfaces after using enriched tracers, and someone suggested
> that I not run anything >500 per mil. My student with the 1000 per mil
> samples would like some quick results instead of sending the samples
> elsewhere, and I am just wondering if it's worth running these samples on
> my sole EA that is used for both natural abundance and less-enriched
> samples.
>
> If I were to run these highly enriched samples, what would be the proper
> protocol to prevent carryover to the next sample, and to decontaminate the
> EA-IRMS altogether? Run 5-10 acetanilides in between each sample? Run
> these samples near the end-of-life of the column chemicals? Run an
> autosampler tray full of acetanilides before analysing natural abundance
> samples again? If contamination arises in the connecting tubings, how best
> to clean those?
>
> If I decide not to run these samples on my EA, is there anyone out there
> who can?
>
> Thanks for your thoughts.
> Alice
>
> --
> Alice Chang
> Stable Isotope Facility
> Department of Forest Sciences
> University of British Columbia
> Vancouver, BC, Canada
> phone: 604-822-3047
>
> **********************************
> Dr. Alexei V. Tiunov
> Laboratory of Soil Zoology
> Institute of Ecology and Evolution
> Leninsky pr. 33
> 119071 Moscow, Russia
> Tel. +7 495 958 1449
> Fax. +7 495 954 5534
>
>


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Wendy H. Yang, Ph.D.
Post-Doctoral Scholar
Ecosystem Sciences Division
Dept. of Environmental Science, Policy, and Management
137 Mulford Hall, #3114
University of California
Berkeley, CA 94720

Office: 131A Hilgard Hall
Tel: (510) 642-3874
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