>Dear IsotopeGeochem,
>
>There appears to be two methods to analyze C-13 and N-15 on combustion
>samples with CF-IRMS.  One manufacturer runs the N-15 and then detunes the
>source and runs C-13 at reduced sensitivity (VG), while the second has a
>diluter that dilutes the C-13 with more carrier gas prior to dynamic
>analysis.  Both claim their protocol is superior.  What are the user's
>experience with the two systems, pitfalls and positive points?
>
>Thanks is advance and Happy Holidays,
>
>Bill
>
>William J. Showers
>Dept of Marine Earth & Atm. Sciences,
>North Carolina State Univ.
>
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I am a novice user of a Europa ANCA-SL/2020 analyzer which is a CF-IRMS.
For dual isotope analysis on the same sample, we seperate the N2 and CO2
gases in a GC column and change the source settings inbetween peaks.  This
results in a precision of about 0.5 per mil (standard deviation) for N and
0.1 per mil for C (standard deviation).  These are at natural abundance
levels.  This precision is the WORST precision allowable.  Often times
precision will run about 0.3/0.06 per mil for N and C respectively.
Unfortunatly, I have no experience with the other method.  Hope this helps.



--
Myq  Larson     Stable Isotope Facility 435.797.0060
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