I received responses from 5 labs with data on NBS 1572 (Citrus Leaves) -
thanks to you all.  For any others who may still be using this material,
here are the the results from this little survey (including my own lab).

Lab#     d13C     d15N
1        -27.33     5.09
2        -27.38     4.04
3        -27.3       4.8
4        -27.21     5.07
5        -27.30     4.58
6        -27         4.7

Mean  -27.26    4.7
Stdev     0.14    0.4

(Lab 6 provided only an approximate value for d13C - when a more precise
number is available, I will update the list and statistics.)

I hope some of you will find this useful - it was certainly very helpful to me.

-Bob



At 02:37 PM 7/14/2003 , you wrote:
>Dear List Members,
>
>I've been using a bottle of NBS 1572 (Citrus Leaves) as a weight-percent
>standard for CN analysis for over 15 years (obviously from before NBS
>became NIST), and as an isotope standard for medium-precision CF-IRMS for
>over 10 years (with a Europa Roboprep/Tracermass).  (Europa provided
>samples of this material with installation of the Tracermass, along with
>"accepted" delta values to use for calibration.)  The isotope values I've
>been using for this material are -26.60 (PDB) for d13C and +5.19 (Air) for
>d15N.  I now have a new Delta+ XP/Costech EA system, and the results I'm
>getting from this instrument are suggesting that my old numbers may be off
>by as much as 1 per mil for both elements.  Does anyone have data for NBS
>1572, or other information that might provide some insight into this
>apparent discrepancy?
>
>Thanks,
>
>-Bob
>
>
>Robert L. Petty, Ph.D.
>Manager, Analytical Laboratory
>Marine Science Institute
>University of California
>Santa Barbara, CA 93106
>Voice (805) 893-3802
>Fax (805) 893-2122