Hello,                                             12th June 2008

     I'd like to present some data that I obtained yesterday with our Varian/Finnigan MAT 250.  These values are comparable with data from cylinder N2 that we obtained about ten years ago.

Peak ratios, corrected for backgrounds

N2 isotopes        Liquid N2 boil-off             Cylinder N2         Expected from Natural Abundance

29/28                 7.165 E-3                    7.126 E-3                     7.307 E-3
                    (0.981 x Nat. Abund.)   (0.975 x Nat. Abund.)

30/28                 2.406 E-4                    2.532 E-4                     1.335 E-5
                    (18.02 x Nat. Abund.)    (18.97 x Nat. Abund.)

30/29                 3.358 E-2                    3.553 E-2                      1.827 E-3
                    (18.38 x Nat. Abund.)     (19.45 x Nat. Abund.)


     It looks to me like we have a sizeable contaminant at mass 30.  At the risk of displaying our ignorance, might others have noticed similar, unexpected increases at mass 30 from liquid and cylinder nitrogen?  We are thinking to use FTMS to resolve what the contaminant might be (perhaps nitric oxide?), but as yet have not had opportunity to run the FTMS spectrum.


                                            Thank you, Frank Simpson


School of Pharmacy
Univ. Wisconsin
Madison, Wisconsin
tel: 1-608-265-2264
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