We have Delta V Advantage with Flash EA 1112.
During nitrogen measurement, after 80 s, the m/z29 signal in the background begins to grow and drastically changes 29/28 ratio. That very much influences the nitrogen stable isotope value of the sample.
What can cause such m/z29 grow? Reduction column was filled by new copper wires ( 4*0.5 mm) from Elemental Microanalysis.
The 13C measurement are very normal, any deviation.