The method of absolute calibration of the TALIF signal of atomic nitrogen by NO titration in the afterglow of a flow tube reactor has been analyzed using TALIF and emission spectroscopy. An increase in production of atomic nitrogen at titration beginning and an asymmetric parabolic curve for emission of NO-beta-bands have been observed. Of three possible explanations of these effects the model of wall recombination was favored: it led to fitted wall recombination coefficients referring to wall loss factors, which where in the same dimension as literature values and was able to simulate a hysteresis effect, which has been observed experimentally. According to the observations the titration end point cannot be used to determine the atomic nitrogen density in the afterglow before any NO has been added into the system as the titer produces part of this density itself. But for absolute calibration purposes referring to the wall recombination model the linear decrease of the TALIF signal with increasing titer concentration can still be used as straight line of calibration. Only a correction of the calibration factor by a factor of 0.59 for 5 mbar titrations has to be taken into account as the titer shows wall interaction not only in a catalytic way, but is partly consumed.