The primary scintillation signal in gaseous detectors can be used to obtain the initial interaction time of a detected event, but existing results in the literature for its yield in gaseous xenon are scarce and there is not a good agreement between them. In this work, a standard Gas Proportional Scintillation Counter (GPSC) was used to measure the absolute primary scintillation yield of gaseous xenon at 800 Torr for 5.9 keV X-rays, in order to try to clarify its value. The experimental determination was carried out using the ratio between the primary and secondary scintillation signals. The detection efficiencies of both signals were determined by Monte Carlo simulation results were used to correct the measured ratios. A primary scintillation yield of 73.4 ± 8.8 photons by 5.9 keV X-ray was obtained, from which a wp-value, i.e, the average energy necessary to produce a primary scintillation photon in xenon, of 80 ± 12 eV was obtained. Also, in the same conditions, the primary scintillation was studied in Xenon-Trimethylamine (TMA – (CH3)3N), mixtures with TMA fraction between 0.1% and 1.0%. The primary scintillation signal was only observable at the lowest TMA fraction in the mixture (0.1%). For higher fractions, the primary scintillation signal was not observable, indicating that these may not be suitable mixtures for experiments that use the primary scintillation signal.