Metaphosphate glasses such as LiPO3 and NaPO3 are known to incorporate nitrogen in the molten state under NH3 flow to form (Li/Na)PON glasses through the reaction: (Li/Na)PO3 + xNH3 → (Li/Na)PO3−(3x/2)Nx + (3x/2)H2O, by partially replacing two‐coordinated oxygen with two‐ and three‐coordinated nitrogen. After nitridation, the glasses exhibit improved properties such as increased working range, chemical durability, and ionic conductivity. In this study, LiPO3 and NaPO3 glasses were prepared by the conventional melting and casting method and used as base glasses for the ammonolysis procedure. The nitridation processes were carried out by remelting the base glasses at temperatures up to 780°C, under a constant NH3 flow. The effects on the nitrogen content in the resulting (Li/Na)PON glasses caused by different processing times and masses of powder and/or bulk materials were investigated. Nitridation was successfully confirmed by CNHS chemical analyses, Raman spectroscopy, and Differential Scanning Calorimetry. Mass loss measurements after the ammonolysis process and Raman spectroscopy were used to quantify the nitrogen content into the glass structure. A new approach using a specific Raman normalization, (P–N<)/(O–P–O)sym, has been demonstrated as a reliable, simple, and fast way to determine the amounts of N incorporated to metaphosphate glass structures.