Abstract: For the first time, an intriguing phenomenon was observed in which diisopropyl azodicarboxylate (DIAD) was converted into diisopropyl hydrazine-1,2-dicarboxylate (DIHD) during gas chromatography (GC) analysis. Subsequently, a GC method with pre-column derivatization was developed and validated for the determination of residual DIAD, using triphenylphosphine (TPP) as the derivatization reagent. The method was performed on a gas chromatograph equipped with a flame ionization detector (FID), using direct injection, an Agilent DB-5 capillary column, and a programmed temperature profile. Method validation demonstrated a good linear response for DIAD in the range of 1.057-10.57 µg/mL, with a detection limit of 0.528 µg/mL and a quantification limit of 1.057 µg/mL. The established method allows DIAD and DIHD to be determined collectively as a single analyte, both of which may be introduced during the manufacturing process. It exhibits high accuracy, sensitivity, excellent repeatability and stability, as well as a simple and rapid derivatization procedure. This method is expected to be applicable as a general approach for detecting DIAD and its structural analogues.