Abstract <p>The impurity composition of isotopically enriched tetrakis(trifluorophosphine) nickel ⁵⁸Ni(PF₃)₄ was studied for the first time using the gas chromatography-mass-spectrometry. The possibilities of using GS-GasPro 60 m × 0.32 mm capillary columns with silica gel as a sorbent and DB-5MS 30 m × 0.32 mm × 0.25 μm with methylsiloxane for the separation of impurities were studied. Impurities were identified by comparing their mass spectra with those known from the literature. Impurities of permanent gases, a number of hydrocarbons from C₁ to C₉, dichloromethane, 1-propene-1-(2-furanyl) and an alkyl derivative of tetrakis(trifluorophosphine)nickel were detected, and their concentrations were determined. Detection limits for impurities at the level of 9 × 10^–5–4 × 10^–6 vol % were achieved. For the first time, the mass spectrum of Ni(PF₃)₃(PF₂CH₃), which is absent from literary sources, was obtained and described.</p>