We report on the generation of an octave-spanning (600-1400 nm) nearly monocycle (1.1 cycle) ultrashort optical pulse (3.2 fs) in the near-infrared region by the Fourier synthesis of two pulses at 800 and 1200 nm, both of which were spectrally broadened by self-phase modulation and were compressed by chirp mirrors. The 3.2 fs pulse was converted into the ultraviolet by third harmonic generation, the pulse width being evaluated to 1.9 fs. The near-infrared pulse (3.2 fs) was employed as an ionization source in mass spectrometry, and the signal intensity was significantly increased for pentachlorobenzene, an environmental pollutant listed in the Stockholm Convention. The present data and the spectral properties obtained by quantum chemical calculations suggest that the method offers a potential advantage for the detection of Novichok, a chemical warfare agent that is thought to have been used in a terrorist attack.