Acetonitrile volume mixing ratios are derived from positive ion spectra obtained with a balloon-borne quadrupole mass spectrometer in an altitude region from 21 to 32 km. Comparison of the results with data obtained in previous flights suggests a larger deviation from reference profiles, probably due to temporal transport phenomena. From negative ion spectra obtained during the same balloon flight, the concentration of sulfuric acid vapour between 22 and 32 km is also deduced. These results seem to be in reasonable agreement with earlier data which were mostly obtained shortly after a period of enhanced volcanic activity.