Any technique in which the specimen is bombarded by a focused beam of (primary) ions (diameter less than 10 µm) and the (secondary) ions ejected from the specimen are detected after passage through a mass spectrometer.
Sources:
PAC, 1979, 51, 2243. 'General aspects of trace analytical methods—IV. Recommendations for nomenclature, standard procedures and reporting of experimental data for surface analysis techniques' on page 2246 (https://doi.org/10.1351/pac197951112243)
PAC, 1983, 55, 2023. 'Nomenclature, symbols and units recommended for in situ microanalysis (Provisional)' on page 2025 (https://doi.org/10.1351/pac198355122023)