We propose a new method for quantifying cobalt oxide on the magnetic recording media using the time-of-flight secondary ion mass spectrometry (TOF-SIMS) technique. Quantification of cobalt oxide using TOF-SIMS can be achieved by the selection of a specific ratio of the mass species Co(OH) to Cr, which is found to represent the characteristics of the corrosive cobalt oxide on the media surface. By setting an appropriate threshold of this ratio at 0.1, the new method correlates very well (correlation coefficient, R² > 90%) with the method using electron spectroscopy for chemical analysis (ESCA), a widely employed surface quantitative tool used to detect magnetic media corrosion. Compared with the ESCA detection limit (at 10% Co_xO_y), it is found that the sensitivity of the new method in detecting the cobalt oxide is much higher with an ability to detect disk media corrosion as low as a ratio of 0.02. This is in stark contrast to the ESCA method which can only detect a change in the disk media corrosion at a much higher limiting threshold at a ratio of 0.1.