The Cation Mass Spectrometer (CMS) has been developed in our laboratory to perform quantitative measurements with an optimal sensitivity and excellent depth and lateral resolution. For positive secondary ions, the MCsx+ mode has been used to circumvent the problems linked to the matrix effect by decoupling the Cs surface concentration from the sputtering conditions, so that an optimal Cs surface concentration is guaranteed and permits one to obtain high sensitivity. Similarly, flooding the sample surface with Cs lowers the work function and permits high useful yields for negative secondary ions. To obtain these performances, a patented neutral Cs deposition column is used for Cs surface concentration control in combination with a surface ionisation Cs+ gun for the sputtering of depth profiles or a Ga+ LMIS for imaging. (C) 2004 Elsevier B.V. All rights reserved.