capacitance of the ion source to ground thus the voltage applied to the sample plate v s relative to the voltage v i on the internal charged capacitor is given by where c i is the internal capacitance of the high voltage pulse generator and c s is the capacitance to ground of the sample plate any variation in c s produces a variation in the voltage applied to the sample plate thus changing the magnitude of the acceleration applied to the ions this causes an uncontrolled variation in the performance of the tof mass spectrometer with position of the sample plate affecting in particular the resolving power and accuracy of the mass measurement in some tof analyzer designs it is important to keep the distance between the sample plate and the extraction electrode as small as possible without initiating an electrical discharge the capacitance between the sample plate and the extraction electrode is inversely proportional to the distance between them and directly proportional to the area of the overlap between the electrodes thus if the area is reduced in the same proportion as the distance then the capacitance is independent of the distance between the sample plate and the extraction electrode in one embodiment of the present invention the distance between the sample plate and the extraction electrode is 3 mm and the outer diameter of the electrode is 25 mm with a 1 5 mm aperture in the center of the plate the overall dimension of the sample plate holder with sample plate installed is 133 u00d7 127 mm and the active area where samples may be deposited is 108 u00d7 102 mm with.