INDUCED PLASMA MASS SPECTROGRAPH

PURPOSE:To lengthen the life of a detector in an induced plasma mass spectrograph, to widen the measuring range of highly concentrated impurity and to provide an inexpensive detecting system by changing the quantity of ions entered into the detector with the concentration of each of impurities measured so as to count the ions. CONSTITUTION:A perforated auxiliary electrode 30 which directs ions passing through a mass filter 10 to a detector 13 is arranged between the axis of the filter 10 and the detector 13, and a means which impresses voltages respectively upon a repeller 12 and the auxiliary electrode 30 is arranged to change voltage difference between the repeller 12 and the electrode 30 with the concentration of each of impurities measured. Also when the concentration of the impurity measured is high, potential difference between the repeller 12 and the auxiliary electrode 30 is increased more than that set when the low concentrated impurity was measured. This structure can lengthen the life of the detector 13, increase the measuring range of the highly concentrated impurity to that of about six figures and also provide an inexpensive detecting system.