IMPROVING THE REPEATABILITY OF REPLICATE ANALYSES IN THE LASER MASS-SPECTROSCOPY OF POWDERED GEOLOGICAL TEST SAMPLES

During laser mass-spectroscopic analysis of powdered geological test s amples, the conditions of ion formation vary because the optical units of the source focusing the laser beam onto the test sample become dus ty. These variations result in the inadequate repeatability of replica te measurements at different exposures. It is shown that the change in the total number of ions generated changes the shape of the mass-cali bration curve of a mass spectrometer, which is among the reasons for v ariations in the analytical signals of elements in the course of analy sis. A technique proposed for the consideration of such ion discrimina tions is based on the concept of the predominant effect of a scattered magnetic field on their formation. The technique was tested in a set of twelve analyses of the International Geological Standard W-2 (diaba se). With the use of this technique, the relative standard deviation w as decreased several times to 13% averaged over 30 elements.