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 samples, the conditions of ion formation vary because the optical units of the source focusing the laser beam onto the test sample become dusty. These variations result in the inadequate repeatability of replicate measurements at different exposures. It is shown that the change in the total number of ions generated changes the shape of the mass-calibration curve of a mass spectrometer, which is among the reasons for variations in the analytical signals of elements in the course of analysis. A technique proposed for the consideration of such ion discriminations 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 (diabase). With the use of this technique, the relative standard deviation was decreased several times to 13% averaged over 30 elements.