Investigation of the Matrix Effect of Mg, Si, Ca, Sc, Fe, Y, La and Lu in Pyroxene Composition Synthetic Silicate Glasses by Ion Microprobe

The dependence of the count rate of singly charged secondary ions of the elements Mg, Si, Ca, Sc, Fe, Y, La and Lu on the bulk composition of the sample (known as the matrix effect) was systematically investigated for synthetic silicate glasses using a Cameca IMS 3f ion microprobe. Matrix elements in these samples, with the composition of a Mg-Fe-Ca pyroxene, comprised Mg, Si, Ca and Fe to which were added the minor elements Sc, Y, La and Lu (each at 0.1 atom %). The matrix dependence of all elements was determined quantitatively by ratioing their count rate response to the Ca or Fe yields of the sample. Measurements were conducted using four energy offsets: 0 eV, 40 eV, 80 eV and 120 eV (each 20 eV) with primary beam currents of between 0.5 and 3 nA. For the four minor elements investigated, a non-linear dependence of the absolute sensitivity factors on the Fe content was found at all the energy ranges studied. This matrix effect decreased with increasing secondary ion energy. For the major elements Mg, Si, Ca and Fe, linear as well as non-linear dependences of the absolute sensitivity factors on the Fe content were found, depending on the element and the energy level considered. Because of their importance in the geosciences, relative sensitivity factors of the elements under study relative to Si as reference element (in some cases also relative to Mg) were determined. For low energy ions, a Fe-dependent matrix effect also occurred. For Mg, Y, La and Lu, the matrix effect vanished for some values of the secondary ions energy range.