Elemental analysis by Fast Atom Bombardment - Mass Spectrometry (FAB-MS) of biological and food samples has been used by several authors. However, the emission processes in FAB-MS in inorganic analysis have not yet been thoroughly investigated. In the present work, we have studied the effect of the probe material on the positive ion emission of elements found in different matrices, the probe materials that we have investigated are aluminum, gold, graphite and vitreous carbon. The nature of the probe material has a strong effect on the ion emission of several analytes. A vitreous carbon probe was found to provide the strongest analytical signal, its surface has a low porosity and therefore it can be easily cleaned for trace element determination. The composition of the sample matrix also has a strong effect on the analyte ion emission. A high concentration of proteins or of sodium suppresses the analyte signal. We have examined different modifications of the biological matrix to improve the analyte signal.