NOTE 1 The use of fused beads generally improves the accuracy of analysis for non-volatile elements, since it eliminates variability arising from differences in mineralogical forms or oxidation states. Pressed pellets generally improve the accuracy of analysis for volatile elements and can give adequate accuracy for the routine analysis of non-volatile elements.
NOTE 2 The presence of sulfide in a sample also leads to restrictions on the scope of the analysis that can be undertaken using the XRF technique based upon fused beads. In particular, sulfate (SO3) cannot be determined directly from such a fused bead because of the contribution to the analysis from the unknown amount of sulfide. In addition, sulfide cannot be determined directly (or accurately, indirectly) because of the contribution of the unknown amount of sulfate to the analysis and because of the possibility that some sulfide can be lost by volatilization during fusion. Consequently, the method of ISO 29581-1, included as Annex D to this part of ISO 29581, is the reference method for determining the sulfate content of samples containing sulfide species.
Other methods can be used, provided they are calibrated, either against the reference method or against internationally accepted reference materials, in order to demonstrate their equivalence. In the case of dispute, unless otherwise agreed by all parties, only the reference method in ISO 29581-1 can be used. This part of ISO 29581 describes methods that apply principally to cements, but which can also be applied to their constituent materials and to other materials, the standards for which call up these methods. International Standard specifications state which methods can be used.
