Area Peak Factors and Standard Assignments

Area Peak Factors and Standard Assignments

Another consideration in assigning standards concerns the use of Area Peak Factors (APFs) for corrections to effects of peak shift and shape changes. These occur for light element K lines as well as L lines of certain elements, e.g. Co (recall that this is due to involvement of electrons from the valence shell, L shell for K lines, M shell for L lines). These changes are most noticeable on TAP and Pb-stearate, barely if at all with the layered synthetic diffractors. When analysis of the affected elements/lines is to be performed (typically oxygen, nitrogen, carbon and boron but possibly silicon, aluminum and sulfur), you need to plan the use of APF corrections for the most accurate results. The actual APF values selected will depend upon the standard assigned, and also the specific crystal used on the spectrometer.

For example, when analyzing for C Kα and using Fe3C as your carbon standard, your APF value for C Kα in a Cr7C3 matrix might be 0.80. However, if instead, you re-assigned your carbon standard to TiC, you must use APF values relative to TiC rather than Fe3C. If they are available in the Empirical APF database (EMPAPF.DAT), just change the APF values for C Kα. Otherwise you would need to calculate the Fe3C APF values relative to TiC. Some typical Fe3C APF values for C Kα, recalculated relative to TiC and Cr7C3, are shown in the table below :