Figure 8 shows how iron fluorescence overlaps nickel fluorescence in kovar and other glass-sealing alloys. Metal foil filtration is not available to separate these two lines (peaks) as is done with nickel and copper. In order to measure with older XRF instruments, the lower limit for the region of interest for nickel must be moved up to avoid as much iron as possible.

Newer instrumentation successfully employs numerical filtration to subtract the iron line from the nickel line. It is still necessary to perform normalization or other suitable adjustments to account for variations in iron content from lot to lot in kovar and other glass-sealing alloys.

Abstract
Accuracy and Precision
Principle of Measurement
Gold and Nickel Measurements on Copper
Gold and Nickel Measurements on Phosphor Bronze
Gold and Nickel Measurements on Kovar and Other Glass-Sealing Alloys
Gold and Nickel Measurements on FR-4 Circuit Board Substrates
Tin-Lead Solder on Copper, FR-4 Circuit Board Substrates, and Kovar
Tin-Lead Solder on Phosphor Bronze
Adjustments for Part Geometry
Measurement Assurance
Conclusion