Imaging and mass spectra to locate and identify surface contamination.
Visible staining was observed on internal angled face of a diesel engine injector component. The stain was too thin to be detected by EDX.
The mass resolved image shows the distribution of 56Fe. The inset identifies the region where the stain was observed; as the Fe signal is masked by the surface contaminant.
A mass spectrum taken on the clean base surface shows the composition to be mainly Fe and Cr (with some Na from handling). A similar spectrum from the stain is dominated by the 40Ca signal with the metal signals being significantly reduced.
The stain is positively identified as being Ca based and originating from use of bio-diesel. This known possible fuel contaminant is limited by EU regulations to 5 mg/kg (summed with the Mg content).