Undetected light elements in alloys example. Consider two iron alloys, a cast iron and a steel grade, both having 0.5-0.8% manganese in the specifications. Both of these grades would be expected to analyze as ~99.2-99.5% Fe and ~0.5-0.8% Mn because the other elements would be invisible (in the case of P and S in this matrix and at this concentration level). However, the %iron content actually differs by ~6%
UNS_F10004, Grey Cast Iron HB
C: 3.4-3.7%
P: 0.0-0.25%
S: 0.0-0.15%
Si: 2.3-2.8%
Mn: 0.5-0.8%
Fe: 92.3-93.8%
UNS_G11080, Resulfurized Carbon Steel
C: 0.08-0.13%
P: 0.0-0.004%
S: 0.08-0.13%
Si: –
Mn: 0.5-0.8%
Fe: 98.9-99.3%