Final answer:
In flame atomic absorption, the absorbance signal for iron may decrease in the presence of high concentrations of the polyatomic sulfate ion because iron forms a stable complex with sulfate, reducing its absorption.
Step-by-step explanation:
In flame atomic absorption with a hydrogen-oxygen flame, the absorbance signal for iron may decrease in the presence of high concentrations of the polyatomic sulfate ion because iron forms a stable complex with sulfate, reducing its absorption.