Air oxidation of KI (slow reaction: (4I^- + O_2 + 4H^+ \rightarrow 2I_2 + 2H_2O)) is the main source of blank I₂.
$$I_total = I_blank + I_sample$$
Crude or refined vegetable oils, animal fats, and even many processed lipids contain endogenous antioxidants (e.g., tocopherols, tocotrienols, phospholipids, or added synthetic antioxidants like BHA, BHT, or TBHQ). These compounds act as and oxygen absorbers . Air oxidation of KI (slow reaction: (4I^- +
Lipid samples often contain (e.g., tocopherols, BHT). These reducing agents can react with I₂ before it is titrated: [ I_2 + AH_2 \rightarrow 2I^- + A ] or added synthetic antioxidants like BHA