The tolerance limit of various ions is defined as the largest amount making a variation of less than ±5% in the determination of iron. As shown in Table 1, most of divalent ions whose complexes with 5-Br-PADAP generally have maximum absorption around 538–586 nm, do not produce remarkable interfere at the wavelength of 740 nm. In addition, the tolerance limits can be further improved by the addition of suitable masking agent.