A highly selective and sensitive derivative
spectrophotometric method has been developed
for the determination of Fe(II) and Ni(II) in different
mineral vitamins. The method is based on the
formation of binary complexes of Fe(II) and Ni(II)
with 2,4-diamino-5-(2-hydroxy-5-nitrophenylazo)
benzenesulfonic acid sodium salt (Mordant
Brown 33) at pH 5.6 with Tween 20. At lmax 512
and 493 nm, the molar absorbtivity was 2.09 ´ 104
and 0.58 ´ 104 L/mol cm for Fe(II) and Ni(II),
respectively. Fe(II) can be determined in the range
0.55–2.79 mg/mL in the presence of 2.92 mg/mL Ni,
and Ni(II) can be determined in the range
1.17–3.5 mg/mL in the presence of 2.79 mg/mL Fe(II)
in the presence of Tween 20 (4%). The detection
limits were 9.0 and 15.0 ng/mL for Fe(II) and Ni(II),
respectively. The effect of foreign ions was
elucidated. The RSD values were, in all instances,
less than 1.3%. The proposed method was
successfully applied for the simultaneous
determination of Fe(II) and Ni(II) in different mineral
vitamins.