Spectrophotometric determination of cobalt in tin–cobalt alloy plating solution with picramazochrom

Cobalt reacts with picramazochrom to form a green complex with a apparent molar absorption coefficient of 2.62 × 104 L/(mol·cm) at the wavelength of 650 nm in a solution consisting of ammonium citrate and ammonia at pH 10. Beer’s law is obeyed in the range of 0-50 μg cobalt in a 25 mL bath. Sample analysis showed that the relative standard deviation was less than 2%.