Spectrophotometric determination of gold by reaction with molybdate and nile blue in the presence of PVA

A spectrophotometric method for the determination of gold has been developed, based on the reaction of gold(III) with molybdate and nile blue (NB) to form an ion-association complex in the presence of poly(vinyl alcohol). The molar absorptivity at 595 nm is 2.71 × 10⁵ l mol^–1 cm^–1. Beer's law is obeyed over the range 0–16 g of gold per 25 ml. The relative standard deviation evaluated from seven independent determinations of 0.4 g/ml of gold is 2.6%. The limit of detection is 0.011 g/ml. The molar ratio of Au to NB in the complex is established to be 1 2. Over 30 foreign ions were tested for interference; Pt(IV), Sb(III), W(VI) and SiO ₃ ^2– interfered and had to be separated from gold on polyurethane foam. The method can be applied to the spectrophotometric determination of trace amounts of gold in powdered carbon and some ores.