Spectrophotometric Estimation of Gold at 565nm

ESTIMATION OF GOLD

Using Rhodamine B

In the form of AuCl₄^-, Au(III) gives rise to a violet complex  with the cation of rhodamine can be extracted with  benzene and iso- propyl ether . The extracted is governed by the concentration of hydrochloric acid and other chlorides.

Interfering ions:

Sb(V), Tl(III), W (VI), Hg(II) (> 250), Fe(III) (>100 µg),  and  Sn (IV) (10µg) also  give the extractable  coloration. When these metals are present , the gold may be separated by precipitation with hydroxylamine hydrochloride , using  tellurium as an entraining agent .

Reagents:

1.      Hydrochloride acid, 6M 250ml of water are added to 250ml of concentrated hydrochloric acid.

2.      Ammonium chloride , saturated: 150g of ammonium chloride are dissolved in 500ml of water .

3.      Rhodamine B, 0.04% : 200mg of rhodamine B are dissolved in 500ml of water.

4.      Iso propyl ether.

Operating procedure:

2.5ml of 6M hydrochloric acid and 5.0ml of ammonium chloride are added to 5ml of solution containing 10 to 20µg of gold: the volume is made up to 15ml.  5ml of rhodamine B are added, followed by 10ml (accurately measured) of iso propyl ether. The mixture is vigorously shaken 100times, allowed to settle and the colorimetric determination is then performed at 565nm.