Spectrophotometric Estimation of Antimony

ESTIMATION OF ANTIMONY

Using Rhodamine B

In fairly concentrated hydrochloric acid in the presence of Rhodamine B, Sb (V) gives a violet-red compound RH SbCl₆ which can be extracted, in particular, by isopropyl ether and benzene.

 Sensitivity:

Co-efficient of molar extinction co-efficient e»40,000at at 545nm in isopropyl ether.

Interfering ions:

Oxidizing agents such as the nitrate, ion, can destroy the dye.

Au (III), Ti (III), Fe(III), Ga(III) give analogous reactions . W (IV) is precipitated.

Alternatively, Sb (V) first separated with isopropyl ether from 1-2 N HCL. Colorimetrically is then carried out directly in the solvent after the addition of reagent., excess of which remains in aqueous solution. The operating procedure for this method will be described below.

Fe (III), which interferes, may be reduced by hydroxylamine.

In this way it is possible to estimate 2 mg of antimony in the presence of 30mg of iron. Ti (III), As (III), and Au (III) interfere when present in the amounts exceeding 250mg.

Oxidation of Sb (III) to Sb (V)

In general, Sb is initially present in its trivalent form, which may be oxidized by ceric salts.

Oxidation can only take place in sufficiently concentrated hydrochloric acid 6M HCL. The solutions often contain Sb (IV) and since this is only oxidized very slowly under these conditions. The excess of oxidizing agent is subsequently removed by reaction with additions of hydroxylamine.

The compositions of Sb (V) solutions change very rapidly on standing, doubtless to condensation.

Reagents

Sodium Sulphite 1%

Hydrochloric acid:

Ceric Sulphate: 3.3g of anhydrous ceric sulphate are dissolved in 100ml of 0.5M(3/100) sulphuric acid

Hydroxylamine hydrochloride, 1 %;

Washing solution: I g of hydroxylamine hydrochloride in 100ml of M hydrochloric acid;

Rhodamine B:

200mg in 100ml of M hydrochloric acid

Isopropyl ether saturated with acid by shaking with M Hcl

Standard Solution of antimony: A quantity of Sb₂ O₃ of guaranteed purity is weighed out and dissolved in 100ml of 6N (1/2) hydrochloric acid. The solution is made up to 100ml of 6 N (1/2) HCL. The solution is made up to 1000ml. Under these conditions, 10197g of Sb₂O₃ corresponds to 1000mg of antimony per ml. This is diluted with N HCL to obtain 2 mg /ml

Operating procedure:

Oxidation of Sb (III).

10ml of concentrated hydrochloric acid and 2ml of sulphite are added t 10ml of a solution containing 5-50mg of antimony, and the mixture is shaken with 3ml of ceric salt. 10 drops of hydroxylamine solution are then added; the solution is further agitated, and followed to stand for one minute.

Separation of Sb (v)

The solution as prepared above is transferred to a separating funnel with 60ml of water and 5ml of isopropyl ether, and is shaken for 30 seconds. The aqueous phase is separated, 2ml of the washing solution are added to the organic phase, and the funnel shaken for 1-2 seconds the aqueous phase is then drawn off . 2ml of  hydrochloric acid are added to the solvent the funnel is shaken for a further few seconds and the aqueous phase separated

Colorimetry/Spectrophotometry.

2ml of Rhodamine are added to the solvent and shaken for 10 sec. The solvent phase is then transferred into a 25 ml measuring flask, made up to volume with the solvent, and estimated colorimetrically at 550 nm