SPECTROPHOTOMETRIC ESTIMATION OF TIN

ESTIMATION OF TIN

INTRODUCTION:

In a certain number of methods, Sn (II) is used to reduce substances, which act as redox indicators. Such methods do not permit the estimation of very slight traces, are not very accurate, and necessitate preliminary separations.

With diol (Toluene- 3,4 – dithiol).

Sn (II) gives a red precipitate, which may be estimated, calorimetrically in the colloidal state. Even small traces may be detected by this method.

Limit of detection:

Under normal conditions 1 to 6 mg or 0.1ppm of of tin can be estimated.

The coloration can be extracted with ethers and alcohols.

Interfering ions. Many ions interfere with the results. Thus Bi (III) gives a brick red precipitate, Cu (II), Ni (II), and Co (II) give black precipitates, Ag (I), Hg (II), Pb (II), Cd (II) and As (III), etc. give yellow precipitates. The NO2^- ion interferes. It is however possible to operate in the presence of 20times more Fe and Pb than Sn. Mn (II) and Zn (II) give rise to low results.

The acidity should be accurately fixed.

Sn (IV) is reduced slowly by the reagent and then undergoes reaction. The reagent is usually stabilized by the addition of thio glycolic acid, which rapidly reduces Sn (IV) to Sn (II).

Reagents:

10ml of glycolic acids are added to 0.25ml of melted dithiol. The solution is diluted to 200ml with alcohol and stored in small-stoppered bottles protected from light.

Gum Arabic in 10% solution.

Procedure:

5ml of the solution, containing less than 50mg of Sn (IV), are neutralized with ammonia and then 0.5ml of concentrated hydrochloric acid are added, followed by 0.5ml of reagent.. The mixture is placed on a boiling water bath for 1 minute and, after cooling, shaken with 2ml of gum Arabic. Colour is developed and measured at 530nm. The color is stable for 1 month in a sealed tube in the dark.