Silver Auto Titrator Model : ST-9 Figure 1.

Silver is one of the one of the most famous ornamental metal and due to its intrinsic beauty it is made into rings, bracelets, ear-rings and other jewellery items, ornamental utensils, cutlery, tray dishes and coins.

Silver's weakest point is its notorious tarnishing habit. Fresh silver has a bright metallic white color but almost invariably turns yellowish to blackish upon expose to air which is due to its chemical reaction with Sulphur present in Hydrogen Sulphide found in small quantities in the atmosphere. It is not affected by Oxygen or Water.

What XRF technique reveals….??????
XRF mapping of Silver Alloys shows in addition to Silver the presence of a host of metals. Copper, Zinc, Nickel, Cadmium, Lead, Iron. This makes the Silver Alloy non-homogeneous.

A purity check at different points of Silver Alloy using XRF method gives different percentage(%) values of Silver content .In view of this XRF check in not recommended to test the purity of Silver Alloys.

A reliable method for assaying of Silver by Potentiometric (Volumetric) Titration is described in this note.

PRINCIPLE :
Potentiometric Titration involves measuring the changes in the electromotive force (emf) brought about by the addition of titrant (KCl/NaCl) of precisely known concentration to the test solution (silver dissolved in dilute Nitric Acid). The equipment named Silver Auto Titrator Model ST-9 needed to carry out the potentiometric titration is illustrated in Figure 1.

Steps Involved in Purity determinaton of Silver by PotentiometricTitration
Step 1 : Prepare potassium chloride solution.
Step 2 : The Silver Sample is weighed accurately .
Step 3 : The Silver sample is transferred to a titration beaker.
Step 4 : The Silver Sample is dissolved in dilute Nitric Acid.
Step 5 : The Resulting Silver Nitrate Solution is then analysed by Silver Auto Titratior by adding Potassium Chloride solution automatically, via a burette. A Silver Electrode detects the change in electrical conductivity of the solution, until it finds the end point of the titration, when all Silver has been precipitated as Silver Chloride. The amount of Potassium Chloride needed to reach this point shows how much Silver was present in the original sample.
Step 6 : The fineness is automatically calculated and the Silver content of the sample in parts per thousand is printed out.

The analysis curve and the result obtained of a Sterling Silver Chain is shown in figure 2

Conclusion : The Potentiometric (Volumetric) titration for assaying of Silver using Silver Auto Titrator Model : ST-9 is very precise, accurate and economical, complying with BIS Guidelines/NABL protocols.