SOP for STANDARD WORKING PROCEDURE FOR ESTIMATION OF SILVER

PRINCIPLE:

Metal in solution are determine by Atomic Absorption Spectrophotometry. Suspended metals 

are separated by membrane filtration or suspension is dissolved and analyzed

Limit of detection: 0.01 mg/l

REAGENTS:

1. Deionized Distilled water: Distilled, ammonia free. Pass through exchange column of mixed strongly acidic cation and strongly basic anion exchange resins. Regeneration resins according to manufacturers instruction.

2. Nitric Acid: (1:499)

3. Hydrochloric Acid: (1:1)

4. Silver Stock Solution: Merck 1000 mg/l NIST Certified Reference Material or accurately weight 1.575 gm of silver Nitrate into a beaker and add water + 10 ml redistilled Nitric Acid. When metal is completely dissolved, transfer quantitatively into 1000 ml volumetric flask and dilute to volume with water.

5. Lanthanum stock solution: Slowly add 250 ml HCl to 58.65 g lanthanum oxide (La2O3, purity 99.9 % by mass) dissolve and dilute to 1000 ml.

6. Working Solutions: Prepare daily. Prepare a reagent blank and a sereies of 100 ml standards containing 0.1 0.2, 0.3, 0.4 and 0.5 mg/L of silver by diluting a suitable volume of the standard solution. Add 1.5 ml nitric acid per liter to all working standard solution before diluting to volume. Add 1 ml lanthanum chloride for every 10 ml making the working standard solution.

  

PROCEDURE:

Preparation of Sample:

Transfer 1000 ml well-mixed sample to the evaporation dish and add 3 ml nitric acid. Heat and evaporate to 20 ml (do not boil). Cool and add 3 ml nitric acid and heat until digestion is complete, Add 2 ml HCl (1:1 v/v) and heat gently to dissolve the residue. Wash the evaporation dish for 3 to 4 times with water and filter. Wash the filter and discard. Dilute the filtrate & make up 100 ml volume with water. (10 times concentrate the sample)

Analysis: Operate the instrument as per SOP. Aspirate nictric acid (1:499) as blank. Then aspirate series of standards and then aspirate the sample solution. Read the concentration in mg/L of Silver directly.

(Apply the dilution factor 0.1 because the sample is concentrate 10 times)

REFERENCE: IS 13428: 1998 (Annex J)