SOP for STANDARD WORKING PROCEDURE FOR ESTIMATION OF ARSENIC

PRINCIPLE:

Arsenic is converted into its volatile hydride by Sodium Borohydrate reagent in acid solution. The Hydride is purged continuously by nitrogen into an appropriate atomizer of an Atomic Absorption Spectrometer.

Limit of Detection: 0.02 mg/L

 REAGENTS:

1. Sodium Borohydride : 0.6 % in 0.5 % NaOH

2. Hydrochloride Acid : 5 to 10 M HCl

3. Sulphuric Acid : 2.5 N

4. Potassium Persulphate: 5 % solution. Dissolve 25 gm of Potassium persulphate in water and dilute to 500 ml. Store in glass and refrigerate. Prepare Weekly.

5. Arsenic Stock Solution : Merck 1000 ml mg/L NIST Certified Reference Material or Dissolved 1.32 gm Arsenic Trioxide in water containing 4 gm of Sodium Hydroxide. Dilute to 1000 ml with water ( 1ml = 1 mg of As)

6. Working Solutions: Prepare daily. Prepare series of standard covering the required range (0.02, 0.04, 0.06, 0.08 and 0.1 mg/L). Add 1.5 ml nitric acid per liter to all working standard solution before diluting to volume.

PROCEDURE:

Preparation of Sample: Transfer 100 ml sample to 200 ml beaker. Add 1 ml of 2.5 N Sulphuric Acid and 5 ml of 5 % Potassium Persulphate. Boil gently on a preheated hot plate for about 30 minutes or until the final volume reduced to 10 ml. Do not let sample go to dryness. After manual digestion, dilute to 100 ml with water.

Analysis: Operate the instrument as per SOP. Aspirate the blank. Then aspirate series of standards and then aspirate the sample solution. Read the concentration in µg/L of Arsenic directly. 

REFERENCE: IS 3025 (Part 37) - 1998