The Limit of detection/ limit of quantitation of sodium lauryl sulphate to be determined by preparing various concentrated solutions of sodium lauryl sulphate and comparing intensity of blue colour in methylene chloride layer of standard solution.
Procedure:
Preparation of methylene blue (1 g/l solution): Dissolved 10 mg of methylene blue in 10 ml of purified water.
Preparation of mixture of methylene blue (1 g/l solution) and dilute sulphuric acid (solution A):
Transferred 1 ml of 1g/l solution of methylene blue and 20 ml of dilute sulphuric acid to 25 ml volumetric flask and mixed.
Blank Preparation:
Transferred 2 ml of solution A to one glass test tube (30 ml). Added 2 ml of methylene chloride and shaken for 2 minutes. Allowed to stand for 1 minute and recorded the results in table 2.
Preparation of stock solution (100 mcg/ml):
Transferred about 0.1 g of sodium lauryl sulphate, accurately weighed to 10 ml volumetric flask, added 5 ml of water and shaken till the material completely dissolve, made to volume with water. Transferred 1 ml of resulting solution to 10 ml volumetric flask, made to volume with water and shaken. Further transferred 1 ml of resulting solution to 10 ml volumetric flask, made to volume with water and shaken.
Preparation of 5 mcg solution: Transferred 0.05 ml of stock solution to glass test tube, added 2 ml of solution A and shaken for 2 minutes. Added 2 ml of methylene chloride and shaken for 2 minutes. Allowed to stand for 1 minute and recorded the results in table 3.
Preparation of 8 mcg solution: Transferred 0.08 ml of stock solution to glass test tube, added 2 ml of solution A and shaken for 2 minutes. Added 2 ml of methylene chloride and shaken for 2 minutes. Allowed to stand for 1 minute and recorded the results in table 3.
Preparation of 10 mcg solution: Transferred 0.1 ml of stock solution to glass test tube, added 2 ml of solution A and shaken for 2 minutes. Added 2 ml of methylene chloride and shaken for 2 minutes. Allowed to stand for 1 minute and recorded the results in table 3.
Preparation of 15 mcg solution: Transferred 0.15 ml of stock solution to glass test tube, added 2 ml of solution A and shaken for 2 minutes. Added 2 ml of methylene chloride and shaken for 2 minutes. Allowed to stand for 1 minute and recorded the results in table 3.
Acceptance criteria: Blue colour should be clearly visible in the methylene chloride layer.