Standard Operating Procedure for Estimating Mercury
1.0 Purpose: To lay down the procedure for the Estimation of Mercury using Atomic Absorption Spectroscopy.
2.0 Aim: This Standard Operating procedure is applicable to the Estimation of Mercury using Atomic Absorption Spectroscopy (AAS) in a Pharmaceutical Laboratory.
Principle: The method used here, called flameless AAS (Atomic Absorption Spectroscopy), is based on the absorption of radiation at 253.7 nm by mercury vapor. Mercury is converted into its elemental state and released from the solution in a closed system. The cold mercury vapor is then passed through a cell positioned in the light path of a mercury Hollow-Cathode lamp in an AAS.
Limit of Detection: 0.0005 mg/l
3.0 Reagents:
3.1 Stannous Chloride: Dissolve 25 gm of stannous chloride in water containing 50 ml concentrated HCL, and dilute to 250 ml with water.
3.2 Hydrochloric Acid: Concentrated
3.3 Nitric Acid: Concentrated
3.4 Mercury Stock Solution: Use Merck 1000 mg/l NIST Certified Reference Material or dissolve 1.354 mg of Mercuric Chloride in about 700 ml of distilled water. Add 10 ml of concentrated Nitric Acid and make it up to 1000 ml (1 ml = 1 mg of Hg).
3.5 Working Solution: Prepare daily. Create a series of standards covering the range (0.01, 0.02, 0.03, 0.04, and 0.05 mg/l). Add 10 ml of Hydrochloric Acid per 1000 ml to all working standard solutions before dilution.
4.0 Procedure:
4.1 Sample Preparation:
4.1.1 Transfer 2000 ml of the sample to an evaporating dish.
4.1.2 Add 5 ml of Nitric acid.
4.1.3 Evaporate gently (do not boil) on a preheated hot plate until the final volume reduces to 20 ml.
4.1.4 Do not let the sample go to dryness.
4.1.5 After manual digestion, dilute 50 ml with water (40 times the concentration of the sample).
4.2 Analysis:
4.2.1 Operate the instrument following the SOP.
4.2.2 Aspirate the blank.
4.2.3 Aspirate the standard solution.
4.2.4 Aspirate the sample solution.
4.2.5 Read the concentration in µg/l of mercury directly.
(Apply the dilution factor of 0.025 because the sample is 40 times concentrated.)
5.0 Reference: IS: 3025 (PART 48)-1994
Related SOP: SOP on Receipt and Handling of Laboratory Samples
6.0 Abbreviations:
SOP: Standard operating procedure
nm: Nano Meter
mg: Milli Gram
Hg: Mercury
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