Standard Methods: 2340B:  Hardness in Water by EDTA Titration

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Official Method Name
Hardness in Water by EDTA Titration
Current Revision
Standard Methods Online
Media
WATER
Instrumentation
Titration
Method Subcategory
Inorganic
Method Source
  Standard Methods
Citation
  Standard Methods Online - Standard Methods for the Examination of Water and Wastewater
Brief Method Summary
Select sample volume that will allow color change to occur with the 15 mL addition of 0.01M EDTA titrant to the sample. Complete titration within 5 minutes. Dilute 25 mL of the sample to 50 mL. Add 1-2 mL of NH4Cl-NH4OH to get the pH to 10 or 10.1. Add 1-2 drops of Eriochrome Black T or Calmagite. Slowly add 0.01M EDTA titrant and stir, until end solution is blue. For samples with low hardness, use a 100 to 1000 mL sample for titration, and proportionately larger amounts of reagents.
Scope and Application
This method is applicable to all waters. Polluted waters and wastewater samples must be pretreated. See abstract in Method 3030.
Applicable Concentration Range
Method is suitable for all concentration levels.
Interferences
(1) A number of metal ions may cause fading or indistinct end points (Standard Methods 2340C provides a listing of interfering metals and their potential effects). (2) Suspended or colloidal organic matter can interfere with the endpoint.
Quality Control Requirements
not included
Sample Handling
Collect 100 mL in glass or plastic container. Acidify samples to a pH < 2 with HNO3. Analyze within 6 months.
Maximum Holding Time
6 months
Relative Cost
Less than $50
Sample Preparation Methods
SM 3030