AOAC: 973.52B:  Hardness of Water

  • Summary
  • Analytes
  • Revision
  • Data and Sites
Official Method Name
Hardness of Water by EDTA Titrimetric Method
Current Revision
15th Edition (1990)
Media
WATER
Instrumentation
Titration
Method Subcategory
Inorganic
Method Source
  AOAC
Citation
  Official Methods of Analysis of AOAC International, 16th Edition, 4th Revision, 1998 Volume I
Brief Method Summary
Ca and Mg at pH 10 in presence of dye eriochrome black T are wine red. When completely complexed with EDTA, solution becomes blue. Mg must be present for satisfactory end point and is added as MgEDTA. End point sharpness increases with pH, but high pH may cause precipitation of Ca(OH)2 or Mg(OH)2 and cause color changes of dye. pH of 10.0 +/- 0.1 is satisfactory compromise. Limit of 5 min for titration minimizes precipitation. Heavy metal interference is minimized by complexing with cyanide.
Scope and Application
Applicable to drinking water, surface water, and domestic and industrial wastewaters.
Applicable Concentration Range
None given.
Interferences
Not specified in method.
Quality Control Requirements
Not Included
Sample Handling
No information given.
Maximum Holding Time
Relative Cost
Less than $50
Sample Preparation Methods