AOAC Test Method 973.52B

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Source:
AOAC

Method Name:
Hardness of Water. Official Name: Hardness of Water by EDTA Titrimetric Method

Description:
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:
Applicable to drinking water, surface water, and domestic and industrial wastewaters.

Citation:
Official Methods of Analysis of AOAC International, 16th Edition, 4th Revision, 1998 Volume I

Interferences:
Not specified in method.

QC Requirements:
Not Included

Media:
WATER

Subcategory:
Inorganic

Concentration:
None given.

Precision:
Precision and accuracy data were determined using interlaboratory data generated during EPA-managed Water Pollution (WP) performance evaluation studies.

Detection:
-

Revision Number:
15th Edition (1990)



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