NEMI Method Summary

Method Summary Information

Method Number: I-1338 Media: WATER
Revision: 1985
Method Source: U.S. Geological Survey (USGS)
Subcategory: INORGANIC Analytes in this method
Official Name: Hardness in water by colorimetric titration
Descriptive Name Hardness in water by colorimetric titration
Source Info: USGS Branch of Information Services
Box 25286, MS 417
Federal Center
Denver, CO 80225-0286
Phone: 303-202-4700
Citation: USGS Methods, Volume A1
90099 Byte file
Brief Method
Summary:
 Disodium dihydrogen ethylenediamine-tetraacetate (Na2EDTA) forms a slightly ionized, colorless, stable complex with alkaline earth ions. The indicator Eriochrome Black T is bright blue in the absence of alkaline earths, but with them forms a deep-red complex that has a higher ionization constant than that of the Na2EDTA complex. Hence, with Eriochrome Black T as an indicator, the alkaline earth can be titrated with Na2EDTA. All alkaline earth titrate approximately stoichiometrically. The titration should proceed immediately upon addition of the indicator, because the color of the solution fades after standing. The optimum pH of the titration is 10.4 or above. Additional information on the principle of the determination is given by Goetz and others (1950), and by Botha and Webb (1952).
Scope And
Application:
 This procedure is applicable to most natural and treated water, but the method fails conspicuously at times with acidic or polluted water that contains excessive amounts of heavy metals.
Applicable
Conc Range:
 None given.
Interferences: (1) Acidic or polluted water that contains excessive amounts of heavy metals. (2) Manganese in higher oxidation states than Mn(II). (3) High aluminum concentrations.
QC Requirements: Not Included
Sample Handling: Container Description: 125 mL polyethylene bottle.
Treatment and Handling: Use unfiltered sample to rinse bottle. Max holding time: 180 days.
Max Holding Time:
 180 days
 
Relative Cost: Less than $50
4781
Page 1