USGS-NWQL: I-1020: Acidity, water, titrimetric
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Official Method Name
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Acidity, electrometric titration |
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Current Revision
| Revised 1985 |
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Media
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WATER |
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Instrumentation
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Titration |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Methods for the Determination of Inorganic Substances in Water and Fluvial Sediments, Techniques of Water-Resources Investigations of the United States Geological Survey, Book 5, Chapter A1 Edited by Marvin J. Fishman and Linda C. Friedman |
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Brief Method Summary
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Acidity is determined by titrating the sample with a standard solution of a strong base to an electrometrically observed end point pH of 8.3. The titration is carried out at room temperature, except that the sample is heated briefly near the end of the titration to increase the rate of hydrolysis of metal ions present. For additional information concerning the determination of acidity and for instructions for constructing an electrometric titration curve, see ASTM Method D 1067-82, "Standard Methods of Test for Acidity or Alkalinity of Water," (American Society for Testing and Materials, 1984). |
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Scope and Application
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This method is applicable to many acidic samples. When the sample is suspected or known to contain mostly weak acids, however, the construction of a neutralization curve is imperative, and the acidity value is reported and interpreted in terms of the character of the curve obtained. |
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Applicable Concentration Range
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> 0.1 mg/L |
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Interferences
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Dissolved gases that are acidic, such as CO2 and H2S, may easily be lost from the sample. If any substantial part of the acidity is due to gaseous solutes, special care must be taken to prevent their escape prior to and during the titration. Gases are less soluble in warm water than in cold; hence, the sample must be kept chilled until analyzed, and even then the analysis must be performed as soon as possible. Stirring and agitation of the sample cause expulsion of dissolved gases; care must be taken to avoid unnecessary agitation of the sample. A tightly capped bottle is essential for storing and transporting samples. The determination should be performed at the time of sampling for greatest accuracy. |
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Quality Control Requirements
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None. |
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Sample Handling
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Container Description: 250 mL Polyethylene bottle. Treatment and Preservation: Use unfiltered sample to rinse bottles; container size dependent on laboratory schedule. |
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Maximum Holding Time
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30 days |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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