USGS-NWQL: I-1586-85: pH of Water Samples by Ion Selective Electrode
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Official Method Name
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pH, Electrometric, Glass-Electrode |
|---|---|
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Current Revision
| 1989 |
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Media
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WATER |
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Instrumentation
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Ion Selective Electrode |
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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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Samples are analyzed on a standardized pH-selective electrode. This procedure may be automated with commercially available instrumentation. |
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Scope and Application
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This method may be used to determine the pH of any natural or treated water, and any industrial or other wastewater. The pH electrode is standardized with buffer solutions of pH 4.00, 7.00 and 9.00. If samples with pH less than 4 or greater than 9 are analyzed, standardization with additional buffers will be necessary. |
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Applicable Concentration Range
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4.0 - 9.0 (for normal samples) |
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Interferences
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The determination is not affected by the presence of color or turbidity, or of organic or colloidal material. Oxidizing and reducing substances do not impair the accuracy of method. The pH measurement is temperature dependent, and a significant error results if the temperatures of the buffers and samples differ appreciably. However, a variation of less than 5oC has no significant effect except in the most exacting work. For samples having abnormally high sodium levels, corrections may be necessary. This correction varies with the type of electrodes used; hence, see the manufacturer's instructions for the necessary computations. |
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Quality Control Requirements
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Quality-control samples area analyzed at a minimum of one in every ten samples. These QC samples include at least one of each of the following: blanks, quality control samples, third party check solutions, replicates, and spikes. Correlation coefficients for calibration curves must be at least 0.99. QC samples must fall within 1.5 standard deviations of the mean value. If all of the data-acceptance criteria in the SOPs are met, then the analytical data are acceptable. |
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Sample Handling
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Description, Treatment and Preservation: 250 or 500 mL Polyethylene bottle. Use unfiltered sample to rinse bottles. |
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Maximum Holding Time
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180 days from sampling |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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