USGS-NWQL: I-3448: Magnesium, total recoverable, FLAA
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Official Method Name
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Magnesium, atomic absorption spectrometric, direct |
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Current Revision
| 1985 |
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Media
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WATER |
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Instrumentation
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Flame Atomic Absorption |
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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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Magnesium is determined by flame atomic absorption spectrometry (Fishman and Downs, 1966). Lanthanum chloride is added to mask interferences. Effluent samples must undergo a pre-liminary nitric acid digestion followed by a hydrochloric acid solubilization. |
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Scope and Application
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This method may be used to analyze water-suspended sediment. For ambient water, analysis may be made on a measured portion of the acidified water-suspended sediment sample. For all other waters, including domestic and industrial effluent, the atomic absorption procedure must be preceded by a digestion-solubilization as specified below. In cases where the analyst is uncertain about the type of sample, the digestion-solubilization procedure must be used. Two analytical ranges are provided: from 0.1 to 10 mg/L of Mg and from 2.5 to 50 mg/L. Samples containing magnesium at concentrations greater than 50 mg/L need to be diluted. |
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Applicable Concentration Range
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0.10 mg/L to 50 mg/L |
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Interferences
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The interference caused by aluminum at concentrations greater than 2,000 ug/L is masked by addition of lanthanum. Because low magnesium values result if the pH of the sample is above 7, standards are prepared in hydrochloric acid solution and samples are preserved in the field using a nitric acid solution. Nitrate, sulfate, and silica interfere, but in the presence of lanthanum chloride-acid solution at least 2,000 mg/L, 1,000 mg/L, and 200 mg/L, respectively, can be tolerated. The addition of nitric acid to the sample as a preservative at the time of collection causes no problem in the following procedure. Samples should be evaporated just to dryness following HNO3 digestion to avoid any possible nitrate interference. Sodium, potassium, and calcium cause no interference at concentrations less than 400 mg/L. |
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Quality Control Requirements
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Calibrate instrument using calibration standards (CAL). Quality control samples (QCS) and laboratory blanks (LB) analyzed at a minimum of I each after every 10 samples |
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Sample Handling
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Container Description: 250 mL Polyethylene bottle, acid-rinsed. Treatment and Preservation: Use unfiltered sample to rinse bottles, then acidify collected sample with HNO3 to pH < 2. |
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Maximum Holding Time
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180 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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