USGS-NWQL: I-7447: Magnesium, suspended 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. This procedure may be automated by the addition of a sampler, a proportioning pump, and either a strip-chart recorder or a printer or both. |
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Scope and Application
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Suspended recoverable magnesium is calculated by subtracting dissolved magnesium from total recoverable magnesium. Prepared sample solutions containing more than 50 mg/L need either to be diluted. Total recoverable magnesium in water-suspended sediment needs to undergo preliminary digestion-solubilization by method I-3485. |
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Applicable Concentration Range
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0.01 mg/L to 50 mg/L |
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Interferences
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The interference caused by aluminum 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 with use of nitric acid solution. Nitrate, sulfate, and silica interfere, but in the presence of lanthanum chloride-hydrochloric 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 at the time of collection to preserve the samples causes no problem in the following procedure. 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 Descriptions: 250 mL Polyethylene bottles, acid-rinsed. Treatment and Preservation: Use unfiltered sample to rinse bottle, then acidify collected sample with HNO3 to pH <2. For second sample, filter through 0.45-um filter, use filtered sample to rinse containers and acidify 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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I-3485 |
