USGS-NWQL: I-4471-97: Metals in Water by Inductively Coupled Plasma/Optical Emission Spectrometry, Whole-Water Recoverable
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Official Method Name
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Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory - Determination of Elements in Whole-Water Digests Using Inductively Coupled Plasma-Optical Emission Spectrometry a |
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Current Revision
| 1999 |
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Media
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WATER |
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Instrumentation
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Inductively Coupled Plasma - Atomic Emission Spectroscopy |
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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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Brief Method Summary
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Whole-water recoverable elements are determined simultaneously on a single sample using inductively coupled-plasma-optical emission spectrometry. Sample solution is pumped into a high dissolved-solids tolerant nebulizer to produce an aerosol. The aerosol is subsequently transported by argon gas through a spray chamber and torch assembly into an inductively coupled plasma source where the sample is desolvated, atomized, and the resultant atoms or ions excited. The intensity of light emission that results when the excited-state atoms or ions relax to their ground state is directly proportional to the concentration of the emitting species in solution. Mean concentrations of elements are reported from the three replicate determinations. |
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Scope and Application
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This method is used to determine aluminum, barium, beryllium, boron, cadmium, calcium, cobalt, copper, iron, lead, lithium, magnesium, manganese, molybdenum, nickel, silicon (reported as silica, SiO2), silver, sodium, strontium, vanadium, and zinc in natural whole-water digested by using the in-bottle procedure described by Hoffman and others (1996). |
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Applicable Concentration Range
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Interferences
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Physical interferences are generally considered to be effects associated with sample transport and nebulization processes. Sample matrices that are significantly different than the calibration standards, such as those having high dissolved-solid concentrations (or high specific conductance), might cause changes in the transport and nebulization process leading to significant inaccuracy in the final result. Physical interference effects can be overcome by using dilution or internal standards, or both. Simple dilution reduces the viscosity of the sample solution and the concentration of the matrix salts. Addition of a surfactant to the samples and calibration standards also tends to stabilize sample transport. The use of an internal standard can reduce the effects associated with changing sample transport properties as well as instrument drift. Yttrium is commonly used as an internal standard for ICP-OES analyses. The accuracy of internal standardization relies on the absence of yttrium in the sample. If yttrium is present, results will be negatively biased. Therefore, it is important to verify the absence of yttrium in the samples being analyzed. Spectral interferences occur when constituents in a sample emit radiation at wavelengths close to the analytical wavelength being measured. Unresolved spectral emission at the analytical wavelength can result in significant positive bias in the results. In some instances, the high concentration of an interferent can suppress the emission from an element and result in a negative bias. Relating the apparent elemental concentration to the concentration of the interfering element is used to minimize this type of interference. Other spectral interferences can result from stray light, molecular broadband emission, and spectral-line broadening that contribute to the background or offset in the element signal. Specific conductance can exhibit physical interfence effects because of high dissolved-solid concentrations. |
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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: 250 mL Polyethylene bottle, acid-rinsed. Treatment and Preservation: Use unfiltered sample to rinse bottles, then acidify collected sample with nitric acid (HNO3) to pH < 2. |
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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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USGS-WRIR 96-225 |
