ASTM: D5174: Uranium, Trace, in Water by Pulsed-Laser Phosphorimetry
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Official Method Name
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Standard Test Method for Trace Uranium in Water by Pulsed-Laser Phosphorimetry |
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Current Revision
| Current edition approved Aug. 10, 1998. Originally published as D574-91. |
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Media
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WATER |
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Instrumentation
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Pulsed-Laser Phosphorimetry |
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Method Subcategory
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Radiochemical |
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Method Source
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Citation
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Brief Method Summary
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This test method is based on the utilization of a laser phosphorimeter to determine total uranium, by mass, in water samples. A sample aliquot is pipetted into a pretreated glass vial. Concentrated HNO3 and hydrogen peroxide are added and the sample heated to near dryness. This step is repeated as necessary and the residue is dissolved in dilute HNO3. A complexant is added to an aliquot of this sample and analyzed in the phosphorimeter. For screening purposes only, an aliquot of the sample may be pipetted directly into the phosphorimeter cell and read. This cannot be done if the sample was preserved with HCl or if the matrix is not known. |
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Scope and Application
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This test method covers the determination of total uranium in water in the range of 0.05 ppb or greater. Samples with uranium levels above the laser phosphorimeter dynamic range may be diluted to bring the concentration to a measurable level. This test method was used successfully with reagent water. It is the user's responsibility to ensure the validity of this test method for waters of untested matrices. |
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Applicable Concentration Range
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0.05 and greater ug/L |
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Interferences
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Absorption (Inner Filter Effect) - This effect is more severe with ultraviolet excitation light (337 nm) than with visible excitation because many prevalent compounds have pi-bonding and absorb strongly in this region. Ferric iron and oxy-anions such as nitrate and organic acids are examples. Visible excitation (425 nm) may be absorbed by yellow solutions, for example, chromate. The consequences of this may be reduced signals and low analysis results. Lumiphors - Many organic substances, such as humic acids and organic degradation products from incomplete ashing emit luminescence of varying lifetimes after excitation. An advantage of phosphorescence measurement is the ability to determine if interferences are present by observing the lifetime of the decay. Quenching - Shortened triplet-state lifetime and reduced phosphorescence intensities of the excited uranyl complex result when quenching occurs. Reliable results cannot be obtained when quenching exceeds 80 to 90 %. Reducing agents such as alcohols, halides except fluoride, and metals with electronic energy levels overlapping those of uranyl ion are strong quenching agents. Examples are silver, lead, iron (II), manganese (II), and thallium. Results from single time-gated instruments are particularly sensitive to even mild quenching agents such as aluminum (III), magnesium (II), calcium (II), and strontium (II). Competing Reactions - For this test method to perform well, the uranyl ion must be protected from various intermolecular mechanisms which rapidly quench the uranyl luminescence. Complexation fulfills this need, and examples of effective agents are phosphoric acid, and polyphosphates (Fluran, and Uraplex ). Hydrochloric acid, if present, is an interference unless eliminated during digestion. |
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Quality Control Requirements
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Whenever possible, the project leader, as part of the external quality control program, should submit quality control samples to the analyst along with routine samples in such a way that the analyst does not know which of the samples are the quality control samples. These external quality control samples which usually include duplicate and blank samples, should test sample collection and preparation as well as sample analysis whenever this is possible. In addition, analysts are expected to run internal quality control samples that will indicate to them whether the analytical procedures are in control. Both the external and internal quality control samples should be prepared in such a way as to duplicate the chemical matrix of the routine samples, insofar as this is practical. The quality control samples that are routinely used consist of five basic types: blank samples, replicate samples, reference materials, control samples, and spiked samples. |
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Sample Handling
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Maximum Holding Time
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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