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Spectrophotometry with Internal Standardization

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Method for Precise Determination of Metals in their Solutions by Means of Spectrophotometry with Internal Standardization

Tech Area / Field

  • FIR-INS/Nuclear Instrumentation/Fission Reactors
  • CHE-ANL/Analytical Chemistry/Chemistry

Status
3 Approved without Funding

Registration date
06.06.2001

Leading Institute
Khlopin Radium Institute, Russia, St Petersburg

Collaborators

  • European Commission / Joint Research Center / Institute for Reference Materials and Measurements, Belgium, Geel\nUS Department of Energy / New Brunswick Laboratory, USA, IL, Argonne\nInternational Atomic Energy Agency, Austria, Vienna

Project summary

Contents of noble metals (ruthenium, rhodium, and palladium) in the fission products, that are accumulated in the wastes of spent nuclear fuel treatment – is comparable with natural resources of these elements. This provides an actuality of precise methods development for determination of platinoids. Proposed variants of fission platinoids recovery from spent nuclear materials (ISTC Project 1052) necessarily require development of analytical methods allowing to determine these elements high-accurately both in mixed and inpidual solutions. Spectrophotometry also can be used for precise determination of some REE, in particular, erbium that is added to nuclear fuel as neutron burnable absorber, and lutetium, which is used as a spike for control of reservoir filling with liquid radioactive wastes.

A highest accuracy (better than 0.2%) is needed when standard reference materials are certified for contents of inpidual elements. Such certified reference materials (CRM) assure traceability of analyses results, when they are drawn by various methods and in different laboratories.

The most precise of analytical methods are electrochemical ones. However, they require very complex and continuous analysis procedures. At the same time, features of spectrophotometric methods are relatively simple analysis procedure, and high capacity. A common currency of spectrophotometric methods and devices, their relative simplicity, universality and high capacity, as well as the research purposed for spectrophotometry precision increase which are having been performed for 20 years at the Khlopin Radium institute, give a good background for further improvement of such methods.

In the frame of the present project, a new approach to precision assurance of spectrophotometry methods will be realized – a principle of internal standardization. According to this principle, light absorption is measured simultaneously in two spectral intervals, when the analyzed solution is exposed to 'white' light. First of these intervals is an analytical band of the element to be determined (its absorbance maximum), and the other one corresponds to transparent spectral window, where light absorption is close to zero. In such a case, a ratio of light intensity values in analytical band and transparent window is used as an analytical signal. Forasmuch both intensities fluctuations – related to light source instability, drift of amplifying factor, bad reproducibility of cuvette position geometry, etc. – are correlated, a relative random error of the ratio is significantly less than the error of measurement of the absolute signal of determined element; this can be confirmed by the formula: DR2 = 2D2(1– r), where D and DR – relative standard deviations of direct intensity measurement results and of their ratio, correspondingly, r is a factor of two absolute signals correlation. The principle works when r > 0.5.

In practice, these conditions are realized in the prototype of two-channel spectrophotometric analyzer, recently constructed at the Radium institute. In this device, light intensity measurement in both spectral intervals is performed by the very same detector and amplifier. The analytical band is separated with the monochromator, and the reference transparent wavelength – with interference filter; device background is measured when light is intercepted. The analyzer was used for precise determination of neodymium, rhodium, and some actinides in their solutions. Obtained RSD for different materials varies from 0.07% to 0.16%, therefore, total error is decreased approximately in two times (in relation to existing spectrophotometric methods).

A goal of the project is development of precise spectrophotometric methods for determination of natural uranium, some REE and platinoids in their solutions, basing of the principle of internal standardization. As a result of the project, a two-channel spectrophotometric analyzer will be designed, standard analysis operation procedures for specific elements will be developed and certified.

Successful project execution will make a contribution to tackling of international problems of standardization and traceability of measurements, provision of safeguards of nuclear weapons non-proliferation, and waste recovery of spent nuclear fuel reprocessing, that corresponds to ISTC goals.


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