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A Piecewise Local Partial Least Squares (PLS) Method for the Quantitative Analysis of Plutonium Nitrate Solutions.

Authors
  • Lascola, Robert1
  • O'Rourke, Patrick E1
  • Kyser, Edward A2
  • 1 1 1073 Science and Technology Directorate, Savannah River National Laboratory, Aiken, SC, United States. , (United States)
  • 2 2 Environmental Stewardship Directorate, Savannah River National Laboratory, Aiken, SC, United States. , (United States)
Type
Published Article
Journal
Applied Spectroscopy
Publisher
SAGE Publications
Publication Date
Dec 01, 2017
Volume
71
Issue
12
Pages
2579–2594
Identifiers
DOI: 10.1177/0003702817734000
PMID: 28884597
Source
Medline
Keywords
License
Unknown

Abstract

We have developed a piecewise local (PL) partial least squares (PLS) analysis method for total plutonium measurements by absorption spectroscopy in nitric acid-based nuclear material processing streams. Instead of using a single PLS model that covers all expected solution conditions, the method selects one of several local models based on an assessment of solution absorbance, acidity, and Pu oxidation state distribution. The local models match the global model for accuracy against the calibration set, but were observed in several instances to be more robust to variations associated with measurements in the process. The improvements are attributed to the relative parsimony of the local models. Not all of the sources of spectral variation are uniformly present at each part of the calibration range. Thus, the global model is locally overfitting and susceptible to increased variance when presented with new samples. A second set of models quantifies the relative concentrations of Pu(III), (IV), and (VI). Standards containing a mixture of these species were not at equilibrium due to a disproportionation reaction. Therefore, a separate principal component analysis is used to estimate of the concentrations of the individual oxidation states in these standards in the absence of independent confirmatory analysis. The PL analysis approach is generalizable to other systems where the analysis of chemically complicated systems can be aided by rational division of the overall range of solution conditions into simpler sub-regions.

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