Safe and Effective Sample Preparation for the Radioanalytical Chemistry

First Reported Application of Borate Fusion in Radioanalytical Sample Preparation

The application in a radioanalytical context was spearheaded by Professor Ian Croudace (Director of the Geosciences Advisory Unit). In a 1996 research contract, the lab had to analyze Pu and U isotopes from 650 soils samples within three months, where borate fusion was selected predominantly because of its safety, speed, and ability for complete dissolution (Croudace et al. 1998).

Safe and Effective Sample Preparation for the Radioanalytical Chemistry

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The high-profile public study centered on investigating ground contamination from alleged damage of a nuclear weapon at the former USAF airbase at Greenham Common in the UK. Before this work, radioanalytical specialists would typically have utilized at least one sample digestion method to extract Pu, U and other radioactive species from soils.

Safe and Effective Sample Preparation for the Radioanalytical Chemistry

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Applications for Nuclear Sectors

Nuclear Decommissioning

Civil power stations and military installations

  • 438 power stations worldwide
  • 149 about to be or being decommissioned

Nuclear Forensics

Illicit trafficking and events involving nuclear and other radioactive material outside regulatory control

  • Emergency responses

Nuclear Waste and NORM Characterization

Naturally Occurring Radioactive Materials

  • IAEA (International Atomic Energy Agency) & ALMERA (Analytical Laboratories for the Measurement of Environmental Radioactivity) lab network
  • 176 labs in 89 countries

Why Fusion for Radionuclides?

The importance of crucial total sample digestion for precise radionuclide characterization, mostly for naturally-occurring radioactive materials (NORM), decommissioning materials, by-products and industrial wastes cannot be denied. The assessment must be effective, fast and accurate, whether it is for disposal, storage or for forensic investigation.

It has been long acknowledged that incomplete dissolution is the main cause of poor analytical performance, and, if a technique is known to have the ability to completely dissolve the most challenging samples, all other digestion methods should not carried out (Sill and Sill 1995).

Strong digestion depends on the nature of the radionuclide(s) present and the sample matrix, but the tipping point is when one is confronted with a refractory matrix, which is reputed to cause problems with a common digestion technique such as acid leaching.

In actuality, approximately 80% of participating laboratories from a new Performance Evaluation Program (MAPEP, Session 30) by the US Department of Energy failed to offer precise results for uranium isotopes in soil samples because of incomplete dissolution of refractory particles using acid leaching methods (Maxwell et al. 2015). Some results were almost 50% lower than the reference values, even when utilizing strong, hazardous hydrofluoric acid.

Reasons to Avoid Acid Leaching

  • Risk of incomplete digestion, particularly refractory elements
    • Analytical errors  
  • Safety reasons
    • Working with HF to decompose silicates can be extremely damaging, as well as being costly and complicated
    • Risks associated with strong acids
    • Not able to be automated  
  • Time consuming
    • Slow, can take hours to digest
    • Needs many manipulations

Safe and Effective Sample Preparation for the Radioanalytical Chemistry

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The X-600 six-positions heavy-duty fully automated electric fusion fluxer can safely process up to 18 samples per hour. Prepares solutions for ICP/AA, peroxide or pyrosulfate fusions and glass disks for XRF. A cold to cold operation that has an automated pouring function with a duration of fewer than 20 minutes.

Safe and Effective Sample Preparation for the Radioanalytical Chemistry

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Advantages Specific to Nuclear Application

Fusion enhances precision by achieving easier digestion of silicate materials and total destruction of mineral lattice structures more effectively than any other technique (Galindo et al. 2007).

This is of considerable significance since some radionuclides are associated with resistant materials or trapped inside the matrix structures. As a result, higher recoveries are attained by fusion, notably for Strontium (Russell et al. 2017) Uranium, Plutonium and Thorium isotopes (Maxwell et al. 2015), and in the case of Cs even total chemical yield recovery compared to 78% with acid leaching using aqua regia (Russell et al. 2014).

Example of lithium borate glass network.

Figure 1. Example of lithium borate glass network. Image Credit: Spex Sample Prep

Depending on the nature of the samples and radionuclide(s) of interest, fusion parameters can also be easily adapted, which makes it a technique of choice because of its great versatility and flexibility and (Braysher et al. 2019). For example, the type of flux can be altered if contaminated by the analyte of interest or for solubility reasons, and sample-to-flux ratio can be easily optimized.

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Additionally, a non-negligible feature of utilizing fusion is the growth in laboratory workflow that stems from the speed of the technique in comparison to different methods. Automating the process has made it easy to alter the fusion conditions depending on the requirements.

Various fusion methods exist to allow numerous labs to use the technique, which includes borate fusion (which is the most attractive), Na2O2 fusion and NaOH fusion. Utilizing an automated fluxer increases repeatability, enabling cold-to-cold operation in less than 20 minutes and is the safest method for fusion.

Along with fusion instruments, automated flux dispensers are now becoming more prevalent with the need to automate repetitive tasks in the lab.  The FluxPenser is a flux dosing machine that automatically calculates and precisely dispenses the needed quantity of flux to the sample. A lab will gain efficiency, accuracy and excellent reproducibility in flux and sample weighing.

Things to Consider

Although fusion has demonstrated its efficiency in numerous applications, there are a few fundamental considerations if one wishes to take advantage of its superiority: a more complex matrix fusion results in high total dissolved salts (TDS) solutions.

Utilizing ion-exchange resins and extraction chromatography can aid in tackling this issue. The sample-to-flux ratio is low to moderate and can, therefore, curb the analysis of ultratrace elements.

Traces of contaminants in flux can also generate concerns, but it is limited nowadays with the utilization of high purity fluxes. The solubility of the sample in the flux may differ depending on its composition. Also, consider the solubility limit of borate flux in the final acid solution.

The initial investment in start-up materials for fusion can appear costly due to the high value of platinumware. However, it is so robust that platinum retains its value even after thousands of fusions and is fully recyclable.

Conclusion

Fusion is vital in reaching complete digestion of a variety of sample matrices with guaranteed precision and is superior to acid leaching in numerous other ways. For example, it is safer because of the lack of hazardous acids and because of being an automated process, but also by being fast and extremely efficient in digesting complex material.

By being adaptable and tough, fusion can prevent incorrect results, which could be detrimental to a laboratory’s reputation. Within a radioanalytical context, it has demonstrated its effectiveness many times over and offers economic benefits for the nuclear industry.

Progress in this sector is vital, and the requirement for correct sample digestion will become even more pertinent in the near future with the growing rate of decommissioning worldwide.

This information has been sourced, reviewed and adapted from materials provided by SPEX SamplePrep.

For more information on this source, please visit SPEX SamplePrep.

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