Quantification of Technetium-99 in Wastewater Using Online Preconcentration and Anion-Exchange Chromatography Coupled with Inductively Coupled Plasma-Mass Spectrometry

Technetium-99 (⁹⁹Tc) is a significant anthropogenic radionuclide released into the environment, primarily from nuclear weapons development and nuclear power production. Additionally, its nuclear isomer, technetium-99m (^99mTc), is extensively used in diagnostic imaging for scintigraphy, with approximately 30 million administrations globally each year. Despite the relatively small amount released, the pervasive use of ^99mTc-based tracers—accounting for about 85% of all scintigraphic examinations—necessitates monitoring its discharge into freshwater systems.

⁹⁹Tc, with a half-life of approximately 211,100 years, is a weak beta emitter, requiring extensive manual preconcentration from large sample volumes and long recording times for beta-counting. However, advances in ICP-MS over the past decades have introduced new strategies for detecting ⁹⁹Tc, offering improved sensitivity, higher matrix tolerance, and faster results with fewer requirements to account for interfering radioisotopes. A significant challenge remains the limited availability of accessible elemental standards for 99Tc quantification.

The New Study:

A group of international researchers has now combined various methods for preconcentration and species separation to enhance the detection power of ICP-MS. They employed a calibration strategy based on isobaric dilution analysis (IBDA). Using a commercial sample preparation station, the entire process of preconcentration, species separation, and online IBDA quantification was automated. This method reduces the need for extensive manual sample preparation, enabling feasible and repeatable monitoring of trace amounts of ⁹⁹Tc in complex environments.

Figure: Schematic depiction of the combined off-line preconcentration/on-line ExC-IC-ICP-MS method

To investigate the approach's feasibility, a wastewater sample was collected from a retention basin at a local university hospital. Given the complex matrix with dissolved and undissolved contaminants, the online method was complemented by additional offline filtration, clean-up, and preconcentration procedures.

The online preconcentration and separation process was conducted using a modified commercial sample preparation station (ESI prepFAST IC). The system featured a sample loop of 11.035 mL, an ExC column with approximately 100 mg of TK201 resin, and an IC column on the third valve.

To achieve the necessary detection power, a total sample volume of 110.35 mL was loaded onto the ExC column by repeating the loading step ten times. The method's sensitivity can be adjusted by changing the number of loading steps.

After sample loading, the ExC column was washed with 0.1 M HNO3 to reduce potential interferences. Elution was performed via the IC column (IonPac AG-9-SC, 4 x 50 mm) using a two-step gradient with NH₄OH solution to focus the peaks and separate ⁹⁹Tc from interfering substances. For further detection power enhancement, the eluent was injected into the ICP-MS via an aerosol desolvation nebulization system, achieving an ultimate limit of detection (LOD) as low as 0.70 ± 0.02 fg·kg-1. Accurate quantification in the presence of a complex matrix was achieved by directly calibrating the eluent into a mass flow using online isobaric dilution analysis.

The entire automated process took approximately 75 minutes, resulting in a preconcentration factor of 4615 when combined with offline sample treatment. Using this combined approach, the researchers determined the ⁹⁹Tc concentration in a sample from the retention basin at the local university hospital to be 89 ± 4 fg/kg.

Conclusion: 

The authors concluded that the developed method offers a robust opportunity for environmental monitoring of technetium-99, enhancing our understanding of its discharge from various sources. This technique holds promise for improving the monitoring and management of ⁹⁹Tc contamination in freshwater systems.

M. Horstmann, C.D. Quarles Jr., S. Happel, M. Sperling, A. Faust, D. Clases and U. Karst, Quantification of technetium-99 in wastewater by means of automated on-line extraction chromatography – anion-exchange chromatography – inductively coupled plasma-mass spectrometry. J. Anal. At. Spectrom., 2024, DOI: 10.1039/D4JA00270A.

Used Instrumentation:

Elemental Scientific - prepFAST IC