Quantification of technetium-99 in wastewater by means of automated on-line extraction chromatography – anion-exchange chromatography – inductively coupled plasma-mass spectrometry

Abstract

With more than 30 million medical applications annually, ^99mTc is the most widely used radioisotope. Nevertheless, the discharge of ^99mTc and its radioactive nuclear isomer ⁹⁹Tc through medical facilities into the aqueous environments is mostly unknown. This is related to the low absolute Tc mass used in medical examinations and consequent trace levels of Tc emitted from respective facilities. In this work, a new approach employing automated on-line extraction chromatography and anion-exchange chromatography was developed and coupled to inductively coupled plasma-mass spectrometry. The extraction column was filled with TK201 resin to preconcentrate, purify and elute pertechnetate ([⁹⁹Tc]TcO₄⁻) as the most relevant Tc species. The eluting ⁹⁹Tc fraction was focused and separated on an anion-exchange chromatography column and directly calibrated into a mass flow using an on-line isotope dilution-like approach named isobaric dilution analysis. To accommodate ultra-trace levels in strong matrices with high grades of particulate contamination, the automated method was complemented by a newly developed manual filtration and preconcentration workflow with TK201 impregnated filter disks, reaching a combined preconcentration factor as high as 4615. An aerosol desolvation nebulization system was used additionally to boost sensitivity, achieving an ultimate limit of detection (LOD) as low as 0.70 ± 0.02 fg kg⁻¹. As proof of concept, a wastewater sample from a retention basin of a local university hospital was collected. This wastewater contained ⁹⁹Tc emitted in diagnostic procedures and levels were determined to be as low as 89 ± 4 fg kg⁻¹.