Quantification of [⁹⁹Tc]TcO₄^- in urine by means of anion-exchange chromatography-aerosol desolvation nebulization-inductively coupled plasma-mass spectrometry

To sensitively determine Tc-99, a new method for internal quantification of its most common and stable species, [Tc-99]TcO4-, was developed. Anion-exchange chromatography (IC) was coupled to inductively coupled plasma-mass spectrometry (ICP-MS) and equipped with an aerosol desolvation system to provide enhanced detection power. Due to a lack of commercial Tc standards, an isotope dilution-like approach using a Ru spike and called isobaric dilution analysis (IBDA) was used for internal quantification of Tc-99. This approach required knowledge of the sensitivities of Ru-99 and Tc-99 in ICP-MS. The latter was determined using an in-house prepared standard manufactured from decayed medical (99)mTc-generator eluates. This standard was cleaned and preconcentrated using extraction chromatography with TEVA resin and quantified via total reflection X-ray fluorescence (TXRF) analysis. IC coupled to ICP-MS enabled to separate, detect and quantify [Tc-99]TcO(4)(-)as most stable Tc species in complex environments, which was demonstrated in a proof of concept. We quantified this species in untreated and undiluted raw urine collected from a patient, who previously underwent scintigraphy with a 99mTc-tracer, and determined a concentration of 19.6 +/- 0.5 ng L-1. The developed method has a high utility to characterize a range of Tc-based radiopharmaceuticals, to determine concentrations, purity, and degradation products in complex samples without the need to assess activity parameters of Tc-99(m).