Determination of Radiolysis Products in Zirconium Salt of Di‐(2‐Ethylhexyl) Phosphoric Acid by High Performance Liquid Chromatography/Mass Spectrometry

Abstract

A liquid chromatography with an electrospray ionization‐mass spectrometry (LC‐ESI‐MS) method is described for the quantitative measurement of di‐(2‐ethylhexyl) phosphoric acid (D2EHPA), mono‐(2‐ethylhexyl) phosphoric acid (M2EHPA) in zirconium salt of di‐(2‐ethylhexyl) phosphoric acid (Zr‐D2EHPA). During the solvent extraction process of radioactive waste, the Zr‐D2EHPA extractant may be degraded to D2EHPA, M2EHPA, and PO₄ ⁻³ etc. Amounts of D2EHPA and M2EHPA in Zr‐D2EHPA must be monitored because the production of these compounds means degradation, which leads to a decrease in the extraction yield. Retention behavior for D2EHPA and M2EHPA is studied with a Phenomenex LUNA‐C₁₈ (4.6 mm × 25 cm) analytical column and methanol/H₂O (50 mmol CH₃COONH₄) by LC. Optimum conditions of eluent for the determination of D2EHPA and M2EHPA irradiated with ⁶⁰Co γ‐rays of Zr‐D2EHPA are methanol:H₂O (50 mmol CH₃COONH₄) = 80:20 ratio in the SCAN mode of the MS for D2EHPA and Methanol:H₂O (50 mmol CH₃COONH₄) = 75:25 ratio in the SIM mode of the MS for M2EHPA. Di‐(2‐ethylhexyl) phosphoric acid and M2EHPA compounds are well separated within 10 min. Dynamic ranges are 10–100 µg mL⁻¹ for D2EHPA and 10–200 µg mL⁻¹ for M2EHPA, respectively. The detection limits are 1 µg mL⁻¹ in the SCAN mode of the MS for D2EHPA and 1 µg mL⁻¹ in the SIM mode of the MS for M2EHPA in this system with a 20 µL sample loop.

Keywords:

• Radiolysis products
• γ‐Irradiation
• Zirconium salt
• HPLC/MS