Investigation of cell gas modes for accurate selenium isotopes analysis in tea leaves using ICP-QQQ-MS.

Accurate and sensitive determination of selenium (Se) in tea leaves is analytically challenging due to its low natural abundance and matrix-derived spectral interferences. This study evaluated the performance of inductively coupled plasma triple quadrupole mass spectrometry (ICP-QQQ-MS) under different collision and reaction cell gas conditions for isotope-specific Se determination in tea leaves. Four Se isotopes, including 77Se, 78Se, 80Se, and 82Se, were assessed using He, high-energy He (HEHe), H2, O2, and O2 + H2 modes. He mode showed poor accuracy, with a substantial over-recovery of 125.82-318.37%, suggesting unresolved polyatomic interferences. Increasing the helium flow in HEHe mode improved recoveries to 91.28-127.59%, but isotope-dependent variability remained. In contrast, H2 mode achieved acceptable recoveries of 92.43-104.48%, demonstrating effective interference removal during on-mass measurement. The O2-based mass-shift approaches, including O2 and O2+H2 modes, further improved selectivity by converting Se+ to SeO+ product ions, enabling measurement at shifted masses and reducing direct mass overlap from REE-related interferences. The optimized method achieved limits of detection at 0.011-0.71 μg/L and limits of quantification at 0.039-2.35 μg/L. Method accuracy was validated using green tea certified reference material, with measured Se content consistent with the certified value of 0.090 ± 0.030 μg g-1. Application to tea leaf samples enabled reliable Se quantification in a complex plant matrix. Overall, ICP-QQQ-MS cell gas optimisation and isotope selection are essential for accurate Se quantification, impacting sensitivity in tea leaves. The developed approach provides a robust analytical basis for Se analysis in tea and potentially other plant matrices.