Precise Quantification of 36Cl Isotope Using Negative Thermal Ionization Mass Spectrometry with Total Evaporation and Isotope Dilution

Abstract

We developed a sensitive analytical method for precise quantification of radioactive 36Cl in nuclear power plant wastewater using total evaporation and isotope dilution combined with negative thermal ionization mass spectrometry (NTI-MS). To ensure accuracy, stable chlorine isotope ratios (35Cl/37Cl) were measured using a total evaporation approach on a NIST standard solution, minimizing isotope fractionation. Ba was loaded onto a degassed rhenium filament to enhance ionization, and multi-collector NTI-MS measured 35Cl, 36Cl, and 37Cl simultaneously. The method achieved consistent detection of 36Cl with high reproducibility, demonstrating its suitability for nanogram-level isotope analysis in complex environmental samples.