Extraction and analysis of hydrosoluble chlorine and its stable isotopic composition in soil using thermal ionization mass spectrometry

Chlorine is an essential micronutrient for high plant growth. The uptake of chlorine by plants is controlled by the hydrosoluble chlorine in soil, which can lead to the cycle change of chlorine isotopes in surficial processes. In this study, a novel method using water extraction coupled with concatenated ion exchange chromatography for the extraction of hydrosoluble chlorine in soil samples is established for the determination of chorine isotopes by thermal ionization mass spectrometry. The results show that no loss of Cl− ion and the fractionation of chlorine isotopes occur in the extraction, with recoveries ranging from 96.4% to 106.4%. The variations of δ37Cl values in soil samples range from −2.40‰ to +1.31‰ with an average of −0.44‰ at a standard deviation of 1.08‰. Stepwise linear regression analysis reveals a positive linear relationship between δ37Cl values and Cl− amount in HT soil profile, which indicates that the diffusion of Cl− ion along with soil water flow controls the chlorine isotope in the range of less than 2‰ in soils. The correlation in WF soils shows that except the seawater invasion, the 37Cl value variation is attributable to the mixing of different sources including anthropogenic activities. [Display omitted] •An effective method for the extraction of hydrosoluble chlorine in soil is developed.•Isotopes of hydrosoluble Cl show specific δ37Cl values in soil samples.•Chlorine amount gradient and δ37Cl values show different sources in soils.•Insight of δ37Cl help us to understand the chemical behaviors of chlorine in soils.