Determination of Stable Chlorine Isotopes by Isotopic Preparative Chromatography (IPC) with Positive–Thermal Ionization Mass Spectrometry (P-TIMS)

A novel approach to chlorine isotope analysis is presented to overcome many drawbacks of existing methods. Contemporary methods often require several laborious off-line procedures prior to instrumental determination; interfering ions (SO42- and NO3-) in real samples are difficult to completely remove, especially when the concentrations of those ions are equal to that of the Cl- ion. This study was aimed to develop an automatic sample preparation method with chromatographic purity for determination of chlorine isotopes using isotopic preparative chromatography (IPC), which was a modified ion chromatograph and a fraction collector. An AS19 chromatographic column was employed to separate chlorine from interference ions using an eluent, flow rate, and suppressor current of 30 mM NaOH, 1 mL/min, and 70 mA, respectively. After the original solutions introduced into the IPC, eluted pure chlorine in the form of HCl was collected in an automated procedure from the outlet of the detector for 6 to 10 mins. The recoveries of chlorine were more than 95% with the relative standard deviation (RSD) of the separation less than 1.8%. After transforming the HCl into CsCl with a resin and concentration in a super-clean laboratory, the samples were sent to the thermal ionization mass spectrometer. The present method was validated by certified reference materials and real samples. The precision of 37Cl/35Cl ratio value was generally below 0.20 ‰. This method provides a potential approach for the analysis of samples with low chlorine concentrations.