Measurement of chlorine stable isotopic composition by negative thermal ionization mass spectrometry using total evaporation technique

Abstract

NOTE241 measurement. Even the P-TIMS method requires microgram quantity of Cl for precise analysis. For this reason, these two methods have been applied to the isotopic analysis of relatively large samples, or samples with high Cl concentration such as fluid inclusion in ore deposits (Eastoe and Guilbert, 1992), evaporites (Eggenkamp et al., 1995), Cl-bearing silicate minerals (Willmore et al., 2002) and Cl-rich metamorphic rocks (Barnes and Sharp, 2006;Bonifacie et al., 2008). The N-TIMS technique, on the other hand, provides much higher sensitivity for chlorine relative to IRMS and P-TIMS, and only several hundred nano-grams of Cl is necessary (Fujitani and Nakamura, 2006). However, its analytical precision is worse than the former two methods mainly due to the effect of isotopic fractionation during the evaporation and ionization processes (normally in the order of few ‰).Previous studies have demonstrated the existence of large isotopic fractionation of chlorine during geological process (Stewart and Spivack, 2004;Godon et al., 2004). If the precision of Cl isotopic analysis for the N-TIMS can be improved, it will provide the opportunity to investigate the chlorine isotopic composition of small samples that cannot be studied with the IRMS and P-TIMS methods. One candidate to improve the precision for N-TIMS Measurement of chlorine stable isotopic composition by negative thermal ionization mass spectrometry using total evaporation technique A total evaporation negative thermal ionization mass spectrometry (TE-N-TIMS) technique for the isotopic analysis of chlorine was developed. This technique provides fast and reliable way to determine the isotopic signature of chlorine samples as small as 100 ng. Compared to the conventional N-TIMS method, the precision of the Cl isotopic analysis is improved by a factor of up to 3 by minimizing the effect of mass fractionation. Using this method, reproducibility of 0.9‰ (R.S.D.: n = 25) can be achieved for 37 Cl/ 35 Cl ratio of 200 ng Cl. The analyzed results of the AgCl reagent expressed as a per-mil deviation (δ 37 Cl) relative to the Standard Mean Ocean Chloride showed good concordance with the value obtained by conventional positive thermal ionization mass spectrometry (P-TIMS).

Studies on Isotope Ratio Measurement of Cl by Inductively Coupled Plasma Triple-quad Mass Spectrometry

“…Though the present study is out of scope for the isotope ratio measurements with high precision (0.005 -0.0001% of relative standard deviation, RSD) which is expected by IRMS 35,36 and TIMS, 37,38 it is expected to be applicable to the studies for stable isotope tracers, 1 H and 36 …”