Ne and Ar isotope analysis of samples with high abundance ratios of Ar/Ne and low abundance of Ne by MMS and QMS. Issue 6 (24th April 2019)

• Record Type: Journal Article
• Authors: Junjie, Li; Hanbin, Liu; Jia, Zhang
• Is Part Of: Journal of analytical atomic spectrometry. Volume 34:Issue 6(2019)
• Page Start: 1205
• Page End: 1215
• Publication Date: 2019-04-24
• Subjects: Atomic spectra -- Periodicals; Atomic absorption spectroscopy -- Periodicals; 543.0858
• DOI: 10.1039/c8ja00454d
• Languages: English
• ISSNs: 0267-9477

Abstract

Abstract : Through cryogenic separation by a stainless steel trap, precise Ne and Ar isotope measurement of samples with high abundance ratios of Ar/Ne and extremely low abundances of neon was achieved by a combination of MMS and QMS. Abstract : Analysis of isotopes of neon and argon using the same mass spectrometer is somewhat difficult because the 40 Ar background after argon measurement can interfere with the 20 Ne determination due to the very similar mass-to-charge ratios of 40 Ar ++ and 20 Ne + . Analysis becomes even more difficult if the sample has a high abundance ratio of Ar/Ne and an extremely low amount of Ne. Here, we present a method for precise measurement of neon isotopes on a noble gas mass spectrometer (MMS) and argon isotopes on a quadruple mass spectrometer (QMS). The desorption curves of neon and argon on a charcoal trap and stainless steel trap were respectively determined, and the results demonstrated that the stainless steel trap was more suitable for the absolute separation of neon and argon despite requiring a lower temperature. The argon background effect of the MMS on the 20 Ne determination was discussed emphatically; it was found that the charcoal trap immersed in liquid nitrogen (LN) near the ion source could effectively decrease the argon background. Furthermore, the liquid level of the LN should not only be located as close to the ion source as possible but should be kept constant, which is very important for the measurement of 20 Ne with a small signal size. The ratio of CO2 ++ /CO + for MMS was 1.2 ± 0.3%, which enabled the correction of CO2 ++ interference in the 22 Ne determination. An artificial mixture of standard gases with an abundance ratio of argon to neon as high as 1000 was prepared. 0.1 cm 3 standard gas mixture with 5.50 × 10 −13 mol argon and 5.53 × 10 −16 mol neon was measured each time. The precisions of the isotopic ratios of neon measured by MMS were ±0.15% for 20 Ne/ 22 Ne and ±1.6% for 21 Ne/ 22 Ne. The precisions of the isotopic ratios of argon measured by QMS were ±0.5% for 40 Ar/ 36 Ar and 4.0% for 38 Ar/ 36 Ar. Although the precision of the argon isotope analysis obtained by QMS was not as good as that obtained by MMS, it fully meets the requirements for application in geochemical tracers. Moreover, this method avoids the use of the same mass spectrometer for analysis of both argon and neon, thus guaranteeing precision of the neon isotope measurements.