K isotope analysis using total evaporation method

Abstract

We are developing ⁴⁰K-⁴⁰Ca dating technique for authigenic illite and other materials in fault rocks as a new dating method to constrain the age of fault activity. In ⁴⁰K-⁴⁰Ca dating, quantities of potassium and calcium are determined by isotope dilution thermal ionization mass spectrometry. In this study, a total evaporation method was considered for the determination of potassium spike and isotope analysis, and a preliminary analysis of a reference material (Alfa Aesar) was performed.9 samples were analyzed without activator and with about 0.5 ng of potassium loading, yielding ³⁹K/⁴¹K=13.8580±0.0090 and ⁴⁰K/⁴¹K=0.000127106±0.000007437 (n=9, 2SD). Although the results are not significantly different from the natural isotopic composition, the standard deviation is large in the isotopic ratio with ⁴⁰K, which is less abundant. It is considered that ⁴⁰Ca due to filaments and other factors have affected the integrated value of ⁴⁰K. Reduce the influence of interference by using filaments of high purity and ensuring an analysis time of about 1 hour per sample.