Potassium
isotopic analysis is arousing increasing interest, not
only in geochemistry, but also in biomedicine. However, real-life
applications are still hindered by the lack of robustness of the methods
used. In this work, a novel and robust method for high-precision K
isotopic analysis of geological and biological samples was developed,
based on the use of a multicollector ICP-mass spectrometer providing
a mass resolving power of 15,000 (extra-high resolution mode, XHR).
After evaluation of different measurement conditions, i.e., hot vs cold plasma conditions, standard-type vs jet-type sampling cone, and high resolution (HR) vs XHR, a combination of hot plasma conditions, use of the
high-transmission jet-type sampling cone, and the XHR mode allowed
for high-precision and interference-free K isotopic analysis. Potassium
signal monitoring was performed in the ArH+ interference-free
0.006–0.007 amu wide peak shoulder using the XHR mode. The
within-run, short-term external, and long-term external precisions
for the δ41K value were 0.02‰ (2se, N = 50), 0.03‰ (2SD, N = 7), and
0.06‰ (2SD, N = 163), respectively. A two-stage
chromatographic procedure was developed for the isolation of K from
both geological and biological samples, and potential matrix effects
affecting the K isotope ratio were systematically evaluated. The method
was first applied to geological reference materials (RMs) for validation
purposes, and the K isotope ratio results were in good agreement with
those previously reported. Subsequently, a series of biological RMs,
including serum, whole blood, cerebrospinal fluid, bovine muscle,
and lobster hepatopancreas, were characterized for their K isotopic
composition.
