High-precision analysis of potassium isotopes by MC-ICP-MS without collision cell using cool plasma technique in low resolution mode

This study presents a method for high-precision stable potassium (K) isotope analysis using Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) without collision cell in low resolution mode. Cold plasma technique (RF power is ~600W) combined with wet plasma is used to suppress the formation of argon hydrides, which are direct isobaric interference to K ions. The remain ArH+ interference are deducted by measurements to blank acid before and after each measurement. With the analytical method, precision of better than 0.08‰ (2SD) for 41K/39K could be achieved based on routinely measurements to pure K solution during over six months. Effects of matrix elements, acid strength, ArH+ percentage and concentration mismatch on the precision of K isotope measurement were also evaluated. Mismatches in K concentration (up to 20%) between samples and bracketing standards do not affect the precision and accuracy significantly, while the precision and accuracy are very sensitive to mismatches of acid molarity. Thus, a same batch of acid is needed to dissolve samples and bracketing standards. Measured potassium isotopic compositions of international rock standards using present method agree well within analytical precisions with previous reported values. We believe that this contribution would accelerate the output efficiency of the K isotope data and motivating the use of potassium isotopes as potential tracers in geosciences.