High precision direct analysis of magnesium isotope ratio by ion chromatography/multicollector-ICPMS using wet and dry plasma conditions

Abstract

In this work the applicability of Ion Chromatography (IC) coupled to Multicollector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) for on-line magnesium isotope ratio analysis was explored. Various instrumental setups were employed to enable continuous magnesium separation from the sample matrix by IC followed by MC-ICPMS. The performance of two separation columns IonPac CS16 (ID 5mm or ID 3mm) connected with appropriate CERS 500 suppressors (4mm or 2mm) using dry and wet plasma conditions was compared. With the use of ID 3mm column and 2mm suppressor it was possible to apply dry plasma mode with Aridus II desolvation system. Mass discrimination and instrument drift were corrected by sample-standard bracketing method using the 26Mg/24Mg isotope ratio of DSM-3 as standard. Good accuracy and high precision of the magnesium isotope ratio (generally 0.15‰ (2SD)) were achieved for wet and dry plasma modes; both were comparable to off-line Mg separation and continuous measurement. The sensitivity of MC-ICPMS measurements with dry plasma was 25 times higher in comparison to wet plasma conditions. Robustness and applicability of the method was demonstrated for matrix-rich natural water and rock samples magnesium isotope analysis.