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

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 5 mm or ID 3 mm) connected with appropriate CERS 500 suppressors (4 mm or 2 mm) using dry and wet plasma conditions was compared. With the use of ID 3 mm column and 2 mm 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‰ (2 SD)) 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.