Effects of operating conditions and matrix on mass bias in MC-ICPMS

Abstract

Isotope ratio measurements by multicollector inductively coupled plasma mass spectrometry are affected by mass bias, the mass-dependent sensitivity of the isotopes. This study evaluates the variation of mass bias on different instrumental parameters such as the carrier gas flow rate, the sampling depth in the plasma as well as the ion optic settings. Differences and similarities are shown between the isotope ratio variation profiles for liquid sample introduction by solution nebulization only and for membrane desolvation. They are assigned to the different behaviour of their resulting aerosols in the plasma. A promising approach towards stabilization of mass bias by measuring at elevated carrier gas flow rates is shown. Operation at 60% sensitivity reduced the bias on ¹⁴⁶Nd/¹⁴⁴Nd introduced by a matrix of 10 µg/g Ho up to six times compared to the highest sensitivity conditions.