Combining standard addition and isotope dilution in order to improve SI traceable LA-ICP-MS measurements

Abstract

Laser ablation (LA) combined with inductively coupled plasma mass spectrometry (ICP-MS) is a common method for analysing non-matrix elements in solid samples directly. Although LA was significantly improved over the last years, SI traceable quantification is still challenging. Therefore, LA-ICP-MS was combined with isotope dilution (ID) in this work. Through the SI traceable solutions and the known reference element content in the sample itself, it is possible to calculate a traceable mass fraction for the analyte element with an uncertainty budget according to the “Guide to the Expression of Uncertainty in Measurements” (GUM). For this new approach, two concentration series – one for the analyte and the other for the reference element – are necessary. These solutions were varied with respect to their isotope ratios. Some instrumental effects like successive clogging of a valve or tube will have a direct influence on the intensity. However, there will be no impact on the measured isotope ratio. The series of solutions have been introduced sequentially into the plasma simultaneously with the ablated material via a y-piece. To show that reliable results can be achieved with the new method, boron was quantified in a glass-based standard reference material (NIST SRM 612). The information value of 32 μg g⁻¹ could be reproduced as (33.3 ± 3.7) μg g⁻¹ nearly perfectly. Compared with the SI traceable LA-ICP-MS measurement [L. Michaliszyn, T. Ren, A. Röthke and O. Rienitz, J. Anal. At. Spectrom., 2020, 35, 126–135], the result is more accurate and has a lower measurement uncertainty (k = 2).