Suitability of Mn- and Fe-rich reference materials for microanalytical research

Manganese- and iron-rich materials are of major geoscientific and economic interest, many of which contain microscopic features that provide valuable information. To obtain accurate results, a homogeneous microanalytical reference material for calibration is needed. Several researchers have used the Mn- and Fe-rich RMs, JMn-1, NOD-A-1, NOD-P-1 and FeMn-1, for this purpose; therefore, they were tested in this study to determine their suitability for microanalysis. Their homogeneity was investigated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) with two different types of lasers (nano- and femtosecond), with spot and line scan analyses and with different operating parameters, such as spot size, pulse repetition rate and fluence. As the established manganese nodule RMs revealed inhomogeneities for picogram to microgram test portions, we also investigated the new synthetic Fe- and Mn-rich RM, FeMnOx-1. FeMnOx-1 was found to be homogeneous for large (ø 40 μm: 2% RSD repeatability) and small (ø 8–10 μm: 10% RSD repeatability) spot sizes. This homogeneity is in the range of the homogeneous NIST SRM 610 and GSE-1G reference glasses. Furthermore, FeMnOx-1 revealed a large-scale homogeneity within uncertainties of a few per cent, using test portions in the ng range, when measuring four individual mounts of this material.