Nano-particulate pressed powder pellets: multi-method homogenous MRMs for in situ analysis with high spatial resolution

The quality of in-situ micro-analytical data relies on the availability and use of sufficiently matrix-matched reference materials. Their physical and chemical properties have to meet the requirements of analytical instrumentation, e.g., withstand high-vacuum and impact of high-energy laser, electron, and ion beams, they have to be stable over time and under various environmental conditions, certified following ISO guidelines, and available for a wide variety of compositions matching the unknown samples. Homogeneity of pulverized pressed materials is a function of both sampled volume and grain size and must allow elemental and isotope analysis with high spatial resolution <10-32μm as required in imaging applications or mineral analysis. We developed a method for manufacturing undiluted, binder-free pressed powder pellets[1] with particle grain size down to the nanometer range (D50 <170 nm) that meet the above requirements, have extremely low roughness RA < 50 nm of pellet surface, and excellent within and between pellet homogeneity.
This technique has been applied so far to a wide range of very different sample types: biogenic carbonates (foraminifera, clam shells, algae, coral), speleothem, silicate rocks, iron ores and banded iron formation, manganese nodules, sulphides UQAC-FeS, refractory minerals, plutonic and volcanic rocks, fly ash, bone-apatite, minerals for Rb/Sr age-dating[2] etc.
We successfully tested blending of different materials opening new ways for producing e.g., series of elemental and isotopic calibration standards. These “nanopellets” have been used with LA-ICP-MS, LIBS, µ-XRF, handheld-XRF instruments, and also with EPMA, PIXE, SIMS making them a new and, possibly, universal matrix-matched MRM. They have the potential of replacing time-consuming, hazardous and tedious acid digestion procedures. Here we give an overview of the present state of development of new MRM[3] and their characterization in terms of grain size distribution, surface topography, porosity, homogeneity, and accuracy of analytical results for both elemental (major, minor, trace and ultra-trace elements) and isotopic (Sr, Li, B, O) composition.