Garnet is one of the most robust and ubiquitous minerals that record element zoning during crustal metamorphism. In addition to major elements, zoning in trace elements can provide a wealth of information to document the changing conditions of garnet growth and modification. However, mapping trace elements at low concentrations, over large areas and with high resolution has remained a major challenge.We present a comprehensive investigation of the TE distribution in garnet from three Alpine samples that underwent a complex evolution at different metamorphic conditions. The TE distribution in garnet grains is mapped in 2D in thin section with a novel approach using laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOFMS) to achieve a lateral resolution of 5 µm and limits of detection for the heavy rare earth elements (REE) down to 0.2 µg/g. Comparison with major element zoning measured by electron probe micro-analysis (EPMA) and trace elements measured by conventional LA-ICPMS spot analysis testifies to the accuracy of the measurements.Garnet in an amphibolite-facies metapelite from Campolungo, Central Alps that recorded metamorphism to 600°C preserves Y+REE trace element zoning that closely matches that of Ca. In this sample, there is no notable diffusive modification for trace elements. Y+REE zoning is dominated by Rayleigh fractionation in the core and by the sporadic breakdown of accessory phases producing annuli in the rim of the garnet.A granulite-facies garnet from Malenco, Eastern Central Alps, formed during subsolidus heating, followed by peritectic melting reactions up to temperatures of 800-850°C. Major and trace element zoning are decoupled indicating diffusional resetting of major elements, whereas trace elements still largely document the growth history. Enrichment of trace elements in the garnet mantle may be related to the consumption of biotite (V, Cr) and the dissolution of zircon (Zr) and monazite (Y+REE) in the melt. Diffusion of Y+HREE at the core-mantle boundary occurred over a length scale of ~200 µm.Garnet in an eclogite from the Sesia Zone, Western Alps (P~2 GPa, T~600°C) displays pronounced fluid-related veinlets, visible in FeO, MgO and MnO, which cross-cut the primary growth zoning. Surprisingly, complex Y+REE and Cr zoning is not affected by the veinlets, indicating that they did not form by a crack-seal mechanism but are rather related to a selective replacement process.The trace element maps provide a detailed insight into the growth and modification of garnet and thus allow assessment of equilibrium versus disequilibrium processes, and assist in determination of P-T conditions, garnet dating, diffusion modelling as well as documenting fluid-induced modifications.

A new software control system enables adaptable and task-specific ablation modes for LA-ICP-TOFMS imaging.

The acquisition speed in laser ablation inductively coupled plasma mass spectrometry element imaging depends significantly on the laser aerosol transport system. The faster the aerosol washout, the faster the acquisition...

Here we describe the first study of a nitrogen based inductively coupled plasma mass spectrometry system in conjunction with laser ablation (LA-(N2-ICP)-MS). Therefore, a microwave-sustained, inductively coupled, atmospheric-pressure plasma source...

The application of nanobodies as binding partners for structure stabilization in protein X-ray crystallography is taking an increasingly important role in structural biology. However, the addition of nanobodies to the crystallization matrices might complicate the optimization of the crystallization process, which is why analytical techniques to screen and characterize suitable nanobodies are useful. Here, we show how chemical cross-linking combined with high-mass matrix-assisted laser/desorption ionization mass spectrometry can be employed as a fast screening technique to determine binding specificities of intact nanobody•membrane protein complexes. Titration series were performed to rank the binding affinity of the interacting nanobodies. To validate the mass spectrometry data, microscale thermophoresis was used, which showed binding affinities of the stronger binding nanobodies, in the low μM range. In addition, mass spectrometry provides access to the stoichiometry of the complexes formed, which enables the definition of conditions under which homogeneous complex states are present in solution. Conformational changes of the membrane protein were investigated and competitive binding experiments were used to delimit the interaction sites of the nanobodies, which is in agreement with crystal structures obtained. The results show the diversity of specifically binding nanobodies in terms of binding affinity, stoichiometry, and binding site, which illustrates the need for an analytical screening approach.