Christoph Neff

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Neff

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Christoph

ORCID

0000-0002-9369-9580

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Publications1 - 10 of 10

Failed genesis of a Fe-skarn deposit caused by redox states of intrusion and wall rocks (Torre di Rio, Island of Elba, Italy)
Garofalo, Paolo S.; Redi, Daniele; Malafeevskiy, Nikita; et al. (2025)
Ore Geology Reviews
The Torre di Rio skarn (Island of Elba, Italy) is a pyroxene-ilvaite-epidote skarn that hosts a Fe-oxide mineralization and is the type locality of the mineral ilvaite. In contrast with other Fe deposits of the island, it belongs to a group of subeconomic skarns. We combine surface mapping, petrographic data, scanning electron microscope and electron probe microanalyses, fluid inclusion microthermometry, elemental imaging by Laser Ablation-Inductively Coupled Plasma - Time of Flight Mass Spectrometry (LA-ICP-TOFMS), and fluid-mineral equilibria to compare the genesis of this skarn with that of typical economic skarns. Fieldwork shows that Torre di Rio consist of ilvaite-, ilvaite-pyroxene, and pyroxene-epidote zones. The epidote-rich zone is in contact with the wall rocks, i.e., a sequence of pelites, marls, marbles, and other sedimentary lithologies. The 6.53–5.9 Ma Porto Azzurro monzogranite is the reduced (ilmenite-bearing) causative intrusion of the skarn, which induced contact metamorphism in the wall rocks at 6.7–6.2 Ma. Torre di Rio formed within the biotite-white mica-chlorite metamorphic zone, a few hundred meters from the contact with Porto Azzurro. Within the skarn, ilvaite and pyroxenes are both euhedral and arranged in rosettes and spheroids. Ilvaite has a consistent chemical composition with a significant Mn enrichment close to the wall rocks, and pyroxene is hedenbergitic. The epidote is euhedral and occurs as epidote s.s. and allanite-(Ce). Late phases are albite, annite, phengite, chlorite, quartz, calcite, and chalcedony. Magnetite and hematite form spheroid textures or are finely mixed. Euhedral pyrrhotite and pyrite host native Bi and Pb. Seventeen calcite- and quartz-hosted fluid inclusion assemblages from the ilvaite skarn zones are associated with the magnetite and hematite aggregates. At room temperature, all assemblages are two-phase (L-V). Fourteen of them show constant phase proportions and three show variable proportions. The assemblages with constant phase proportions have salinities between 0.8 and 17.0 mass% NaCleq and homogenize by bubble disappearance between c. 150 and 300 °C. The assemblages with variable phase proportions homogenize by bubble and liquid disappearance between 280 and 330 °C. Element imaging by LA-ICP-TOFMS of ilvaite and quartz from skarn spheroids shows that several lithophile (e.g., Al, Mg) and siderophile (e.g., As, Ge, Ga, In, Sb) trace elements occur at concentrations between c. 20 μg/g and 1 wt%. We interpret our dataset as a product of a shallow skarn that formed under extremely reducing conditions, which were controlled by the redox nature of both Porto Azzurro and wall rocks. At these conditions, supersaturation of pyroxenes and ilvaite within the skarn was achieved as a result of phase separation, cooling, and mixing of batches of heterogeneous and homogeneous ore fluids at about 350–150 °C. A Fe-skarn deposit failed to form at Torre di Rio because the supersaturation of Fe-oxides from the ore fluid was inhibited, but the presence of the typical siderophile elements of geothermal-epithermal deposits indicate that the ore environment was transitional between skarn and epithermal. Similar conditions are found in other deposits of the Island of Elba and of the Northern Apennine belt.
Scallop shells as biosorbents for water remediation from heavy metals: Contributions and mechanism of shell components in the adsorption of cadmium from aqueous matrix
Chenet, Tatiana; Schwarz, Gunnar; Neff, Christoph; et al. (2024)
Heliyon
To ascertain their potential for heavy metal pollution remedy, we studied the adsorption mechanism of cadmium onto scallop shells and the interactions between the heavy metal and the shell matrix. Intact shells were used to investigate the uptake and diffusion of the metal contaminant onto the shell carbonatic layers, as well as to evaluate the distribution of major and trace elements in the matrix. LA-ICPMS measurements demonstrate that Cd is adsorbed on a very thin layer on the inner and outer surfaces of the shell. Structural and thermal analyses showed the presence of 9 wt.-% of a CdCO₃ phase indicating that the adsorption is mainly a superficial process which involves different processes, including ion exchange of Ca by Cd. In addition, organic components of the shell could contribute to adsorption as highlighted by different metal uptake observed for shells with different colours. In particular, darker shells appeared to adsorb more contaminant than the white ones. The contribution of the organic shell components on the adsorption of heavy metals was also highlighted by the element bulk content which showed higher concentrations of different metals in the darker specimen. Raman spectroscopy allowed to identify the pigments as carotenoids, confirmed by XRD measurements which highlighted the presence of astaxanthin phases. The results presented here provide new insights into the Cd adsorption mechanism highlighting the important contribution given by the organic components present in the biogenic carbonate matrix. Furthermore, the high efficiency of Cd removal from water by scallop shells, supported by adsorption kinetic and isotherm studies, has been demonstrated.
Colloidal CsPbX3 Nanocrystals with Thin Metal Oxide Gel Coatings
Guggisberg, Dominic; Yakunin, Sergii; Neff, Christoph; et al. (2023)
Chemistry of Materials
Lead halide perovskite (LHP) nanocrystals (NCs) have gathered much attention as light-emitting materials, particularly owing to their excellent color purity, band gap tunability, high photoluminescence quantum yield (PLQY), low cost, and scalable synthesis. To enhance the stability of LHP NCs, bulky strongly bound organic ligands are commonly employed, which counteract the extraction of charge carriers from the NCs and hinder their use as photoconductive materials and photocatalysts. Replacing these ligands with a thin coating is a complex challenge due to the highly dynamic ionic lattice, which is vulnerable to the commonly employed coating precursors and solvents. In this work, we demonstrate thin (<1 nm) metal oxide gel coatings through non-hydrolytic sol-gel reactions. The coated NCs are readily dispersible and highly stable in short-chain alcohols while remaining monodisperse and exhibiting high PLQY (70-90%). We show the successful coating of NCs in a wide range of sizes (5-14 nm) and halide compositions. Alumina-gel-coated NCs were chosen for an in-depth analysis, and the versatility of the approach is demonstrated by employing zirconia-and titaniabased coatings. Compact films of the alumina-gel-coated NCs exhibit electronic and excitonic coupling between the NCs, leading to two orders of magnitude longer photoluminescence lifetimes (400-700 ns) compared to NCs in solution or their organically capped counterparts. This makes these NCs highly suited for applications where charge carrier delocalization or extraction is essential for performance.
Fluid-rock interaction, skarn genesis, and hydrothermal alteration within an upper crustal fault zone (Island of Elba, Italy)
Garofalo, Paolo S.; Maffei, Jacopo; Papeschi, Samuele; et al. (2023)
Ore Geology Reviews
The Terranera magnetite-hematite-pyrite deposit of the Island of Elba (Italy) is an historical skarn deposit hosted by a fault zone of regional importance (Zuccale Fault) and by its hanging wall rocks. We combine field observations with petrographic data, electron probe microanalyses (EPMA), XRPD data, fluid inclusion microthermometry, and element imaging by Laser Ablation-Inductively Coupled Plasma-Time of Flight Mass Spectrometry (LA-ICP-TOFMS) to define the ore-forming process at Terranera. We show that in this location the fault is made of four levels of mineralized fault rocks having distinct mineral compositions. In these levels, a mineral association made of diopside, clinozoisite, and other Mg-rich minerals is replaced by magnetite, hematite, pyrite, Mg-hornblende, clinochlore, and other Mg-rich phyllosilicates. This paragenesis is overprinted by goethite and clay minerals. Chlorite-quartz geothermometry and fluid inclusion microthermometry show that ore precipitation occurred at 350–180 °C from fluids of distinct bulk salinities, but goethite and clay mineral overprinting progressed at lower T. We propose that Terranera is a magnesian Fe skarn formed due to the interaction between distinct hydrothermal fluids and a dolomitic protolith, which was preserved within the fault zone. These fluids mixed and cooled during protolith metasomatism, causing ore precipitation due to oxidation and desulfidation. A very similar process was described in a large deposit of Elba (Rio Marina). Argillic alteration was widespread within the fault but met permanently intermediate sulfidation conditions. Trace element composition of hematite shows that Terranera has features that overlap those of skarn and epithermal deposits. In particular, elements that are typical of epithermal deposits (Sb, Ga, Ge, As) occur at mass fractions (50–200 μg/g) that are either unreported or not typical of hematite from skarn deposits. These features identify Terranera as formed in an ore environment that was transitional between that of a skarn and of an epithermal deposit. These features are shared by other historical deposits located at Elba and in the massive pyritic ore district of south Tuscany (e.g., Gavorrano, Fenice Capanne). This indicates that a similar environment might have occurred during the Neogene beyond Elba, in a much larger ore district of south Tuscany.
Differential allocation of cadmium and zinc in durum wheat during grain filling as revealed by stable isotope labeling
Yan, Bofang; Nguyen, Christophe; Cornu, Jean-Yves; et al. (2023)
Plant and Soil
Background and aims Cereals can be made safer and more nutritious by reducing cadmium (Cd) and enhancing zinc (Zn) levels. To respectively regulate the accumulation of these chemically similar ele- ments in grains, it is essential to understand the dif- ferences between Cd and Zn allocation to grains. Methods In durum wheat (Triticum durum), dual- isotope ( 111Cd and 67Zn) labeling was used to trace the post-anthesis uptake fluxes separately from the remobilization of pre-anthesis vegetative pools. Laser ablation inductively coupled mass spectrometry was used to investigate the spatial distribution of Cd and Zn in the uppermost node. Results Among the shoot organs, both pre- and post-anthesis derived Cd was more allocated to the high-transpiring organs (i.e., bracts and flag leaves) whereas Zn was more to the grain. Cadmium was likely less efficiently transferred from the xylem to the phloem as suggested by the elemental maps which showed that Cd was more abundant than Zn in the xylem of the uppermost node. Furthermore, unlike Zn, Cd was not significantly remobilized from the high-transpiring organs, which further limited the allocation of Cd to the grain. Conclusion High-transpiring organs are sources of grain Zn but irreversible sinks of Cd. Agronomic strategies that enhance Cd sequestration and Zn remobilization in high-transpiring organs could con- tribute to producing grains with low Cd and high Zn concentrations.
Technological developments for controlled, faster and cost-effective LA-ICP-MS
Neff, Christoph (2022)
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is an established element analysis technique and can provide the element composition and concentration of solid materials from major to trace elements. In combination with spatial resolved sampling called element imaging, the element distribution can be accessed. In earth science, spatially resolved element analysis of minerals and rocks can give insights into geological processes and contribute to the understanding of the genesis. Especially the combination of small volume, low dispersion, fast washout ablation cells and the inductively coupled plasma time-of-flight mass spectrometer (ICP-TOFMS) significantly extended the gain of information from the element imaging analysis. Fast washout ablation cells deliver high density aerosol packages and short signals. This increases the signal to noise ratio and therefore improves the limit of detection. This allows to apply small laser spots for high resolution analysis with still sufficient sensitivity. The fast detection of the ICP-TOFMS allows to detect the full element mass spectrum quasi-simultaneously at high frequency. The acquisition of the full element mass spectrum gives the full picture of element distributions. Often, it allows also to uncover unexpected incorporation of elements into minerals as there is no need to limit the pallet of analytes. The delivery of high density aerosol packages and the high frequency detection allow to measure individual laser pulses and sample positions without aerosol mixing. A high sampling frequency is of major importance for element imaging to be applicable, as often hundreds of thousands of sample position are required for an analysis. In this thesis, the focus was on extending the applicability of LA-ICP-TOFMS element imaging. In Chapter 2 a new configuration of a fast washout ablation cell is presented and investigated. The parallel flow ablation cell (PFAC) is a modification of the tube cell design and provides shortest signal duration published so far. It provides further advantages compared to other fast washout ablation cell as for example a larger inner cell to sample surface distance (CSD) and a higher tolerance to variations in the CSD to achieve shortest signal durations. The short and reproducible signals revealed a present mass dependent shift of ion transport from light to heavy ions. A collision and reaction cell filled with H2 slightly reduced the mass dependent shift but did not allow to fully correct the different traveling speeds by collisional cooling. The fast and robust washout in a wide range of CSD makes the PFAC a promising ablation cell to increase the speed for element imaging analysis while maintaining the possibility for pulse-to-pulse signal separation. In Chapter 3 the first study of a nitrogen based inductively coupled plasma mass spectrometry system in conjunction with laser ablation (LA-(N2-ICP)-MS) is evaluated. N2 as the plasma gas has the potential to remove Ar plasma species leading to less interferences and to reduce the costs of the gas supply. The built prototype instrument achieved similar sensitivities compared to LA-(Ar-ICP)-MS. Ar plasma species were strongly reduced and nitrogen plasma species were more pronounced. The limits of detection for LA-(N2-ICP)-MS and LA-(Ar-ICP)-MS were similar or even lower for most elements using LA-(N2-ICP)-MS. Glass reference materials were quantified and could be determined within the uncertainty of the reference values. Overall, the nitrogen plasma source coupled to a mass spectrometer could challenge the argon-sustained ICP-MS in element analysis in the near future. In Chapter 4 an imaging control system (ICS) is presented and its capabilities are demonstrated. It synchronizes the control of the sample translational stage, the laser and the TOFMS data acquisition. This allows a virtually automated data acquisition. The triggered data acquisition for every ablation position leads to binned pixel data in relation to the sample position. This simplifies and reduces the time for data evaluation. Different imaging modes can be applied and allow for example the ablation of a custom shaped ablation area or to analyze a large area in multiple sections. Ablation modes can be applied according to the application. A single pulse mode allows the fast scanning of the area of interest or a hole-drilling mode provides higher pixel sensitivity and lower limits of detection while maintaining the same lateral resolution. A surface cleaning pulse can be applied at every sample position to reduce the influence of surface contamination and redeposited material from previous ablation spots. Overall, in this thesis the applicability of LA-ICP-TOFMS element imaging was extended by improving the reliability of the analysis system, extending the capabilities for further applications and reducing the costs for the analysis.
Parallel flow ablation cell for short signal duration in LA-ICP-TOFMS element imaging
Neff, Christoph; Becker, Pascal; Günther, Detlef (2022)
Journal of Analytical Atomic Spectrometry
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 can be carried out. Here, we introduce a modified ablation cell based on the tube cell design for laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) element imaging which provides shorter signal durations. The parallel flow ablation cell (PFAC) included a recess in the cover for improved gas flow pattern at the ablation site and achieved signal durations of 0.25 ms (FW0.1M) for 44Ca and 0.29 ms (FW0.1M) for 238U on NIST SRM 610 using a laser ablation repetition rate of 100 Hz. Shortest signal duration was achieved using an inner cell to sample surface distance (CSD) of 700 μm, which is several times larger compared to previous fast washout ablation cells published and shows high tolerance to variations in the CSD. A shift in arrival time from the ablation to TOFMS extraction was observed when comparing light to heavy ions. A H2 collision and reaction cell was not able to correct for this shift and lead to extended signal durations, but still very short signals of approximately 0.4 ms (FW0.1M) were observed. The robustness of the washout in a wide range of CSD makes the PFAC a promising ablation cell for fast aerosol transport and quasi-simultaneous detection of ions using an ICP-TOFMS and element imaging using a ≥1000 Hz laser ablation rate while maintaining the possibility for pulse-to-pulse signal separation.
Capabilities of Automated LA-ICP-TOFMS Imaging of Geological Samples
Neff, Christoph; Keresztes Schmidt, Peter; Garofalo, Paolo S.; et al. (2020)
Journal of Analytical Atomic Spectrometry
Element imaging aims to provide quantitative data on multi-element distributions from major to trace elements with high lateral resolution. Here, we describe a control system for laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) imaging with complex integration of translational stage, laser, and mass spectrometer data acquisition which was tested on glass and mineral samples. In particular, besides single pulse imaging at a laser repetition rate of 100 Hz using a 5 μm laser spot size, a hole drilling imaging approach provided higher pixel sensitivity and lower limits of detection (<1 mg kg−1 for most heavy elements) while maintaining the same lateral resolution. An optional surface cleaning pulse can be applied without additional recording of data. Furthermore, the ablation area can be adapted to specific object structures of interest and leads to significant shorter imaging times. Triggering the data acquisition for every ablation position led to binned pixel data in relation to the sample position. This simplifies the data evaluation and allows a more automated image generation. The approach presented in this study enables flexible adjustments of distinct ablation modes to a specific analytical task and provides the basis for fully automated element imaging. To test the applicability of our approach, two complex geological samples containing crystalline solids were imaged to gain insights into the distribution of trace elements that occur typically in the low mg kg−1 range. We show that both single pulse and hole drilling ablation modes allow the determination of a large number of trace elements. However, the hole drilling mode shows a superior sensitivity per pixel, which in turn provides more detailed information about the formation of geological samples.
LA-ICP-MS using a nitrogen plasma source
Neff, Christoph; Becker, Pascal; Hattendorf, Bodo; et al. (2021)
Journal of Analytical Atomic Spectrometry
Here we describe the first study of a nitrogen based inductively coupled plasma mass spectrometry system in conjunction with laser ablation (LA-(N-2-ICP)-MS). Therefore, a microwave-sustained, inductively coupled, atmospheric-pressure plasma source was mounted onto the interface of a quadrupole ICP-MS to investigate the capabilities of such an instrument. The proof of concept study was focused on the quantification capabilities of major to trace elements. Therefore, the plasma background species under dry plasma conditions were investigated to identify the most suitable isotopes for the analysis and to describe the newly formed nitrogen plasma interferences. In addition, the instrumental drift was investigated. Selected elements in the reference materials NIST SRM 612 and BCR-2G were quantified using NIST SRM 610 as an external standard and could be determined within the uncertainty of the reference values. Finally, the limits of detection for LA-(N-2-ICP)-MS and LA-(Ar-ICP)-MS were compared indicating similar or even lower LODs for most elements using LA-(N-2-ICP)-MS. Therefore, a nitrogen plasma source coupled to a mass spectrometer could challenge the argon-sustained ICP-MS in element analysis by overcoming argon interferences and has the potential to reduce the plasma gas expenses significantly.
Forensic Float Glass Fragment Analysis Using Single-Pulse Laser Ablation Inductively Coupled Plasma Time of Flight Mass Spectrometry
Becker, Pascal; Neff, Christoph; Hess, Sabine; et al. (2020)
Journal of Analytical Atomic Spectrometry
The most discriminating method that is currently applied in routine forensic elemental analysis of glass is laser ablation in combination with quadrupole or sector field based inductively coupled plasma mass spectrometry (LA-ICPMS) following the standard method ASTM E2927-16E1. Due to the sequential measurement method, sample size constraints of approximately 400 μm × 200 μm × 100 μm with six individual measurements have been reported to provide optimum parameters for glass discrimination. The necessary sample size is given by the spot size, number of laser pulses per replicate and number of replicate measurements. In this study, a single-pulse laser ablation inductively coupled plasma time of flight mass spectrometry (Single-Pulse LA-ICP-TOFMS) method was developed and applied for the matching and mismatching of forensic float glass evidence. 110 laser pulses with an ablation spot diameter of 90 μm were applied to float glass fragments of a size below 400 μm in diameter. 18 elements were quantified from each individual laser pulse in order to compare the corresponding concentrations between various glass fragments. In contrast to previous work, a modified 5-sigma criterion was used to successfully match fragments from the same source and mismatch fragments from differing sources. The data set generated within this study demonstrates new capabilities when using quasi simultaneous signal detection and reduced the necessary sample volume from 400 μm × 200 μm × 100 μm to 100 μm × 100 μm × 33 μm, which corresponds to a reduction in sample material from 20 μg to 0.8 μg. The proof of concept is shown for the application of a single-pulse based method for glass fragment analysis in a forensic context, which would allow the measurement of smaller fragments than previously possible.

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