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Laser Ablation – Quadrupole-Inductively Coupled Plasma – Mass Spectrometry (LA-Q-ICP-MS) at the GeoZentrum Nordbayern

The GeoZentrum Nordbayern (Fachgruppe Krustendynamik) of the University Erlangen-Nürnberg possesses an Excimer Laser Ablation Unit (TELEDYNE) coupled with an Agilent 7500c Q-ICP-MS. The LA-Q-ICP-MS is used for a variety of applications in earth-, material-and archaeological sciences.

Laser ablation is the most versatile in-situ solid sampling technique for ICP-MS. The focusing characteristics of the laser allows investigations of small areas, local microanalysis and spatially resolved studies of nearly all materials. The signal intensity is directly proportional to the amount of the ablated material which is transported to the ICP-MS. Laser generated signals are transient, the time resolved analysis mode however allows the evaluation of every single part of the signal, even if it is a lateral profile of a depth profile data acquisition.

Quantification of the signals occurs via standard reference material (e.g. NIST 610, NIST 612, NIST 614, Laflamme Po724 B2, (Fe, Ni)1-xS, Mass1, GSE-1G, UQAC-FeS-1, MUL-ZnS ). Repeated standard measurements are conducted throughout a measuring day for correcting an instrumental drift. In order to determine the reproducibility and the accuracy of the method so called ‚secondary‘ standards are ablated.

Laser Ablation

REM-image with a cross section of a 100 micron wide and 140 micron deep laser crater in AlN-ceramics with a nearly ideal flat bottom.

The Teledyne Photon Machines Analyte Excite is a 193nm excimer Ar-F laser system that is equipped with a Helex-II ablation cell and its unique adaptive inner cell. He 5.0 is used as carrier gas and is mixed with Ar 5.0 before entering the ICP-MS. Ablation patterns can be varied (single spot, line of spots, line, raster etc.) as well as the diameter of the laser beam (up to 155µm circle or square) and the repetition rate (up to 100 Hz) according to the respective application. Different light sources (transmitted/coax/ring) for sample illumination and a micron adjustable stage permit extremely precise micro-sampling.

 

QuadrupoleInductively Coupled Plasma Mass Spectrometry

Sample introduction from the laser ablation unit to the ICP-MS occurs via a tygoon tube. A high temperature argon plasma dissociates, atomizes and ionizes the sample to produce a cloud of positively charged ions. The sample ions are extracted from the plasma and passing through the sample and skimmer cones into the mass spectrometer. The Agilent 7500c has a triple-stage vacuum system with a rotary pump for the expansion region (interface) and two turbo-molecular pumps for the intermediate and analyzer stages. The ion optic lens system can be adjusted manually to provide optimum ion transmission and high signal sensitivity. The installed Octopole Reaction System is not exerted because of the short signals. Ions are focused through the quadrupole mass analyzer, where they are separated on the basis of their mass-to-charge ratio (m/z) by varying the RF and DC voltages. These voltages are ramped very rapidly so the quadrupole can scan the whole mass range (2-260 amu) in 100 msec. As a result, spectra of mass versus intensity can be obtained for all elements virtually simultaneously. Quadrupoles are limited effectively to unit mass resolution so they can’t resolve polyatomic and isobaric interferences, Matrix dependent interferences should be thoroughly checked. However, of all of the elements detectable by ICPMS, only indium does not have an isotope that is free from overlap by another element. The ion signals are measured by the electron multiplier detector which operates in pulse mode for low and in analog mode for high concentrations samples.

Applications for the LA-Q-ICP-MS

Chemical composition

Trace elements and particularly rare earth elements in rock forming minerals like garnet, plagioclase, amphibole, pyroxene, olivine, leucite and in accessory phases like zircon and monazite can easily be determined in standard petrological thin-sections (normal size = 30 micron). Zircon grains are measured preferably embedded in epoxy resin, polished to expose their centers and already investigated for their internal structure via cathodoluminescence. The latter enables us to choose the optimal sector area for laser ablation.

Chemical zoning profiles

Garnet for example is an important mineral in metamorphic rocks which commonly shows a chemical zonation and contains inclusions of other minerals. Both zonation and inclusions provide valuable information about the metamorphic history of the garnet. Ablating a line across garnet yields a quick view of the element zonation and following specific single analyses provide exact element concentration

Whole rock REE and trace element concentrations from XRF beads

LA-Q-ICP-MS offers the feasibility to analyze the whole rock REE and trace element concentrations exact from the same fusion beads prepared for X-ray fluorescence (XRF) spectrometry analysis. In many cases, the REE content of a geological sample reflects the pristine composition of the rock formation and can, therefore, yield reliable information concerning magmatic processes and the reconstruction of palaeo-tectonic settings. Long-term measurements of the international geostandard BE-N demonstrate an external reproducibility for most of the REE which is <10%.

Determination of Au and PGE-Elements in sulfides

A synthetic pyrrhotite (Po724 B2 SRM, Memorial University of Newfoundland, Canada) doped with measured trace quantities of Au, Pt, Pd, Ru, Rh, Ir and Os enables the determination of these precious metals in sulfides. Furthermore our lab has the (Fe, Ni)1-xS sulfide standard, synthesized at the Universität of Münster for the determination of additionally Re and Ni. MASS-1 is used to analyze Ag, As, Cd, Co, Cr, Ga, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V, W, Cu, Zn, (Bi, In, Ir, Te, Tl).

Trace elements and REE-signature on columbite-tantalite („coltan“) ores

This project is a cooperation between the BGR (Hannover) and the University of Erlangen. After measuring the main elements using the electron microprobe, coltan concentrates were ablated in order to determine trace elements and REE contents of this conflict mineral. NIST 610 SRM glass was used for external calibration and Mn was used as internal standard element. There is a good agreement between the microprobe and Laser Ablation data for the trace elements. ID-results (Dr. Gäbler, BGR, pers. comm.) from a Fe-columbite are in good accordance with the Laser Ablation data.

Determination of REE and trace element concentrations for archaeological artefacts

LA-ICP-MS is an excellent technique to analyze quantitatively, almost non-destructively, archaeological objects (e.g. obsidian characterization, glass, glass-beads).

Qualitative analyses of steel, glass, fibrous and solid ceramics (AlN)

Performing numerous depth profile analyses yield insights of the element distribution in AlN-ceramics. The Figure below shows a REM-image with a cross section of a 100 micron wide and 140 micron deep laser crater in solid ceramic material with an ideal flat bottom (Klimera, Fraunhofer ISC). But also steel, glass and fibrous ceramics have been analyzed qualitatively.

lasercrater

REM-image with a cross section of a 100 micron wide and 140 micron deep laser crater in AlN-ceramics with a nearly ideal flat bottom.

Guests

The GeoZentrum Nordbayern offers interested scientists and material industries LA-Q-ICP-MS analyses. A custom-tailored analysis can be arranged upon request and all users are invited to be present during the analyses. Please contact us for details:

Prof. Dr. Reiner Klemd; reiner.klemd@fau.de, phone +49 (0)9131 85 22699

Dr. Helene Brätz; helene.braetz@fau.de, phone +49 (0)9131 85 22700