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Laser-ICP-MS

 

The GeoZentrum Nordbayern (Fachgruppe Krustendynamik) of the University Erlangen-Nürnberg obtained a Laser Ablation Unit (New Wave Research) coupled with a Agilent 7500i ICP-MS. The LA-ICP-MS is used for a variety of applications in earth sciences, material sciences and archaeological sciences

Laser ablation is the most versatile in-situ solid sampling technique for ICP-MS. The focussing characteristics of the laser allows investigations of small areas, local microanalysis and spatially resolved studies of nearly all materials are possible. 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, no matter if it is a lateral profile of a depth profil data aquisition.

Quantification of the signals occurs via standard reference material (e.g. NIST 610, NIST 612, NIST 614, Po724, (Fe, Ni)1-xS)). Repeated standard measurements were made throughout a measuring day for checking an eventually instrumental drift and they were measured again and again to determine the reproducibility and the accuracy of the results. The count rate obtained for a particular ion is compared to a calibration plot to yield the concentration for that element in the sample.

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Laser Ablation

A UP193Fx Argon Fluoride Fast eXcimer laser ablation system (New Wave Research, Fig.1) has been newly installed and coupled with the ICP-MS. This short pulse width (less than 4ns) laser system provides deep UV 193nm wavelength for excellent coupling and low depth penetration in all sample types, minimises fractionation and maximises irradiance (more than GW/cm2). Fully homogenised beam profile for super-flat craters, completely stable output energy and a finer particle distribution are some of the advantages of the UP193FX system. Ablation patterns can be varied (single spot, line of spots, line, raster etc.) as well as the final diameter of the laser beam (up to 150µm) 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.

Furthermore a New Wave frequency-quadrupled LUV266nm Nd:YAG laser system (Fig.2) capable of delivering an energy of 4 mJ to the sample site is available for Laser Ablation work which provides a means of rapid, direct analysis of solid samples without the need for lengthy chemical preparation and the benefit of minimal sample preparation.

 

Inductively 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 7500i has a triple-stage vacuum system with a rotary pump for the expansion region (interface) and two turbo-molecular pumps for the intermediate and analyser stages. The ion optic lens system can be adjusted manually to provide optimum ion transmission and high signal sensitivity. 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 milliseconds. 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. 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.

 

 

Kontakt

Prof. Dr. Reiner Klemd

Geozentrum Nordbayern
Fachgruppe Krustendynamik
Schlossgarten 5
91054 Erlangen

Tel: +49 09131 85 22699
undefinedklemd(at)geol.uni-erlangen(dot)de

 

Dr. Helene Brätz

Geozentrum Nordbayern
Fachgruppe Krustendynamik
Schlossgarten 5
91054 Erlangen

Tel: +49 09131 85 22700
undefinedbraetz(at)geol.uni-erlangen(dot)de

 

 

 

 

Fig.1: UP193FX Fast eXcimer laser ablation system

 

 

 

Fig. 2: Laser Ablation (LUV266x) - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS)