Laser Ablation ICP-MS Analysis at Oregon State University

General Information

Through the W.M. Keck Collaboratory for Plasma Spectrometry in the College of Oceanographic and Atmospheric Sciences (COAS) Oregon State University possesses world-class facilities for making Laser Ablation ICP-MS (LA-ICP-MS) measurements of a range of solid materials. These facilities may be used by internal or external users. The major users of the facility thus far are geologists and geochemists, interested in the chemical compositions of rocks, glasses and minerals, and fisheries biologists using otoliths to study fish life histories. However we have also used the equipment to study a wide range of other solid materials, including gels, plastics, alloys and more and would be happy to work with you to see if we can help you with your solids analysis needs.

Equipment

Since July 2011 we have been operating a Photon Machines G2 short pulse length ArF Excimer laser, equipped with two volume ablation cell. This laser is a substantial improvement over older facilities. The two volume cell can hold 9 x 1" round sample mounts or 3 x 1" round + 4 thin sections. The two volume cell also provides considerably better performance in terms of washout time, response, sensitivity and elemental fractionation. The larger sample cell also results in better sample throughput. There is also an improved range of spot sizes and shapes, including adjustable slits for sampling complex materials.

For mass analyzers we have a choice of two different ICP-MS systems:

Thermo Xseries2 quadrupole ICP-MS (web camera). Newly installed (July 2011) this instrument is dedicated almost exclusively to laser ablation. The combination of new laser and quadrupole system has lead to an improvement in sensitivty of 20-50 x for most trace elements Some of the common uses are:

• Analysis of lithophile trace elements (incl. Sc, V, Cr, Ni, Rb, Sr, Zr, Nb, Y, Ba, REE, Ta, Hf, Pb, U, Th etc.) in silicate minerals, melt inclusions and glasses.

• Measuring Sr/Ca ratios and trace element (Ba, Mg, Mn, Pb, Cu, Zn etc.) fish otoliths and scales.

• Elemental analysis of gels, plastics, alloys and other artificial materials

• Analysis of archeological materials

NuPlasma Multicollector ICP-MS. (WeB camera) This machine, installed in the Keck Collaboratory in mid 2003, is well suited to the measurement of isotope ratios via laser ablation. Using the new G2 laser system we are now routinely measuring Sr isotope signatures in otoliths and also working on Sr and Pb isotope techniques for geological materials.

Sample Preparation Guidelines:

Sample preparation requirements for Laser Ablation can be fairly minimal, and if required we can ablate non-polished surfaces and analyze vacuum-sensitive materials.  The only real limit is the size of object that can fit in the ablation chamber. However, for the best possible results it is often still best to conduct analyses on flat polished surfaces, which simplifies the interaction of the laser with the surface and makes it easier to document the exact location of each analysis point by reference to photomicrographs. Further, because LA-ICP-MS data is most commonly reduced by reference to an internal standard element that has an independently-known concentration (typically Si, Ca, Ti, Mg etc...), it may be best to prepare your sample so it can also be analyzed by electron microprobe in addition to laser ablation.

In general the sample chamber can fit two types of prepared sample materials:

1. Material mounted on American-size 2" x 1" (50 x 25 mm) petrographic thin sections. These should, if at all possible, be polished and above all should not have a cover slip. The overall thickness of material on top of the section can be up to ~1 mm. If you are preparing polished thin sections specifically for laser ablation analysis of rocks or other solids I would recommend making them ~ 100 microns thick to allow for extra ablation depth (although we can also analyze standard 30 micron thin sections if need be). Note that European-size 50 x 25 mm thin sections are slightly too large for the sample holder and need to be ground down (we can do this on site).

2. 25 mm diameter circular plugs similar to those commonly used for electron and ion microprobes. These can be up to ~15 mm thick. The mounting media can be any of the commonly used mounting materials - I generally use epoxy.

Sample Documentation

I cannot overstress the importance of good sample documentation. It is the solution to efficient use of machine time (less time spent finding out where you are on your sample = more time using the machine for analysis). The optics of the viewing system for the laser are good, but not great, and a good-quality photomosaic map of the sample surface taken in reflected light is your key to efficiently locating sample analysis points. For locations where point location is critical (e.g. small mineral inclusions or defects) a larger scale photo is also worthwhile. The laser optical system also has transmitted light, but not with crossed polarizers.

If you are visiting OSU to to laser ablation work you can bring the photos with you or use the facilities in the Department of Geosciences to make them after you arrive - but give yourself enough time to do this (at least an hour per sample map).

Fee Schedule

Fees for the use of the laser ablation system (for ExCell, Axiom or NuPlasma mass analyzers) are:

Academic user $60-80/hour

Commercial user $100/hour

Schedule analysis time

To discuss your analysis needs or schedule analysis time please contact: