Eximer Laser ICP-MS
Laser Ablation ICP-MS laboratory
The LA-ICPMS laboratory consists of an NWR 193 UC laser ablation system and an Agilent 7900 quadrupole mass spectrometer. The laboratory was optimized to provide exceptional performance for the analysis of fluid inclusions and silicate melt inclusions in minerals; however, it provides top performance for the analysis of a very broad range of materials. Other typical application areas include the in situ determination of trace and major element composition of minerals, U-Pb dating of zircons and other accessory minerals, trace element mapping, depth profiling, characterization of the composition of non-geologic materials from material, engineering and life sciences.
The laboratory is open to external users. For additional information, please contact Colin Bray (firstname.lastname@example.org).
Optics and visualization
- Exceptional image quality with a resolution of approximately 1 μm as the below image demonstrates. The diameter of the circle around the crosshair is 20 μm. The image was taken at 45% zoom level.
- The optical imaging is co-axial with the laser projection, therefore sub-surface features can accurately be targeted
- The depth of focus in small enough to allow estimation of the depth of sub-surface features, such as fluid and melt inclusions with ±5 μm precision.
Sensitivity and limits of detection
This instrument is solely used in laser ablation mode and much attention is paid to maintain very low gas blanks (0-4 cps on most heavy masses). This combined with the high sensitivities of the Agilent 7900 allows us to achieve sub ng/g detection limits for many elements even at routine analysis conditions. Please see the figures below and the supporting material for detailed information on sensitivities, gas blanks and detection limits.
The NWR 193 UC platform allows direct communication with the Agilent 7900, therefore fully automated data acquisition is possible from up to hundreds of pre-set analysis sites. The long-term reproducibility of the motorized stage is 4 μm. The washout time to background level is <5 s without, and <10 s with the signal smoothing device allowing for short wait time between the pre-set analyses.
The layer management tool in the NWR software allows importing scanned sample images, which can be linked to the sample position using two reference points, and subsequently used for orientation. The stage will move to any site selected by simply clicking on the scanned image. Similarly, sample images generated by other instrumentation (e.g. cathodoluminescence) can also be imported and used for orientation.
The size of the ablation cell is 100X100 mm, which allows simultaneous loading of 6 geologic size thin sections and several standard reference materials. The sensitivities are uniform over the entire ablation cell thanks to the two-volume design. Samples as tall as 2 cm can easily be accommodated in the ablation cell by lowering the adjustable bottom plate.
The highly effective flushing mechanism of the cell allows resuming work just 5 minutes after sample change.
Fluid and melt inclusion analysis
The instrument has been configured to provide excellent performance in fluid inclusion and silicate melt inclusion analysis. A custom made aperture wheel allows rapid stepwise beam opening commonly required for optimal fluid inclusion ablation. The short pulse-width excimer laser facilitates controlled ablation of quartz. The combination of the iris and XYR apertures allows for matching the size and shape of silicate melt inclusions. Any circular beam can be used between 1 and 150 μm diameter with single micron steps, while rectangular beams are available with independently variable X and Y dimensions between 1 and 110 μm and with any degree of rotation.
The short pulse-width excimer laser in combination with the robust plasma of the Agilent 7900 allows for fairly high level of matrix independence as demonstrated by the below figures. Therefore, for most common silicate minerals and glasses, the quantification of the LA-ICPMS analysis is possible using the total of the major element oxides as internal standard. Thus, no preliminary analysis of the investigated materials is required by an independent technique to obtain an internal standard. This also allows obtaining the bulk composition of materials with micro-scale heterogeneity (e.g. fine groundmass in volcanic rocks, symplectites) by using large beam diameter or line/raster analysis.