Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a powerful elemental and isotopic imaging technique based on a hyphenated setup of an ICP-MS instrument and a high-power laser used for sample introduction via laser ablation. The laser beam, impinged on the sample surface can remove material from the surface in the form of fine particles (an aerosol) through thermal and photon-dissociation processes (i.e. laser ablation). The aerosol is then transported to the plasma source of the ICP-MS instrument, which is capable of atomizing and ionizing the incoming particle stream. The positive excited ions are extracted into a mass analyzer of a mass spectrometer, after which a detector is used to characterize the position and/or time-of-arrival of individual ions into the detector.
Elemental image produced by HDIP. This is an image of lanthanide markers micro-villi of intestine tissue. Copyright Ghent University.
Advantages of LA-ICP-MS
-The default sample introduction device for ICP-MS is a pneumatic nebulizer and a spray chamber, hence, solid materials have to be taken into solution prior to analysis. The direct in-situ analysis of solid material using laser ablation can however be preferable if the sample of interest is very hard to dissolve, such that an elaborate sample pre-treatment, increasing the risk of analyte losses or contamination, is required. In general, no sample preparation is required.
- Solid sampling analysis is further characterized by a much higher sample throughput compared to liquid analysis. A characterization of the bulk contents of a solid material can be performed in a fraction of a second.
- Full dissolution of a sample, or large scrapings of material are not needed. Despite being a destructive technique, the sample damage is microscopic, and can be made so small that is no longer visible by the human eye. The typical sample mass of sample removed is in the femtogram to zeptogram range
- Improved absolute limits of detection. As the material that is introduced into the plasma is in a dry state, spectral interferences from hydroxides are heavily suppressed. In general, the dry plasma produces much cleaner/simpler spectra relative to solution ICP-MS. Compared to other elemental probes such as lab-scale XRF or LIBS, LA-ICP-MS is significantly more sensitive, with limits of detection in the ppb – parts per billion (and in some cases ppt) range.
- The mass spectrometers used typically have a very wide linear dynamic range, from 10E6 to 10E9. This means that trace elements and major elements can be quantified simultaneously.
- The mass spectrometer can monitor multiple elements. The information produced by LA-ICP-MS can cover a very large portion of the periodic table. Almost any element is accessible, with few exceptions (H, N, O, Ar and F). This also allows for trace element fingerprinting of solid samples, e.g. for provenance determination or forensic analysis.
- The ability of the laser to sample the material at a well-defined location – the diameter of the laser beam can be varied from < 1 µm to > 100 µm, while the penetration depth per shot is 10-500 nm allows for spatially resolved analysis of the sample surface. LA-ICP-MS can produce a 2- or 3-dimensional image of the elemental and isotopic distribution of the sample surface, as well as depth profiles. Local inclusions or sample defects can also be specifically targeted.
- A wide variety of samples can be analyzed, From conducting to non-conducting, inorganic to organic, almost any material is amendable to LA-ICP-MS. Even liquids are amendable in some cases. This is why the application field for the technique ranges from biology/medical/pharma, forensic, archaeology and geology to solid state. Furthermore, the analysis is performed under atmospheric pressures, so samples prone to outgassing are also amendable. Cryogenic options are also available.
- LA-ICP-MS can detect multiple nuclides of most elements at high precision, enabling isotopic analysis of materials. This has many applications, e.g. for geochronology.
- Laser ablation can be coupled to any type of ICP-MS. This can range from quadrupole-based systems, to sector-field MS, or even multi-collector ICP-MS, which is a dedicated tool for high-precision isotopic analysis.
This image shows a modern laser ablation system used for LA-ICP-MS. Image courtesy of Teledyne Photon Machines (http://www.teledynecetac.com/products/laser-ablation/iridia) .
Copyright @ LA-ICPMS.com, 2019