Trace element maps give unique insight to homogeneity, enrichment, and spatial distribution of elements in solid samples. Depending on the sample type, we can gain a wealth of information from sample maps beyond what is available from single or multiple spot analyses or single lines/rasters.
Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) provides high spatial lateral resolution and can be used to construct trace element maps with minimal destruction of the sample. A study using LA-ICP-MS completed by Teledyne CETAC, Arkansas Biosciences Institute and Arkansas State University compiled and interpreted elemental maps for three distinct sample types: banded iron formation (BIF), human teeth and fish otolith.
BIF in shale shows distinct hematite/quartz layers. Elemental maps of the BIF’s reflect the distinct matrix element layers and the trace element and REE distribution between the banded Si and Fe mineral phases. This type of information can be used to gain insight about the underlying bedrock composition, as well as the oxygenation and elemental composition of seawater at the time the rock was formed 3.4 Ga.
Human teeth were analyzed by LA-ICP-MS and cross-sectional maps were made to assess temporal variations in Pb and to monitor migration of heavy metals from dental amalgam into the teeth. Finally, fish otolith elemental abundances were mapped to explore spatial and temporal distribution of trace elements within and across annuli providing deeper insight into environmental life histories.
While other solid sampling methods such as SIMS, XRF, and EPMA may provide rival or comparable spatial resolution, LA-ICP-MS is a powerful tool for elucidating the spatial, quantitative distribution of trace elements. For this study, researchers used a CETAC LSX-213 Laser Ablation System and a PerkinElmer ELAN 9000 ICP-MS.
Samples
Researchers gather a sample of banded iron formation from the Eastern Indian Archean Craton of Singhbhum and Orissa. The BIF age was determined by U-Pb dating of zircon grains from a volcanic ash layer beneath the BIF layers. The age of the BIF is 3.4 billion years old making it the oldest and largest BIF deposit in the world. The tooth sample was a molar tooth extracted in 2008 from a 53-year old male, and the fish otolith sample was extracted from a 9-year old walleye from Devil;;s Fork on the Little Red River in Heber Springs, Arkansas.
Sample Prep
The samples were mounted on a petrographic slide and thin-sectioned using a Buehler IsoMet low speed saw with diamond wafering blades. Researchers used NIST SRM 2781, MACS-1 (USGS), and MAPS-1 (USGS) external calibration standards for calibration of the BIF, otolith, and teeth samples respectively. Laser Ablation and ICP-MS parameters were optimized to achieve stable signals for ubiquitous matrix elements while reducing oxides, doubly charged species and other potential interferences. For details on instrument parameters and images of the research study, download the Application Note from Teledyne CETAC.
Conclusion
Laser Ablation is an excellent sample introduction technique for generating spatially sensitive, high-resolution elemental maps for a variety of sample types. LA-ICP-MS elemental maps constructed using line scan methods make point-by-point calibration possible, providing a much faster means (compared to maps compiled from single spot analyses) for obtaining sensitive and reliable quantitative concentration data.
Download Application Note PST009 for additional details and testing results.
