Why is it important to be able to accommodate large samples on an FTIR microscope?

Significance of the topic

Non-destructive chemical analysis is essential when working with irreplaceable or sensitive samples (artworks, cultural heritage objects, geological specimens, etc.). FTIR microscopy enables molecular identification on small areas without altering the sample surface, but many important specimens are large, heavy, or require ancillary equipment that standard microscopes cannot accept. Adapting FTIR microscopes to accommodate oversized and heavy samples expands the range of real-world applications and preserves sample integrity during analysis.

Objectives and overview of the study

This application note demonstrates the analytical advantages of an FTIR microscope designed to handle large and heavy samples. Objectives include showing: the mechanical capability to accept thick/heavy specimens, the workflow for efficiently locating regions of interest on large surfaces, and the ability to identify minerals and degradation products non-destructively using mosaic imaging and spectral correlation.

Methodology and experimental approach

The approach combines wide-area visible mosaic imaging with targeted FTIR spectral mapping and library correlation. Large samples are placed on an open-access heavy-duty stage; the instrument collects a visible mosaic to rapidly survey the surface and creates infrared correlation images referenced to library spectra to locate specific chemical phases. Once a target area is found, the system acquires high-resolution infrared spectra or maps for definitive identification.

Used instrumentation

• Thermo Scientific Nicolet RaptIR FTIR Microscope with heavy-duty open-access stage (accommodates samples up to 40 mm thick and up to 5 kg).
• Infrared objectives (example: 15X IR objective) for localized spectroscopy.
• Support for large sampling accessories including heated/cooling stages, electrochemical cells, and inert-atmosphere cells.
• Visible camera and mosaic acquisition software for wide-area imaging and navigation, plus spectral library correlation tools for chemical mapping.

Main results and discussion

A 40 mm thick, irregular rock (563 g) was mounted and surveyed. A visible mosaic was acquired to locate regions of interest across the large sample. Infrared correlation imaging, using a lead carbonate (PbCO3) library spectrum, identified a localized area consistent with lead carbonate. This result was interpreted as a weathering product of galena (PbS); although PbS lacks a strong mid-IR signature, its weathering products (e.g., PbCO3) are infrared-active and serve as diagnostic markers. The workflow illustrated that: wide-area mosaics significantly reduce search time on large specimens, correlation images efficiently highlight chemically relevant areas, and subsequent high-resolution FTIR measurements confirm phase identification. The case also underscores the environmental and health relevance of identifying lead-bearing phases due to their toxicity and potential mobility.

Benefits and practical applications

• Non-destructive analysis of precious, archival, or hazardous specimens where sample alteration is unacceptable.
• Ability to analyze heavy or bulky samples (stones, coins, large paintings fragments, meteorites) and to integrate large accessories for controlled environments or electrochemical studies.
• Efficient workflow: wide-area mosaic imaging for rapid navigation, followed by high-resolution FTIR mapping at targeted locations.
• Enhanced environmental and safety assessment by identifying toxic weathering products (e.g., lead carbonates) without sample removal.

Future trends and possibilities of use

• Integration of automated AI-driven image and spectral analysis to prioritize areas of interest on very large mosaics and accelerate discovery.
• Expanded stage capacity and modular sample mounts to accommodate even larger cultural objects or multi-component assemblies.
• Closer coupling with complementary techniques (Raman microscopy, XRF, SEM) for multimodal, correlative analysis of complex materials.
• Improved in-situ environmental control (humidity, temperature, controlled atmospheres) for studying reactive weathering and conservation treatments on intact objects.
• Cloud-based acquisition and stitching workflows for remote collaboration and centralized spectral library updates tailored to heritage, geological, and industrial contexts.

Conclusion

Equipping FTIR microscopes with robust, open-access stages and efficient mosaic-based navigation transforms their applicability to large, valuable, or hazardous specimens. The demonstrated workflow—wide-area mosaics, infrared correlation imaging, and localized high-resolution spectroscopy—enables non-destructive identification of surface phases such as lead carbonates, improving conservation decision-making, environmental assessment, and scientific study of geological and cultural materials.

References

Thermo Fisher Scientific. Nicolet RaptIR FTIR Microscope application note/technical summary. 2022.