Conducting Spectroscopy on Air-Sensitive Samples: Techniques and Best Practices

Spectroscopy is a powerful tool for probing the structural, electronic, and optical properties of various materials. However, certain samples—especially those prone to oxidation, hydrolysis, or other air-induced reactions—pose unique challenges.

Air-sensitive materials such as organometallic compounds, transition metal complexes, and reactive nanoparticles can rapidly degrade or change when exposed to oxygen or moisture, leading to inaccurate data or even hazardous reactions. Despite this, the need for specialized equipment and careful handling can make the process time-consuming and technically demanding.

Understanding Air-Sensitive Materials

Air-sensitive materials include a broad spectrum of compounds. Examples range from organometallic reagents like Grignard reagents and metal carbonyls to transition metal complexes containing low oxidation state metals such as Cr(II) or Fe(II). Even advanced materials like lead halide perovskites, critical to next-generation photovoltaics, are susceptible to air-induced degradation. Exposure to oxygen or moisture can lead to rapid changes in their chemical structure, often leaving the material unusable for further analysis. Many organic semiconductor materials also suffer from moisture or air sensitivity. However, with proper processing and encapsulation techniques, these materials can be extremely useful in many optoelectronic devices, such as OLEDs, photovoltaics, organic lasers and photodiodes. 

Essential Techniques for Air-Sensitive Spectroscopy

Several techniques can be employed to maintain the integrity of air-sensitive samples during spectroscopic measurements. Each method isolates the sample from exposure to oxygen and moisture, ensuring accurate and reproducible results.

Glove Box Spectroscopy

Conducting spectroscopy inside a glove box offers a controlled environment with a highly inert atmosphere suitable for air-sensitive materials. A glove box is filled with an inert gas, typically nitrogen or argon, and maintains oxygen and moisture levels below 1 part per million (ppm).

Glove box-based spectroscopy is best suited to smaller-scale experimental setups using a modular spectrometer. It is ideal for highly reactive materials such as lithium metal or certain metal-organic frameworks (MOFs), where even brief exposure to air can result in significant degradation.

Image Credit: Ossila Ltd 

Custom Spectroscopy Cells

Specialized cells designed for spectroscopy under inert conditions are another effective solution. These gas-tight cells feature valves that allow filling and sealing within a glove box or using a Schlenk line. They are equipped with windows made of spectrally transparent materials like sapphire or quartz, resistant to both the sample and solvents used.

The air-sensitive sample is added to the spectroscopy cells under an inert atmosphere before being sealed. The sample can then be transported to the spectrometer without being exposed to the ambient atmosphere to perform the measurements as usual. This method is best suited to larger-scale experiments in which the workspace of a glove box is not adequate.

Where is Air-Sensitive Spectroscopy Useful?

Air-sensitive spectroscopy is critical in fields ranging from organometallic chemistry to materials science to device engineering. For example, studying the optical properties of lead halide perovskites under inert conditions has enabled significant advancements in photovoltaic technology. Similarly, detailed spectroscopic analysis of reactive metal complexes has provided deeper insights into catalysis and material synthesis.

Image Credit: Ossila Ltd 

Best Practices for Success

To achieve accurate and reliable spectroscopic data when working with air-sensitive samples:

1. Minimize air exposure using a glove box or Schlenk line to handle and prepare samples. Avoid transferring samples through open air whenever possible.
2. Validate equipment to ensure that all instruments and sample holders are free of contaminants and capable of maintaining an inert environment.
3. Check for leaks by testing all seals and connections before starting measurements. Leaks can compromise the inert atmosphere and affect the sample integrity.
4. Choose appropriate materials when selecting spectroscopy cells and holders. Ensure they are made of materials compatible with the sample and solvent used, preventing unwanted reactions.

Conducting spectroscopy on air-sensitive samples requires meticulous preparation and specialized techniques. Glove box setups, Schlenk lines, and custom spectroscopy cells can protect materials from degradation, enabling accurate and insightful analysis. As the study of air-sensitive compounds continues to expand in catalysis, materials science, and renewable energy, mastering these techniques will be increasingly important for advancing scientific understanding and innovation.

This information has been sourced, reviewed and adapted from materials provided by Ossila Ltd.

For more information on this source, please visit Ossila Ltd.