FTIR-Photoacoustic spectroscopy of solids
Providing a way to rapidly analyze intractable samples, an Ames Laboratory device provides a wealth of chemical information that finds application for everything from characterizing hazardous wastes to answering industrial questions.
Based primarily on the use of a sensitive microphone, a Fourier Transform Infrared-Photoacoustic Spectroscopy (FTIR-PAS) device developed at Ames Laboratory eliminates the need for extensive sample preparation. FTIR-PAS also reduces analysis time, which translates into cost savings and faster processing of samples.
During operation, a modulated infrared beam from the FTIR spectrometer strikes the sample. The light is absorbed and produces heat that alters the pressure of the surrounding gas. The changing pressure is detected as sound by a microphone and is then converted to an absorption spectrum, which scientists read to identify and quantify the sample.
PAS found one potential application in the rapid characterization of waste tank sludges at the Department of Energy's Hanford, WA site, which has 177 underground storage tanks. Opaque and like peanut butter in consistency, these sludges required substantial sample preparation for conventional infrared spectroscopic analysis. With radioactive or chemically toxic sludge materials, this extra handling increases risks of worker exposure. With FTIR-PAS it is possible for workers to rapidly scan samples for radioactive and chemically active molecular species, such as nitrates, nitrites, sulfates and phosphates – all contaminants of concern. In addition, only milligram, versus gram-size samples are needed, reducing the exposure risks from hazardous samples.
PAS is also finding application in numerous industrial arenas. It has been used to produce a detailed chemical analysis (e.g., hemicellulose, glucan, lignin) from ground wood and it has been used to analyze sizings and coatings on paper, including qualitative depth profiling. Also, rapid, automated identification of polymers has been demonstrated at plastics recycling sites for both the computer and automobile industries.
During operation, a modulated infrared beam from the FTIR spectrometer strikes the sludge sample. The light is absorbed and produces heat that alters the pressure of the surrounding gas. The changing pressure is detected as sound by a microphone and is then converted to an absorption spectrum, which scientists read to identify and quantify the sample.
The FTIR-PAS is being used to analyze radioactive and chemically active molecular species, such as nitrates, nitrites, sulfates and phosphates; waste components of concern at the Department of Energy's Hanford, WA site, which has 177 underground storage tanks.
"The goal at Hanford is to provide a technique that would allow workers to rapidly scan these core samples, so they can determine what's there, even if it's just in a semi-quantitative way," says Bajic. "The FTIR-PAS system will help them know where to put the emphasis in a more complete analysis. Our technique should increase the efficiency of the characterization effort."
- Versatile Analytical Capabilities - The analytical capabilities of the FTIR-PAS can provide quick semi-quantitative results or more accurate quantitative results.
- Faster and More Efficient - Elimination of sample preparation steps cuts time required for individual analysis so that more samples can be analyzed in a given time period.
- Smaller Sample Size Required - As compared to gram-size samples required by other techniques, FTIR-PAS needs only a milligram-size sample to run an analysis, further reducing worker exposure to hazardous materials.
- More Cost-Effective - The FTIR-PAS saves money by reducing labor costs of time-consuming sample preparation.
- Safer Technique - Minimal sample preparation is required, reducing worker exposure to hazardous radioactive or toxic substances.
- Reduced Waste - No secondary waste is created during sample preparation or analysis.
The FTIR-Photoacoustic provides rapid and detailed chemical analysis using small, solid samples with a minimum of sample preparation. Thus the technique is faster, more cost-effective, and safer than many of its alternatives.
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