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Test your knowledge of FTIR and Raman spectroscopy with these 10 questions.
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A. Wavelength changes caused by molecular vibrations
B. Diffraction caused by Bragg’s law
C. Fluorescence caused by resonance energy transfer
D. Radiation caused by neutron scattering
1. Infrared (IR) spectroscopy measures a sample’s absorption of light. Which of the following does Raman spectroscopy measure?
In Raman spectroscopy, monochromatic light is used to irradiate a sample. Most of the light is absorbed or transmitted, but a small subset of the scattered light changes wavelength in response to molecular vibrations in the sample. This can be used as a molecular fingerprint to determine the chemical composition of a sample.
Answer: A. Wavelength changes caused by molecular vibrations
Source: Bruker (accessed 2021).
A. chiral, nonchiral
B. polar, nonpolar
C. organic, inorganic
D. colorless, pigmented
2. Near-infrared (NIR) spectroscopy can be used for sensing ____ compounds, while mid-infrared (mid-IR) spectroscopy is more useful for sensing ____ compounds.
Minerals, salts, and inorganic compounds tend not to absorb in the NIR region but do absorb in the mid-IR (MIR) spectrum.
Answer: C. organic, inorganic
Source: Chem Soc. Review, 2014.
A. Zinc selenide
B. Rock salt
3. Which of the following crystals is not typically used for attenuated total reflectance (ATR) spectroscopy?
ATR measures infrared absorption into and reflectance from the outer few microns of a sample placed on a crystal with a higher refractive index. Rock salt has a lower refractive index than the crystals used in ATR instruments, and it absorbs light at some mid-IR wavelengths.
Answer: B. Rock salt
Sources: Bruker 2021, Pike Technologies 2020, Phys. Rev. 1965.
A. To pasteurize milk and other products
B. To break lactose into its component monosaccharides
C. To monitor for microbial contaminants
D. To analyze the fat content of milk and cream
4. Why is IR spectroscopy used in dairy production?
Infrared spectroscopy is used both to quantify fatty acid content, by detecting absorption by carbonyl and carbon-hydrogen bonds, and to determine the size of fat globules based on how they scatter light. It’s used for quality control in the homogenization and production of cream, and whole and skim milk products.
Answer: D. To analyze fat content
Sources: J. Dairy Sci. 2012, Bruker 2021, J. Dairy Sci. 2006.
5. Adulteration of olive oil with other, cheaper oils is a common fraud. What is the lowest concentration of adulterant oil that can be detected using NIR spectroscopy?
When a known sample of pure extra-virgin olive oil was available to calibrate against, researchers at the University of Guelph were able to detect as little as 2.7% (w/w) adulterant oil. Without a sample to calibrate against, detection limits ranged from 10% to 20% depending on whether sunflower, corn, or another edible oil had been mixed in.
Answer: D. <5%
Sources: Botanical Adulterants Prevention Bulletin, Jan. 2020, Food Qual. Saf., 2018.
B. Polyvinyl chloride
6. Fourier transform infrared spectroscopy (FTIR) spectroscopy is often used to identify microplastics in environmental samples. Which of the following plastics is most abundant in ocean water and sea ice in the Ross Sea in Antarctica?
FTIR studies of surface water and sea ice off Antarctica showed that polypropylene, polyethylene, and polyamide were the most common pollutants.
Answer: A. Polypropylene
Sources: Chemosphere 2017, Mar. Pollut. Bull. 2020.
A. Improve radiation therapy
B. Find the margins of tumors while doing surgery
C. Determine which type of tissue a cancer originated in
D. Target chemotherapy to cancer cells
7. Cancer researchers hope to use spectroscopic biomarkers to do which of the following?
Researchers who developed a Raman spectroscopy system that can detect cancer cells in situ during brain surgery are working on developing it commercially.
Answer: B. Find the margins of a tumor during surgery
Sources: Cancer Metastasis Rev. 2018, Sci Rep 2018.
A. To determine how surface cracks formed
B. To find out what types of tools the artist used
C. To find out the age of a piece
D. To determine the thickness of underlying layers of paint
8. In the art history world, Raman spectroscopy is used to identify pigments and other materials, and for what other purpose?
A technique called spatially offset Raman spectroscopy lets researchers focus on spectra at specific depths below an opaque surface. Changes in the spectrum indicate where different paints were used. Spectroscopy can also be used to show “underdrawings,” the sketches that an artist made and then covered with paint.
Answer: D. The thickness of paint layers
Sources: Philos. Trans. R. Soc., A 2016.
A. Determining the species origin of a hair
B. Calculating the age of blood stains
C. Determining the age of a bone’s owner
D. Detecting illicit substances in fingerprints
9. IR spectroscopy is a powerful tool for forensic scientists. All but one of the following forensic analyses can be done using ATR-FTIR spectroscopy without destroying evidence. Which is the exception?
ATR-FTIR can be used to determine the age of bloodstains (with greater accuracy in older stains), detect explosives in fingerprints, and determine the origin of hairs and other fibers. Bone must be powdered before it can be analyzed using this method, so a sample must be destroyed.
Answer: C. Determining the age of a bone’s owner
Sources: App. Spectrosc. 2016, Sci Rep 2017, J. Forensic Sci. 2009, Vib. Spectrosc. 2018.
A. 1112 cm
B. 1609 cm
C. 1255 cm
D. 1958 cm
10. When using Raman spectroscopy to monitor epoxy resins as they cure, one peak of particular interest represents the epoxide ring. It is found at approximately what wave number?
Measuring curing is useful for manufacturing everything from boat hulls to wind turbines. While the strength of the epoxide peak diminishes over time, peaks at other wave numbers, representing the resin, remain constant.
Answer: C. 1255 cm
Sources: Composites Part A: Applied Science & Manufacturing 2013 DOI:10.1016/j.compositesa.2013.01.021.
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