Fourier Transform Infrared Spectroscopy (FTIR)

Objectives

The objectives of this experiment are:

1. Preparation of KBr Pellet

The first objective of this experiment is to prepare a potassium bromide (KBr) pellet containing an organic compound, exemplified by benzoic acid. This process involves meticulous sample preparation techniques to create a homogenous mixture of the organic compound and KBr. The preparation of the KBr pellet is essential for conducting Fourier Transform Infrared (FTIR) spectroscopy, as it allows for the analysis of the compound's infrared absorption characteristics.

2. Qualitative Analysis Using FTIR

The second objective is to perform a qualitative analysis of the organic compound, such as benzoic acid, utilizing FTIR spectroscopy.

FTIR is a powerful analytical technique that provides information about the functional groups present in a compound based on its infrared absorption spectrum. By subjecting the prepared KBr pellet to FTIR analysis, we can identify the characteristic absorption peaks corresponding to different functional groups within the organic compound.

3. Identification of IR Absorption Peaks and Functional Groups

The third objective is to identify the infrared (IR) absorption peaks and their corresponding functional groups in an unknown solid, liquid, or powder.

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By comparing the IR spectrum of the unknown sample to reference spectra or databases, we can deduce the functional groups present in the compound. This process allows for the characterization and identification of unknown organic compounds based on their spectral fingerprints, aiding in various fields such as chemistry, pharmaceuticals, and forensics.

Introduction

Fourier Transform Infrared (FTIR) spectroscopy stands as a cornerstone technique in modern analytical chemistry, offering unparalleled insights into the molecular composition of substances.

At its core, FTIR spectroscopy harnesses the principles of infrared light absorption to unveil the intricate molecular structures of compounds.

The essence of FTIR spectroscopy lies in its ability to measure the energy absorbed as infrared light traverses a monochromator. By directing the infrared radiation through an interferometer, the technique facilitates the acquisition of high-resolution spectra, capturing the nuanced interactions between molecules and electromagnetic radiation. This sophisticated methodological approach enables researchers to explore the vibrational modes of chemical bonds, unraveling the molecular intricacies with unprecedented precision.

Apparatus

• Die set
• Hydraulic press gauge
• Agate mortar and pestle
• Spatula
• Pellet holder
• Beaker

Materials

1. Potassium Bromide (KBr) - IR Grade

Potassium bromide, renowned for its exceptional transparency to infrared radiation, serves as a foundational component in FTIR spectroscopy. With its high purity and optical clarity, KBr facilitates the preparation of transparent pellets essential for sample analysis. The IR-grade KBr ensures minimal interference in spectral measurements, allowing researchers to obtain accurate and reliable results. Its versatility and compatibility with a wide range of organic and inorganic compounds make KBr an indispensable material in FTIR experiments, serving as the substrate upon which samples are analyzed.

2. Benzoic Acid

Benzoic acid, a ubiquitous organic compound, emerges as a focal point in FTIR analyses due to its distinct molecular structure and characteristic vibrational modes. As a model compound frequently employed in spectroscopic studies, benzoic acid offers valuable insights into the principles of infrared spectroscopy. By preparing KBr pellets infused with benzoic acid, researchers can elucidate the intricate vibrational signatures associated with its functional groups, such as the carboxylic acid moiety and aromatic ring. This compound serves as a reference standard, facilitating the calibration and validation of FTIR instruments while enabling qualitative and quantitative analyses of other substances.

3. Plastic

Plastic materials, encompassing a broad spectrum of synthetic polymers, feature prominently in FTIR investigations aimed at elucidating their molecular compositions and structural characteristics. From high-density polyethylene to polystyrene, plastics exhibit diverse infrared absorption spectra, reflecting the varied chemical compositions and bonding arrangements inherent to different polymer types. Through FTIR analysis, researchers can discern the unique vibrational modes associated with carbon-carbon and carbon-hydrogen bonds present in polymer chains, providing valuable insights into their molecular architectures and thermal properties. Plastic samples serve as invaluable subjects for FTIR studies, offering valuable insights into material science, polymer chemistry, and industrial applications.

4. Acetone

Acetone, a widely utilized solvent and organic compound, features prominently in FTIR spectroscopy owing to its distinctive infrared absorption spectrum. As a ketone compound, acetone exhibits characteristic absorption bands corresponding to the carbonyl functional group (C=O) and carbon-hydrogen (C-H) stretching vibrations. By subjecting acetone samples to FTIR analysis, researchers can identify and quantify its presence in various matrices, ranging from environmental samples to industrial solvents. Moreover, acetone serves as a valuable reference standard for calibrating FTIR instruments and validating analytical methodologies, ensuring the accuracy and reliability of spectral measurements.

5. Cyclohexane

Cyclohexane, a cycloalkane solvent widely employed in chemical synthesis and organic reactions, serves as a pivotal material in FTIR spectroscopy due to its characteristic infrared absorption spectrum. As a saturated hydrocarbon, cyclohexane exhibits distinct absorption bands corresponding to carbon-hydrogen (C-H) stretching vibrations, providing valuable insights into its molecular structure and conformational dynamics. By subjecting cyclohexane samples to FTIR analysis, researchers can elucidate its vibrational signatures and spectral features, enabling qualitative and quantitative assessments in diverse research fields, including organic chemistry, environmental science, and materials engineering.

6. Caffeine

Caffeine, a naturally occurring alkaloid found in coffee, tea, and various beverages, serves as an intriguing subject for FTIR spectroscopy due to its complex molecular structure and pharmacological significance. As a methylxanthine derivative, caffeine exhibits characteristic absorption bands corresponding to carbonyl (C=O), nitrogen-hydrogen (N-H), and carbon-carbon double bond (C=C) stretching vibrations, among others. By subjecting caffeine samples to FTIR analysis, researchers can discern its vibrational signatures and spectral features, facilitating qualitative identification and quantitative determination in pharmaceutical formulations, food products, and biological samples.

Procedure

Sample Preparation for IR Analysis

A. The KBr Method:

1. Sample Retrieval and Drying:
   • Obtain the solid sample, such as benzoic acid, and IR-grade KBr solid from the desiccator.
   • Weigh approximately 1 gram of each sample and place them in a drying oven at 110ºC for 2-3 hours to remove any moisture.
2. Grinding and Mixing:
   • Retrieve an agate mortar and pestle from the desiccator and ensure they are clean.
   • Transfer 1 mg of benzoic acid into the mortar and grind it until it becomes finely powdered and shiny, typically for about 1 minute.
   • Similarly, grind 80 mg of KBr powder in the mortar until it becomes a fine powder.
3. Homogeneous Mixture Preparation:
   • Combine the powdered benzoic acid and KBr in a ratio of 1:80 in the mortar.
   • Grind the mixture thoroughly for approximately 30 seconds to ensure homogeneity.
   • Scrape the mixture into the center of the mortar using a spatula and grind again for about 15 seconds to ensure thorough mixing.
4. Pellet Formation:
   • Heap the mixture in the center of the agate mortar.
   • Retrieve the die set and ensure it is clean.
   • Fill the die set's surface with the mixture.
   • Close the die set tightly and place it in the Hydraulic Press gauge.
   • Apply pressure gradually, increasing it to 7000 psi and then to 8500 psi.
   • Allow the pressurized mixture to rest for 2 minutes before releasing the pressure.
   • Slowly remove the die set from the Hydraulic Press gauge.
   • Open the die set and retrieve the KBr pellet, which should appear clear like a piece of glass or a transparent disk.
   • Place the KBr pellet into a pellet holder for further analysis.

Sample Preparation for FTIR (Reflectance)

Observations during Preparation of KBr Pellet:

• Ensure that the mixture of benzoic acid and powdered KBr is thoroughly homogeneous before pellet formation.
• If the mixture lacks homogeneity, it will not form a proper pellet, which could affect the accuracy and reliability of subsequent FTIR analysis results.

Conclusion

In summary, the experiment aimed to achieve three primary objectives: the preparation of a KBr pellet, qualitative analysis using FTIR, and identification of IR absorption peaks and functional groups in unknown substances.

Firstly, the preparation of the KBr pellet involved meticulous sample handling and mixing techniques to create a homogeneous mixture of the organic compound, exemplified by benzoic acid, and IR-grade KBr. This step is crucial as the resulting pellet serves as the substrate for FTIR analysis, allowing for the examination of the compound's infrared absorption characteristics.

Secondly, qualitative analysis using FTIR spectroscopy provided valuable insights into the molecular composition of the organic compound. By subjecting the prepared KBr pellet to FTIR analysis, characteristic absorption peaks corresponding to different functional groups within the compound were identified. This step facilitated the elucidation of the compound's molecular structure and provided a basis for further analysis.

Lastly, the identification of IR absorption peaks and functional groups in unknown substances enabled the characterization and classification of these compounds based on their spectral fingerprints. By comparing the IR spectrum of the unknown sample to reference spectra or databases, the functional groups present in the compound were deduced, aiding in its identification and characterization.

References

1. Bruker. O,. (2019, August 28). Attenuated Total Reflection (ATR) Mode - Advantages for FT-IR Spectroscopy. AZoM. Retrieved on October 19, 2019 from https://www.azom.com/article.aspx?ArticleID=5958.
2. Badrun. F. H., Muhammad. N. A. I & Ariffin. Z. (2013). Basic Instrumental Analysis Laboratory Experiments For An Introductory Course In Instrumental Analysis. Shah Alam, Selangor. UITM Press.
3. Rizal. T, (2016). Experiment 3: Fourier Transform Infrared. Retrieved from, https://www.prezi.com/ -f96_3pqwfl_/experiment-3-fourier-transformed-infrared/