Determinationof Unknown Components of Contaminated Air Using Fourier TransformInfrared Spectroscopy (FTIR)



FourierTransform Infrared Spectroscopy is a biochemistry technique that isused for the analysis and identification of organic and inorganicchemical compounds. The technique has in recent past been used forthe identification of unknown chemical components in paints,polymers, pharmaceutical products, and other products including foodby use of FTIR instrument. The principal merit of this technique isthat it provides both quantitative as well as qualitative analysis oforganic and inorganic compounds (Skoog, Holler, and Crouch).

Thetechnique operates on the mechanism of the identification of chemicalbonds present in a molecule through infrared absorption spectrum. Thespectrum produced by FTIR is a profile of a sample, which reflects adistinctive molecular fingerprint for scanning compounds of differentcomponents. The FTIR instrument is capable of detecting functionalgroups and characterizes covalent bonds of the compounds underanalysis. The method has also been used for unknown identification ofcompounds and toxicity screening, organic and inorganic samplesanalysis and impurities screening among others. The techniquequantifies absorption of the infrared emission by samples againstwavelength of the samples. The infrared absorption bands aretypically used to identify molecular components and structure of thesample (ThermoNicolet).

Whensamples under analysis are subjected to infrared radiation, theyabsorb the radiations resulting in the excitation of the compound andas a result move to an upper vibrational state. The light wavelengthabsorbed, by the compound under test, releases energy when themolecule moves from the ground state to the excited state. Thiswavelength absorbed by the test particles represents the molecularstructure characteristics of the particle. The FTIR spectrometer iscomposed of an interferometer that modulates the wavelength producedfrom a source of broadband infrared. The instrument also has a sensorthat measures the strength of transmitted reproduced light as afunction of wavelength. The sensor generates a signal that is usuallyanalyzed using computerized Fourier transform to produce a singlebeam of spectrum presented as plots of intensity transmittance versuswavelength (Birkner and Qian).

Theidentification of an unknown compound is typically based on thecomparison of the unknown IR absorption range with the standardspectra of known material or from a computer database. Studiesconducted using FTIR techniques have shown that absorption bandsbetween 4000 and 1500 wavenumbers represent compound of functionalgroups that includes -OH, C=O, N-H, and CH3. Areas with wave numbersranging from 1500 to 400 are fingerprinting regions withintermolecular attractions and material specific.

Thisexperiment will involve the analysis of different compounds usingFTIR spectrometer and generation of their spectra. The compoundsinclude methyl iodine, ethylene, acetylene, the trans-DCE as well asa sample of the polluted air prepared in infrared cells. These willbe compared with predicted absorption spectra of this compound in thecomputer database. The main aim of this experiment is, therefore, toidentify the unknown components of the contaminated air sample usingFTIR spectroscopy. The other objectives include the identification ofthe pollutant that contaminated the air sample and calculation of thevariation of gas molecules using FTIR spectroscopy. The experimentalso aims at determining the roles played by FTIR spectrometry in thequantitative as well as qualitative analysis of chemicals.


Theanalysis was conducted using FTIR spectrometer. The FTIR spectrometer(Room 3480) was operated using OPUS 7.2 software found on thecomputer. Settings for scans, resolution, signal gain, IR data typewere set as per the software procedure before loading the samples foranalysis. Sample spectrum was run using single channels. Spectrumscollected included those for water, carbon dioxide, four referencesamples, and the unknown.Before analysis of the unknown airsample, the spectrometer automatically purged the cell cavity with N2to remove water and carbon dioxide.

Resultsand Discussion

Table1: Number of vibrations of molecules

TheTable 1 above indicates the vibrations of different gas moleculeswhen run through an FTIR spectrometer machine.

Figure1: Spectrum indicating dichloroethane gas analysis

Thefigure 1 above indicates wavenumbers of 3095 and fingerprints regionof 1656 to 821.

Figure2: Spectrum of Acetylene gas analysis

Thespectrum in figure 2 indicates acetylene gas analysis withwavenumbers of 3309 and fingerprinting regions of 1352 to 749.4

Figure3: Standard spectrum of ethylene gas cell

TheFigure 3 above indicates that wavenumbers of standard ethylene gas at3128 and fingerprinting wavenumbers of range 1913 to 896.25.

Figure4: Standard spectrum of methyl iodide gas cell

Thefigure 4 above indicates that methyl iodine gas has wavenumbers ofrange 2977 to 2975 and specificity of 1256 to 1057.

Figure5: Spectrum of unknown gas

Theunknown contaminated gas has wavenumbers 2976 to 2849 with specificwavenumbers being 1257 to 947.63. The readings indicate thatAcetylene may be a contaminant of this gas as its wavenumbers arewithin the range of standard acetylene values.

Figure6: Standard spectrum of acetylene gas cell

Thefigure above indicates that standard acetylene had wave numbers of3782 to 3423 indicating that the components of the compound hadfunctional groups -OH, C=O, N-H and CH3. The1596 to 1024 wave numbers are the standards for this gas.


Theresults indicate that the vibration of water, carbon dioxide, sulfurdioxide and dichloro difluoroethane were all determined (Table 1).These results show that vibration of SO3 was the highest at 1573followed by H2O2 at 1353. This is a clear indication that thewavenumber of dichlorofluoro ethane could be within 1353 to 1573.

Resultshave indicated that the contaminated air contained dichloroethane(Figure 2). The finding is in comparison to the standard spectra ofdichloroethane gas (Figure 7). The result is regarded as positivebecause the sample was obtained 20m away from an open strawberryfield of which on one side were cows feeding and the other, a naturalgas pumping place clearly indicating the possibility ofdichloroethane contamination. Results also indicate the presence ofacetylene gas in the contaminated air (Figure 3). This can beattributed to the fact that the sample was collected across the pathwhere a gas station having an auto repairs shop doing airconditioners repair as well as dry cleaning was operating. Sincethese activities are associated with acetylene gas production, thepresence of this gas in the contaminated air confirmed the pollution. The spectra of standard gasses indicate wavenumbers in thefingerprints region of 3000 to 821 (Figure 3 for ethylene, Figure 4for methyl iodide and Figure 6 for acetylene). These wavenumbers arewithin range as displayed by the spectra of contaminated gas, whichis 2976 to 947. The data provide a clear indication that all methyliodide, acetylene, and ethylene gasses are pollutants present in thecontaminated gas. The contaminated gas had a possibility of differentpollutants present. This is evidenced by the comparison of thestandard spectra and that of the contaminated gas (Figure 5). The sixsuspected chemicals thus include methyl iodide, acetylene, ethylene,carbon dioxide, and dichloroethane (Materials Evaluation andEngineering, Inc.).

Thequality of the results was good since all the spectra obtained forthe different chemicals were consistent with the others that had beenobtained from previous studies (Chemwiki, Lab 3). The spectra were,however, not exact as those in the computer databases and thestandard gas. The difference may have been brought about by errorsdue to sample contamination and the presence of impurities in thesample. Additional possible sources of error included the variationin wavelength that may have been due to the absorption of infraredradiation by different elements within the compound.


Thespectrum studied contained the chemicals ethylene and other gasseswhose spectra were observed to be similar to those of the standardgas ranges. The experiment was thus successful as all the aims, whichincluded determination of the spectra of different chemicals andidentification of pollutants present in the contaminated gas, wereachieved. Other objectives, which included determination of vibrationof various gas molecules, were equally realized. The contaminantspresent could have also originated from other sources, such as carbondioxide, which was present in the spectrometer. The experiment alsoprovided a platform for the understanding of the role of infraredlight in the quantification of compounds.

Itcan, therefore, be concluded that the operation was successful, andthe technique of FTIR spectroscopy utilized effectively in theidentification of unknown components of pollutants present in the airsample.


Birkner,N. Qian, W. Howan FTIR spectrometer operates.Chemwiki, N.p.n.d.

&quotLab3: FourierTransform Infrared Spectroscopy(FTIR).&quot Chemwiki. N.p., 02 Oct. 2013.

MaterialsEvaluation and Engineering, Inc. FourierTransform Infrared spectroscopy (FTIR).Materials Evaluation and Engineering, Inc., 2014, n.d.

Skoog,D. A. James, H. Stanley, R. C. Principlesof Instrumental Analysis.N.p.: n.p., n.d.

ThermoNicolet.Introductionto Fourier Transform Infrared Spectrometry. ThermoNicolet,N.p.,n.d.