Fourier Transform Infrared Spectroscopy - Lab Report Example

Your Full Fourier Transform Infrared (FTIR) Spectroscopy Identification and quantification of unknowns can be carried out using the Fourier Transform Infrared (FTIR) Spectrometer. Functional groups give significant peaks at particular regions of the frequency range or wavenumber thus providing information on the chemical properties of different substances. Positional isomers of xylene were scanned and concentration of the unknown was linearly determined through the obtained peak responses. Introduction Fourier Transform Infrared (FTIR) is an analytical technique used primarily to identify compounds based on the responses of the functional groups present in its molecule. Different bonds in the molecule of these compounds give respective frequencies which are referred to as the wavenumber (Skoog 2007). As the technique developed, it is also now used for quantitative determinations. This experiment aims to provide knowledge in the use of FTIR in qualitative and quantitative applications. Quantitative determination of the xylene isomers is done through linear regression of the peak responses at the respective bands of the xylene isomers. Experimental In the experiment, a Perkin Elmer Spectrum One FT-IR Spectrometer was used. Qualitative analysis was done on the first part, and a quantitative test was conducted for the second part where the concentration of an unknown was determined using the known concentrations of m-xylene and p-xylene standards. Qualitative Determination. For the qualitative test, five different materials were scanned; namely polystyrene, polyethylene, polyacetate, cyclohexane and acetone. A background spectrum was first done on the FTIR spectrometer with range from 4000 – 500 cm-1, then the polystyrene was scanned once, then four scans, then sixteen scans. The effect of the number of scans was determined from this step. Five scans each of polyethylene and polyacetate films were done. The parameter was then changed to 4000 – 450 cm-1, then a NaCl liquid cell was placed in the steel frame. Background measurement was again conducted then the cell was filled with cyclohexane. The spectrum of cyclohexane was measured five times. The cell was then cleaned by pushing the liquid out using a syringe and collecting it on a paper towel. The cell was then rinsed with acetone and dried until there was no more detectable contaminant in the spectra. Acetone was then placed in the cell, and its spectra measured five times. Quantitative Determination. Solutions of m-xylene and p-xylene were prepared using cyclohexane as diluent at concentration levels ranging from 0 – 3% (v/v, volume of solute/volume of solution). These solutions had 2.0% (v/v) each of o-xylene which is the internal standard. The actual weight of m-xylene and p-xylene were recorded to make sure that the calculated concentrations are more accurate. The FTIR spectrometer was set at the range 850 – 600 cm-1 and five scans of each compound was done on absorption mode. The background spectrum was taken using the empty liquid NaCl cell. The corrected peak area and corrected peak height of each m-xylene and p-xylene solutions were recorded. The unknown was then scanned in the same manner and the corrected peak area and peak heights were also recorded. The values obtained were then used to plot the calibration curve and determine the amount of xylene isomer in the unknown. Results and Discussion Qualitative Analysis. The chemical structures of the reagents used for the analysis are presented in Table 1. Table 1. Chemical Structures of the Five Reagents for Qualitative Analysis (Britannica.com, n.d.). Chemical Structure Polystyrene Polyethylene Polyacetate Cyclohexane C6H12 Acetone CH3COCH3 The response of the functional groups in the FTIR can be clearly recognized based on the chemical structures of the reagents. The spectra and functional group identifications for the five reagents are presented in Appendix 1. Multiple scans generate more precise results than single scans because multiple scans is an average of single scans conducted in the sample over the period of the scan time (McMurry 2012). The amount of electromagnetic radiation absorbed by an organic compound causes a change in their electron state and this is the reason why molecular vibrations in bonds are observed. The molecular vibrations generated are unique for different functional groups. The chemical structure may now be deduced based on the presence or absence of the functional groups. However, identification of chemical structures will give more accurate results once a FTIR is used in tandem with other equipment like the GCMS or NMR (Skoog 2007). Quantitative Determination. The values obtained from the scans of p-xylene and m-xylene were plotted to be able to get the calibration curve. The plot was determined as the relationship between the area ratio for m-xylene or p-xylene with o-xylene and the concentration of the solutes expressed in % (v/v). Tables 2 and 3 presents the calculated area ratios for p-xylene and m-xylene. Spectra for the standard and unknown solutions are presented in Appendix 2. Table 2. Calculated area ratios for p-xylene. Conc, % (v/v) Area (p-xylene) Area (o-xylene) Area ratio 0.2629 0.80 7.56 0.10582 0.5198 1.53 7.87 0.19441 0.8125 0.55 7.95 0.06918 1.1735 1.94 7.76 0.25000 2.0729 1.01 7.85 0.12866 3.0857 6.58 7.65 0.86013 Table 3. Calculated area ratios for m-xylene. Conc, % (v/v) Area (m-xylene) Area (o-xylene) Area ratio 0.2237 4.26 6.84 0.62281 0.4660 1.06 7.55 0.14040 0.8060 0.99 7.48 0.13235 1.1832 2.71 7.02 0.38604 2.0172 4.14 6.72 0.61607 3.0780 6.79 5.76 1.17882 Using the data from the area ratios of m-xylene and p-xylene, a calibration curve was determined, as presented in Figure 1. It can be seen that the data obtained for both m-xylene and p-xylene are not linear, and that the calculated regression coefficients are 0.6429 for p-xylene and 0.6192 for m-xylene. The peak height ratio of p-xylene and m-xylene were also calculated to determine if there will be a linear relationship. The tables below presents the calculated peak height ratios for the two isomers against the internal standard, o-xylene. Figure 1. Calibration curves for m-xylene and p-xylene Based on Area Ratio Table 4. Calculated Peak Height Ratio for p-xylene. Conc, % (v/v) Height (p-xylene) Height (o-xylene) Height Ratio 0.2629 0.1156 1.6872 0.06852 0.5198 0.2485 1.8623 0.13344 0.8125 0.0756 1.9741 0.03830 1.1735 0.3212 1.8764 0.17118 2.0729 0.1611 1.8860 0.08542 3.0857 1.1055 1.8118 0.61017 Table 5. Calculated Peak Height Ratio for m-xylene. Conc, % (v/v) Height (m-xylene) Height (o-xylene) Height Ratio 0.2237 0.8261 1.7733 0.46585 0.4660 0.1987 1.8821 0.10557 0.8060 0.1806 1.8589 0.09715 1.1832 0.5311 1.7711 0.29987 2.0172 0.8036 1.6844 0.47708 3.0781 1.7670 1.1138 1.58646 Figure 2 is the graphical representation of the plot of peak height ratio and concentration for the m-xylene and p-xylene standard solutions. The linear correlation like that of the peak area ratio, are also not good. The regression coefficient for m-xylene is 0.6423, while that for p-xylene is 0.7018. This variation may greatly be due to the handling of the standards in the of m-xylene and p-xylene calibration solutions. The frequency range 850 – 600cm-1 is the only significant range since the positional isomers of xylenes will only exhibit a significant difference in the spectra within this region. An ortho disubtituted aromatic compound will show a strong and sharp peak between 735 to 770 cm-1, meta disubstituted aromatic compound peak will show a strong sharp peak between 750 – 810 cm-1 and 690 – 710cm-1, while the para substituted aromatic compound will show a strong and sharp absorption between 810-840 cm-1 frequency range (McMurry 2012). The o-xylene peak responses did not vary greatly, thus the non-linear curve obtained can be due to the actual amounts of the m-xylene and p-xylene present in the prepared solutions. Since these reagents are volatile, it is probable that some of the reagent has evaporated if it was not immediately diluted after weighing or that the containers were not properly covered to prevent volatilization of m-xylene and p-xylene. Figure 2. Calibration Curve for the Peak Height Ratio of m-xylene and p-xylene. Further, sampling techniques in the FTIR spectrometer may have also caused the discrepancy in the calibration curves, but this is nullified by the presence of the internal standard. The fact that there is not much variation in values of peak height and peak area of o-xylene, sampling technique can be ruled out as the possible source of error. The value obtained for the unknown will not be accurate because of the low regression coefficients for the standards, but still, the content of xylene isomers were still determined. Using the equation of the line, y = mx + b, the concentrations of the xylene isomers were calculated from the recorded peak responses, as presented in Table 6. Table 6. Determination of the Xylene Isomer Concentration o-xylene p-xylene m-xylene Area Height Area Height Area Height 7.38 1.7853 1.22 0.2165 0.28 0.0687 Peak Ratio 0.16576 0.12127 0.03804 0.03848 Calculated conc, % (v/v) 0.862 0.438 -0.328 0.410 Conc (mol/L) 0.070 0.035 -0.026 0.033 Sample Calculation For Peak area response of Unknown (p-xylene) Given: Equation of the line: y = 0.222x – 0.026 Area ratio for unknown (y): 0.16576 Slope (m) from calibration curve: 0.222 Y-intercept from calibration curve (b): -0.026 Calculate for concentration, in % (v/v), x From the equation of the line, y = mx + b, x = (y - b)/m, x = (y – b)/m = (0.16576 – (-0.026))/0.222 x = 0.862 %(v/v) Converting %(v/v), 0.862 %(v/v) / 100 * (1000mL/L) * (0.861 g/mL) / (106.16 g/mol) = 0.070 mol/L Conclusion Fourier Transform Infrared Spectroscopy is a useful tool in qualitative and quantitative determinations of different raw materials and other compounds. Innovations on sampling and handling techniques helped to improve the quality of results obtained using this kind of applications. The functional groups present in the compounds give specific intensities and wavenumbers which help in proper identification. FTIR can also be used for quantitative analysis by measuring the peak responses at specific wavenumbers of standard solutions and determining the concentration of the unknown through calibration curves. Sample and standard preparation should be consistent to be able to achieve reliable and accurate results. With standardized techniques, FTIR is a valuable tool in different chemical applications. Works Cited “Acetone”. Britannica. n.d. Web. Berry, M. Lung Cancer Screening by Breath Analysis. 1998. tobaccodocuments.org. Web. “Cyclohexane”. n.d. Britannica. Web. “Cyclohexane”. ChemicalBook. 2008. Web “FTIR Spectra of Polymers”. n.d. ftir-polymers.com. Web. McMurry, J. E. Organic Chemistry. 6th ed., Brooks/Cole, CA, 2012: Ch 12. Print. “Polyethylene”. Britannica. n.d. Web. “Polystyrene”. Britannica. n.d. Web. “Polyvinylacetate”. Britannica. n.d. Web. Skoog, D.A., F.J. Holler and S.R. Crouch. Principles of Instrumental Analysis, 6th ed., Thomson Brooks/Cole, CA, 2007: Ch 16 – 17. Print. Appendix 1 Spectra of Polystyrene and the Significant Peaks (ftir-polymers.com) Wavenumber (cm-1) Intensity Functional Group Bonds causing vibrations 3010-3100 medium Aromatic Ar C-H stretch 2850 - 2960 medium to strong alkanes C-H stretch 1450-1600 medium to strong aromatic Ring C=C stretch Spectra of Polyethylene and its Significant Peaks (ftir-polymer.com) Wavenumber (cm-1) Intensity Functional Group Bonds causing vibrations 2850 - 3000 strong alkanes C-H stretch 1370 - 1390 medium alkanes CH3C-H bend 715 - 725 weak alkanes -(CH2)n bend Spectra of Polyacetate and its Significant Peaks (ftir-polymers.com) Wavenumber (cm-1) Intensity Functional Group Bonds causing vibrations 1735 - 1750 strong esters C=O stretch ~1240 strong to very strong acetates O=C-O-C stretch 715 - 725 weak alkanes -(CH2)n bend Spectra of Cyclohexane and its Significant Peaks (chemicalbook.com) Wavenumber (cm-1) Intensity Functional Group Bonds causing vibrations 2850 - 3100 Medium to strong - sharp Aromatic Ring Ar C-H Stretch 500 - 1500 Weak to medium Fingerprint region Spectra of Acetone and its Significant Peaks (Berry 1998) Wavenumber (cm-1) Intensity Functional Group Bonds causing vibrations 1710-1720 Strong ketone C=O stretch 1370 - 1470 Medium to strong alkyl C-H bend Appendix 2 Spectra of 0.2% (v/v) p-xylene Spectra of 0.5% (v/v) p-xylene Spectra of 0.8% (v/v) p-xylene Spectra of 1.2% (v/v) p-xylene Spectra of 2.0% (v/v) p-xylene Spectra of 3.0% (v/v) p-xylene Spectra of 0.2% (v/v) m-xylene Spectra of 0.5% (v/v) m-xylene Spectra of 0.8% (v/v) m-xylene Spectra of 1.2% (v/v) m-xylene Spectra of 2.0% (v/v) m-xylene Spectra of 3.0% (v/v) m-xylene Spectra of the Unknown Read More