IR Spectroscopy determination of xylene using an internal standard

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solutions: o-xylene, p-xylene, m-xylene, 3 concentrations of p-xylene tn cyclohex ane,3 concentrations of m-xylene in cyclohexane’ and 2 unknown 6k samples. We analyzed our samples using o-xylene as our standard to determine the concentrations of m-xylene and p-xylene in our unknown samples’ Standard curves were constructed from the ratio of absorbance of characteristic peaks. A trend line showingtheleast-Squarefithelpedtodeterminetheratioofconcentrationsinour unknown samPle. fM 7 wn’n-a‘”&7? Introduction a. ‘ Infrared spectroscopy is the spectroscopy that uses the infrared region of the electromagnetic spectrum, exciting molecules to higher vibrational states in order to detect energy of the vibrational modes in your sample’ It can be used a number ofways,oneofwhichisbasedonabsorptionspectroscopy. Isomers of organic molecules display a unique vibrational frequency; thus’ by ana|yzinga specific region of the spectrum, overlaying pure and different concentrations of a sample molecule as well as any backgrou na ‘p””t’fur’ it is , ,) , I /l possible to determine the concentration of an unknown sampl e’ 4 f{El,..l ‘ LLru Abstract We used a Fouri{er{ransform lnfrared spectro ^”$ ‘efto analyze 11 R, v A v”& L’az !{aks Wfl tr -ri o/’.’ t ,1 ,’S :/’ /) puryfuk-_’ * :- Experimental -,t.1:!o( _l/p’- t*- f,t. tr,”, tr, “t”u”‘ffi,, volumetric flasks, we made.kr samples of xylene and the different components of the mixture can be found below in the table’ Vol. unknown sample Vol. of cyclohexane (mL) Sample # Vol. of xylene (mL) o- Vol. of xylene (mL) p- Vol. of mxylene (mL) I 0.20 ) 0.20 0.20 3 1.88 4 0.10 0.02 1.85 5 0.10 0.05 0.10 1.80 6 0.10 0.02 1.88 7 0.10 0.05 1.85 8 0.10 1.80 9 0.10 0.10 0.10 1.80 10 0.10 0.10 1.80 L1 0.10 fable l. Preparation of the samples’ using the IRfspectrometer, a spectrum of an empty cell, in order to determine cell thickness, was taken as well as a sample of cyclohexane which was used as a reference. After which, spectrfi of the eleven samples prepared in the table tir/4,1 above were Performed” B , ? /* Results Figure 1 shows the overlaid spectra of the three isomers of xylene. The characteristic peak wavenumbers in the 650-750 cm-l regionwere found tobe742 cm-1 for o-xylene, J94 cmr for m-xylene and 690 and 769 cm-l for m-xylene. The absorbance values of the samples at these wavelengths were used to compute the A/Aoratio. As for m-xylene, we used the absorbance at 769 cm’t. Figure 2 and figure 3 show the spectra of samples 4-6 (the ones with p-xylene) and of samples 7-9 (with mxylene) respectively. i Spectra of pure xylenes i 2 1.8 1.6 1.4 0J ? 1.2 a! €1 o -H o.s 0.6 o.4 0.2 n 742 – o_xylene *” p_xylene – m_xylene 700 750 800 850 Wavenumber, cm-1 Figurel Spectra of of o-xylene, p-xylene and m-xylene in the 650-850 cm-l band Spectra of samples 4-5 o.25 o.23 0.21 0,19 dl 2 0.r7 (! € 0.1″s o 6 t 0.13 0.11 0.09 0.07 0.0s -sample 4 -sample 5 *53mpls g l Figure 2. Spectra of samples 4-6. 0.3 o.25 0.0s @ ? o.z t! ‘lt o -8 o.rs 0.1 -solution 7 . 5slutien g -solution 9 750 Wavenumber, cm-l Figure 3Spectra of samples 7-9. Spectra of samples 7-9 Spectra of unknowns o I c (! .cl o .ct 0.17 0.15 0.13 0.11 0.09 0.07 0.05 -‘–.unknown #1 .**unknsM6 ffl 6s0 750 850 Wavenumber, cm-l Figure 4 Spectra of the two unknowns’ Standard curves Standard curves were constructed from the data collected. The data is presented in tables II and III. Aoistheabsorbanceat742cm-l(fromo.xy|ene),Aistheabsorbance at794 cm-1 (signal from p-xylen el, C/Co is the ratio of the concentration of p-xylene over that of o-xylene. .Aoistheabsorbanceat.l42cm.1(fromo-xy|ene),Aistheabsorbance Sample # Lo 042 cm-l) L 094 cm’1) A/Ao ClCo 4 0.148 0.089 0.601 0.2 0.142 0.1 03 0.125 0.5 6 0.189 0.t61 0.884 1.0 Sample # Lo 042 cm-l) L ,769 cm-r) A/Ao ClCo 7 0.128 0.075 0.s86 0.2 8 0.207 0.104 0502 0.5 9 0.r17 0.118 0.662 1.0 at 769 cm-1 {signal from m-xylene), C/Co is the ratio of the concentration of m-xylene over that of o-xylene. p-xylene standard curve Y = 0.349 R2 L/Lo I Fig”t-St””A;rd “u-;for ftte”e. I m-xylene standard curve hl(9 0.7 0.65 0.6 o { o.ss 0.5 0.45 0.4 y = 0.124 R2= o.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 ClCo Jt- /u|j / (@) / tn>l;-! uututot( Ao (742 cm-1) N (794 cm’l) 0100 ArlAo ?_ Az (76e crr-1) AzlAo CrlCo C2lcd’ ) I 0.125 0.800 0.068 0″075 0.544 2.29 2.20 ) 0.r25 0.096 0.768 0.600 2.38 4.83 Table lV. Standard curve for m-xylene. J The quantitf C/Co fas calculated from the equation of the standard curves: Unknown 1: Ar/Ao = 0.3491(Crico) (c /co)=0800/0 s+gt – ry PWlff”1qp,’ @ I 2.29 Az/Ao- v/ v – {rffie] 6/.i’ —/ l 0.124r(Cz/Cd (CztCd – 0.544/0.124I U.J++|V.IL+ I – = 4.38 +.JO Unknown UIlliJlUWll nl Unknwn2 , Xl c. Y”l tY Ar/Ao -0.3491(CrlCo) I ,0 t (C1lC0) = 0.76810.3491 – 2.20 A2/As – 0.t241(czlCol (CzlCd = 0.600/0.r24r – 4.83 I From the values of C/Co we can caluflate the exact concentration of p-xylene and m-xylene in the samples, ifwe k ro*Vh” exact concentration of the stock solution of o-xylene used. Discussion The method of standard addition is quite straightforward and easy to carry on. Our standard curve for m-xylene, however, is not very reliable because the R2 value is too low. We think that the reason why it is so is that the three wavelengths )- selected do not correspond to the exact position of the peak, but approximate1t with an effor of about two wavenumbers. A way to solve this problem would be having more data points for the standard curve, since the signal-to- noise ratio increases linearly with the square root of the number of data points collected. q^ Conclusion The concentration of p-xylene and m-xylene in two unknown samples was determined through FTIR using the method of internal standards. fuS References 1. Skoog, Douglas A., F. James. Holler, and Stanley R. Crouch. Principles of re 4 Analysis. Belmont, CA: Thomson Brooks/Cole, 2007/W. trfl ‘,