ANALYSIS OF XYLENE MIXTURE BY INFRARED SPECTROSCOPY AS5 Last Revised: May 2015
1. REAGENTS & EQUIPMENT 1.1 Sandwich infrared cells S3 & S4 1.2 Cyclohexane/chloroform/hexane 1.3 Xylene isomers and mixture 2. PROCEDURE 2A. Spectra evaluation 2.1 Examine the provided spectra of the three xylene isomers to identify characteristic peaks which can be used for quantitative analysis. The peaks should be reasonably strong, separated from other peaks in the spectra. Isomer Characteristic Peak (cm‐1) 2.2
o‐ m‐ p‐ On the basis of your choice of peaks for the xylenes, examine the spectra of chloroform, hexane and cyclohexane to determine which is most suitable as a solvent. Solvent 2B. Standard preparation 2.3 Obtain a clean, dry 25 mL volumetric flask. 2.4 Weigh accurately about 0.75 g of o‐xylene, 2 g of m‐xylene and 1.5 g of p‐xylene into the flask. 2.5 Make up the mark with the chosen solvent. Label this flask STD3. 2.6 Pipette 5 mL of STD3 into a 10 mL volumetric flask and make up to the mark with solvent. Label this STD2. 2.7 Pipette 2 mL of STD3 into another 10 mL volumetric flask, fill with solvent and make up to the mark. Label this STD1. 2C. Sample preparation 2.8 Weigh accurately, in triplicate, about 1 g of commercial xylene mixture into a 10 mL volumetric flask. 2.9 The third sample is a recovery check: weigh accurately about 0.25 g of m‐xylene into the flask. 2.10 Make the flask up to the mark with solvent. 2D. Analysis 2.11 Clean cell S3 or S4 thoroughly by filling with solvent and blowing dry air through. 2.12 Record a background spectrum using the cell filled with solvent. 2.13 Record the spectrum of STD3, and with the aid of your teacher, locate and measure the absorbance of each of the characteristic xylene peaks. 2.14 Rinse the cell with solvent and the next solution. 2.15 Measure the absorbance of the peaks for the other standards and the two samples. REPORT Calculations Sample analysis 1.
Calculate the concentration of each isomer in the standards, in g/10 mL. 2.
Plot a calibration graph for each isomer of absorbance vs concentration. Determine the line‐of‐
best‐fit for each. 3.
Use this to determine the concentration of the three isomers in the samples, in g/10 mL. 4.
Calculate the %w/w of each isomer in each sample. 5.
Calculate the average % for each isomer. Recovery check 6.
Determine the concentration of m‐xylene in the RC, in g/10 mL (equal to the mass in the spiked sample, m1). 7.
Calculate the mass of m‐xylene in the RC sample, using the average % for m‐xylene determined from the samples (m2). 8.
Given that the mass of m‐xylene added to the RC is m3, calculate the % recovery as below.  m1  m2 
% re cov ery  100 x 
  m3 
Discussion 
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explain the reasons for the choice of the analyte peaks comment on the results obtained for: ○ the combined % of xylenes ○ the % recovery compare this method with another technique capable of analysing this mixture for each component Questions 1.
Name TWO industrial applications using xylenes. 2.
Describe one method by which xylene mixtures can be synthesised. AS5 p2 AS5. ANALYSIS OF XYLENE MIXTURE BY IR
RESULTS SHEET
Masses (g) o‐xylene m‐xylene (std) p‐xylene Sample 1 Sample 2 Recovery Check m‐xylene (RC) Absorbances Wavenumber => STD1 STD2 STD3 Sample 1 Sample 2 RC