Experiment 26 Quantitative Infrared Analysis of Isopropyl Alcohol in Toluene

Experiment 26 Quantitative Infrared Analysis of Isopropyl Alcohol in Toluene 

Discussion Isopropyl alcohol exhibits an infrared absorption peak at 817 cm-1. This peak is well isolated from any other peak due to either the analyte or toluene, the solvent. Thus, this peak is appropriate for quantitative analysis of isopropyl alcohol dissolved in toluene. Your instructor may ask you to disassemble and reassemble the cell so as to have the appropriate spacer in place. 

In dry 25-mL volumetric flasks, prepare four calibration standards of isopropyl alcohol in toluene solvent that are 20, 30, 40, and 50% in alcohol concentration. Obtain an unknown from your instructor and dilute to the mark with toluene. Shake well. 

Obtain a liquid sampling cell from your instructor and fill it with the 20% solution. Place this cell in the FTIR instrument, and obtain the transmittance spectrum according to the instructions specific to your instrument. Record the percent transmittance value at the tip of the 817 cm-1 peak and at the baseline. Repeat with the other three standards, the unknown, and the control sample. 

Convert all percent transmittance readings to absorbance. Subtract the absorbance at the baseline from the absorbance at the tip of the 817 cm 1 peak in each spectrum. 

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