M2 REFLECTANCE INFRARED SPECTROSCOPY
Last Revised: August 2014 1. PURPOSE This exercise examines an alternative mechanism for recording the infrared spectra of “difficult” samples: attenuated total reflectance. 2. REAGENTS & EQUIPMENT 2.1 Varian FT‐IR spectrometer 2.2 ATR attachment 2.3 Piece of fabric 2.4 Samples of plastic, including translucent milk bottle container 2.5 Hand cream or similar moisturiser 2.6 Hair shampoo or liquid soaps – two (must be pH neutral) 2.7 Talcum powder 3. PROCEDURE All spectra (except the background) should be copied to a Word file. 3A. Normal transmission spectra 3.1 The instrument should be switched on 30 minutes before use. 3.2 Run a calibration and ensure that the “starburst” voltage is approximately 7‐8V. 3.3 Record an air background spectrum. 3.4 Record the transmission spectrum of the piece of “milk bottle” plastic. 3B. Using the ATR unit 3.5 Install the ATR unit as instructed. 3.6 Run a calibration and ensure that the “starburst” voltage is approximately 7‐8V. 3.7 Record an air background spectrum. 3.8 Place the piece of fabric on the plate, and record its spectrum. 3.9 Now clamp the fabric down as shown and record the spectrum. 3.10 Gently clamp the piece of “milk bottle” plastic onto the plate. Record out the spectrum. 3.11 Obtain three types of plastic, cutting out a small section if necessary to fit into the sample compartment. Record the spectrum of each. 3.12 One member of the group should wash and dry their hands thoroughly. 3.13 Record the spectrum of their skin, by placing the hand on the plate over the crystal as shown in the diagram. 3.14 Rub some hand lotion thoroughly into the area of the hand contacting the plate. Wipe off any excess, and run the spectrum again. 3.15 With your teacher’s assistance, subtract the before spectrum from the after. Display the three spectra on the one page before copying. 3.16 Clean the plate by wiping gently with tissue. plate
3.17 Install the liquid cup attachment. 3.18 Record the spectrum of:  talcum powder  the two shampoos/liquids soaps provided  water 4. REPORT Discussion 
describe and explain differences in the transmission and ATR spectra of the milk bottle plastic 
describe and explain differences in the spectra of the fabric piece, clamped and unclamped 
describe and explain differences in the “before and after” skin spectra 
comment on the use of the subtraction function for helping to make differences clearer 
examine the two shampoo/liquid soap spectra for differences that could help to distinguish them 
for each spectrum, identify any functional group peaks – tabulate these results 
identify the type of plastic in the milk bottle and the other samples by fingerprint region matching with the IR spectra books 
for each of the sample types examined, indicate whether their IR spectrum could recorded using transmission mode; if so, indicate the method; if not, explain why Questions 1.
How does the ATR technique work? 2.
What is the crystal used in the ATR attachment in our laboratory? Give TWO other alternative crystals. Compare the chemical and physical properties of the three. 3.
Why was it necessary to ensure that the pH of the shampoos/liquid soaps was between 5 & 9? 4.
How does diffuse reflectance differ from ATR? Which technique is simpler? Reference: Piketech application notes (see resource page) M2 p2