Thermo Scientific Nicolet iS10 Smart iTR (FTIR)
FTIR-ATR:
The Fourier transform infrared spectrometer available in KAUST-CU PTF is a mid-infrared (4000-400 cm-1 wavenumber) system with an ATR (attenuated total reflectance) Crystal. The mid-infrared range is used to study rotational-vibrational structure of molecules. The bond length and the molecules in the bond affect the frequency at which the bond will either rotate or vibrate and give a signature for the bond. The ATR allows for solid or liquid samples to be analyzed directly without any further preparation. This means you do not have to mix your sample with KBr. Be aware that the ATR technique interacts with only the surface of the material and for very thin films there may not be enough molecules on the surface to yield good results.
Important reminders:
The ATR crystal available in the KAUST-CU PTF FTIR is diamond. It allows for analysis of hard, reactive, caustic and corrosive materials. However, due to the molecular structure of a diamond there is intrinsic absorption from 2300 to 1800 cm-1. If you are interested in carbon-carbon chains or crystals, the diamond ATR is not an ideal choice for your sample.
As with all spectroscopy, cleanliness is very important and care should be taken to clean the sample lens before and after each sample as well as at the end of your run.
Software Interface:
The software that collects data from the SmartiTr is called Omnic. Once the software has started you will want to click the ‘Expt Set’ button or choose experiment setup from the ‘Collect’ Menu. First you will need to go to the ‘Bench Tab’, this is where you will determine the wavenumber range and the resolution you will use.
Above the peak graph choose ‘Peak to Peak’, this value should be between 2 and 7. There are 2 ways you can adjust the peak to peak value, you can adjust the resolution (this will cause a large change in the peak to peak value), or you can adjust the optical velocity (this will cause a small change in the peak to peak value).
Medium resolution is what is generally used and provides good data above the background, this also give you a data point every 0.486 cm-1 (At resolution of 4). If you require data points at closer intervals you will need to use high resolution. At high resolution you will have to use the lowest optical velocity for an acceptable peak to peak value. Changing the gain from 1, as gain is just amplifying data as it exists and not improving the quality or quantity.
Once the bench is set, then you can return to the collect tab. Here you can choose number of scans, resolution for the measurement (which must match the resolution set in the bench tab). Resolutions of 0.5-2 are high resolution, 4-12 are medium resolution and 16-32 are low resolution. When you select a resolution it will give you the data spacing and time for collection. You can choose final format for your data. You should choose to save the file automatically; you can choose a base name and should make it something easily recognizable to you.
Next you will set up the background handling. There are four choices, I recommend running a background before every sample or to use a background file. The number of scans for the background generally used is 16. If you choose to collect a background before each sample, save the experiment setup and choose ‘Col Sample’ it will prompt you to prepare a background, the software will measure the background and then prompt you to prepare your sample.
If you choose to use a background file save the experiment set up and close this window. Click the ‘Col Bkg’ button or select Collect Background from the collect menu. Run a background with a clean lens. When the background has finished, add to a new window and save the background. Once you’ve saved the background file, return to the experiment set up window and select the background file you just took. Select ‘Col Sample’ and it will prompt you to prepare your sample.
Sample Preparation:
The software will prompt you to prepare your sample in a popup screen; do not hit OK until you have placed your sample on the crystal. You should place your sample directly on the crystal, completely covering it, lower the sample clamp into place and tighten it. This is especially important for solid, powder or gel samples. The clamp is engineer to exert force onto your sample to place it into close contact with the crystal. You cannot over-tighten the clamp and damage the crystal. Once you’ve checked for crystal coverage and clamped your sample down you can then proceed to analyze your sample by clicking ok.
After data acquisition has taken place, you should add your data to a window, either an existing window or a new window. Once the data is in a window you can analyze the data, identify peaks or compare different spectra.
Functional Group / Molecular Motion / Wavenumber (cm-1)alkanes / C-H stretch / 2950-2800
CH2bend / ~1465
CH3bend / ~1375
CH2bend (4 or more) / ~720
alkenes / =CH stretch / 3100-3010
C=C stretch (isolated) / 1690-1630
C=C stretch (conjugated) / 1640-1610
C-H in-plane bend / 1430-1290
C-H bend (monosubstituted) / ~990 & ~910
C-H bend (disubstituted - E) / ~970
C-H bend (disubstituted - 1,1) / ~890
C-H bend (disubstituted - Z) / ~700
C-H bend (trisubstituted) / ~815
alkynes / acetylenic C-H stretch / ~3300
C,C triple bond stretch / ~2150
acetylenic C-H bend / 650-600
aromatics / C-H stretch / 3020-3000
C=C stretch / ~1600 & ~1475
C-H bend (mono) / 770-730 & 715-685
C-H bend (ortho) / 770-735
C-H bend (meta) / ~880 & ~780 & ~690
C-H bend (para) / 850-800
alcohols / O-H stretch / ~3650 or 3400-3300
C-O stretch / 1260-1000
ethers / C-O-C stretch (dialkyl) / 1300-1000
C-O-C stretch (diaryl) / ~1250 & ~1120
aldehydes / C-H aldehyde stretch / ~2850 & ~2750
C=O stretch / ~1725
ketones / C=O stretch / ~1715
C-C stretch / 1300-1100
carboxylic acids / O-H stretch / 3400-2400
C=O stretch / 1730-1700
C-O stretch / 1320-1210
O-H bend / 1440-1400
esters / C=O stretch / 1750-1735
C-C(O)-C stretch (acetates) / 1260-1230
C-C(O)-C stretch (all others) / 1210-1160
acid chlorides / C=O stretch / 1810-1775
C-Cl stretch / 730-550
anhydrides / C=O stretch / 1830-1800&1775-1740
C-O stretch / 1300-900
amines / N-H stretch (1 per N-H bond) / 3500-3300
N-H bend / 1640-1500
C-N Stretch (alkyl) / 1200-1025
C-N Stretch (aryl) / 1360-1250
N-H bend (oop) / ~800
amides / N-H stretch / 3500-3180
C=O stretch / 1680-1630
N-H bend / 1640-1550
N-H bend (1o) / 1570-1515
alkyl halides / C-F stretch / 1400-1000
C-Cl stretch / 785-540
C-Br stretch / 650-510
C-I stretch / 600-485
nitriles / C,N triple bond stretch / ~2250
isocyanates / -N=C=O stretch / ~2270
isothiocyanates / -N=C=S stretch / ~2125
imines / R2C=N-R stretch / 1690-1640
nitro groups / -NO2(aliphatic) / 1600-1530&1390-1300
-NO2(aromatic) / 1550-1490&1355-1315
mercaptans / S-H stretch / ~2550
sulfoxides / S=O stretch / ~1050
sulfones / S=O stretch / ~1300 & ~1150
sulfonates / S=O stretch / ~1350 & ~11750
S-O stretch / 1000-750
phosphines / P-H stretch / 2320-2270
PH bend / 1090-810
phosphine oxides / P=O / 1210-1140