NMR Mainpage
Preparing a Sample of Flax Seed Oil We have used NMR to measure the relative amounts of unsaturation in various fats and oils. Proton NMR is very convenient for measuring total unsaturation in these substances because protons attached to carbon-carbon double bonds are easily distinguished from other protons in the molecules. No special setup or calibration of the instrument is required. The “Organic Flax Seed Oil” dietary supplement shown here is typical of many similar preparations presently on the market.
Preparing an NMR Sample of an Encapsulated Oil These methods apply to the Anasazi EFT-60 (1.4 Tesla) instrument using 5 mm sample tubes. Step 1 – The tip of a glass Pasteur pipette is held against the surface of the soft gel. Gentle twisting and pushing punctures the gelatin capsule, allowing access to the oil.
Step 2 – Squeezing the capsule forces oil into the Pasteur pipette. The amount of oil shown in the pipette is adequate for proton NMR.
Step 3 – The tip of the Pasteur pipette is rapidly withdrawn and inserted into the NMR sample tube. The oil is allowed to drain into the tube.
Step 4 – The pipette used to deliver the oil is left in the NMR tube. CDCl3 (deuterochloroform) is added to the top of this pipette, rinsing the oil into the tube. The CDCl3 contains approximately 1% TMS (tetramethylsilane), as an internal standard. About 0.5 mL of CDCl3 is required. Immediately replace the cap on the CDCl3 bottle.
Step 5 – Cap the tube and tilt it back and forth to rinse the oil to the bottom. Wipe the tube clean with a tissue. If there is oil on the outside of the tube, rinse it thoroughly with acetone and wipe again. The sample tube is ready to be inserted in the spinner turbine. Cleanup: Pour your sample solution into the CDCl3 waste container. Replace the cap on the waste container! Clean out the tube by rinsing it 3-4 times with acetone.