nuclear magnetic resonance

NUCLEAR MAGNETIC RESONANCE

SPECTROSCOPYCHAIRMAN

Dr.T.PandiarajanProfessor

Food and agricultural process engineering

PRESENTED BYV.Siva Shankar1st Ph.D (agri process engg)2015 804 106

CONTENTS

• Introduction• NMR mechanism• Classification• Applications• Case Study• Conclusions• References

INTRODUCTION

• Nuclear magnetic resonance spectroscopy (NMR) was first developed in 1946.• Nuclear Magnetic Resonance (NMR) Spectroscopy is a non-destructive analytical

technique that is used to probe the nature and characteristics of molecular structure.• The NMR phenomenon is based on the fact that nuclei of atoms have magnetic

properties that can be utilized to yield chemical information.• Powerful analytical technique used to characterize organic molecules by identifying

carbon-hydrogen frameworks within molecules.

13C -NMR1H -NMR

NMR SPECTROSCOPY

• The source of energy in NMR is radio waves which have long wavelengths, and thus low energy and frequency.

• This waves can change the nuclear spins of some elements, including 1H and 13C.

• Frequency in the range of 300Mhz-500Mhz.

An NMR machine consists of:(1) A powerful, supercooled magnet (stable, with sensitive control, producing

a precise magnetic field). (2) A radio-frequency transmitter (emitting a very precise frequency). (3) A detector to measure the absorption of radiofrequency by the sample. (4) A recorder (to plot the output).

NMR TUBE

• An NMR tube is a thin glass walled tube.

• Typically NMR tubes come in 5 mm diameters but 10 mm and 3 mm samples are known.

MECHANISM OF NMR SPECTROSCOPY

• When a charged particle such as a proton spins on its axis, it creates a magnetic field. Thus, the nucleus can be considered to be a tiny bar magnet.

• Normally, these tiny bar magnets are randomly oriented in space. However, in the presence of a magnetic field B0, they are oriented with or against this applied field. More nuclei are oriented with the applied field because this arrangement is lower in energy.

Nuclei are shielded by the magnetic field produced by the surrounding electrons. The higher the electron density around the nucleus, the higher the magnetic field required to cause resonance.

CH3Cl Vs CH4lower electron higher electrondensity densityresonate at lower resonate at higherapplied field applied field

• The nuclei of some atoms spin: 1H, 13C, 19F, …

• The nuclei of many atoms do not spin: 2H, 12C, 16O, …

(moving charged particles generate a magnetic field ())

• When placed between the poles of a powerful magnet, spinning nuclei will align with or against the applied field creating an energy difference.

• Using a fixed radio frequency, the magnetic field is changed until the

ΔE = EEM.

• When the energies match, the nuclei can change spin states (resonate) and give off a magnetic signal.

When and Which nuclei will spin?

1H NMR—NUMBER OF SIGNALSThe number of NMR signals equals the number of different types of protons in a

compound.Protons in different environments give different NMR signals.Equivalent protons give the same NMR signal.

1H NMR—POSITION OF SIGNALSSince the electron experiences a lower magnetic field strength, it needs a lower frequency to achieve resonance. Lower frequency is to the right in an NMR spectrum, toward a lower chemical shift, so SHIELDING shifts the absorption upfield.

NMR Spectrum

Inte

nsity

10 9 8 7 6 5 4 3 2 1 0

chemical shift (ppm)

Magnetic field

1. Number of signals: How many different types of hydrogens in the molecule.

2. Position of signals (chemical shift): What types of hydrogens.

3. Relative areas under signals (integration): How many hydrogens of each type.

4. Splitting pattern: How many neighboring hydrogens.

INFORMATION FROM NMR SPECTRA

Position of signals (chemical shift): what types of hydrogens.

primary 0.9 ppmsecondary 1.3tertiary 1.5alcohols 1-5.5 H-O-allyl 1.7benzyl 2.2-3iodides 2-4 H-C-Ibromides 2.5-4 H-C-Brchlorides 3-4 H-C-Clalcohols 3.4-4 H-C-Oaromatic 6-8.5

toluene

ab

Integration (relative areas under each signal): how many hydrogens of each type.

a b cCH3CH2CH2Br a 3H a : b : c = 3 : 2 : 2

b 2Hc 2H

a b aCH3CHCH3 a 6H a : b = 6 : 1

Cl b 1H

Integration: measure the height of each “step” in the integration and then calculate the lowest whole number ratio: a:b:c = 24 mm : 16 mm : 32 mm = 1.5 : 1.0 : 2.0 3H : 2H : 4H

abc

If the formula is known ( C8H9OF ), add up all of the “steps” and divide by the number of hydrogens = (24 + 16 + 32 mm) / 9H = 8.0 mm / Hydrogen. a = 24 mm / 8.0 mm/H 3 H; b = 16 mm/8.0 mm/H 2H; c = 32 mm/8.0 mm/H 4H.

CARBOHYDRATE NMR SPECTROSCOPY

• Structure of monosaccharides and oligosaccharides.• Sugar conformations.• 500 MHz or greater.• 3 – 6 ppm. (13C NMR chemical shifts of carbohydrate ring carbons are 60 –

110 ppm).

APPLICATION OF NMR SPECTROSCOPY

Today, NMR has become a sophisticated and powerful analytical technology that has found a variety of applications in many disciplines of scientific research, medicine, and various industries.

Some of the applications of NMR spectroscopy are LISTED BELOW:

Solution structure Molecular dynamicsProtein folding Ionization stateProtein hydration

Energetic status of cells to monitor the fermentation of

yoghurts (using phosphorus 31 LR NMR)

Analysis of sample quality and process control

Cooking of various types of rice (proton NMR)

Examination of cell cultures in the mashing of beer (using proton NMR)

Applications

CASE STUDY

1. Absolute quantitative analysis for sorbic acid in processed foods using proton nuclear magnetic resonance spectroscopy.

2. Quantification of acesulfame potassium in processed foods by NMR

Tile:Absolute quantitative analysis for sorbic acid in processed foods using proton nuclear magnetic resonance spectroscopy.

Journal:Analytica Chimica Acta

Objective:1. Analysis of sorbic acid in processed foods.2. Comparison between NMR, HPLC and Neutralization titration (Sodium hydroxide) .

(Limit of SA is 0.13 g/kg)

Case Study 1

SAMPLE PREPARATION

Processed food Samples

Solvent extraction (NMR) and Steam Distillation (HPLC)

Extracted Sample

RESULTS AND DISCUSSION

(a) Cheese(b) Fish Paste(c) Sausage(d) Dried Cuttlefish

(e) Syrup (f) Jam

Comparison of SA contents between NMR and HPLC

CONCLUSION

• This analytical method using a combination of solvent extraction and NMR analysis was applied and validated to determine SA levels in processed foods and proved that the proposed method is useful for quantification of SA.

• Using HPLC took a more time for determination of SA content While, the proposed method takes less time for determination of SA content.

Tile:Quantification of acesulfame potassium in processed foods by NMR

Journal:Talanta

Objective:1. Analysis of Acesulfame potassium in processed foods.

Case Study 2

ACESULFAME POTASSIUM

• Acesulfame potassium(AceK) is a high-intensity, non-caloric artificial sweetener with a sweetening strength approximately 200 times that of sucrose.

• AceK is currently used in specific processed foods such as chewing gum, jam, ice cream, softdrink, and beverages

SAMPLE PREPARATION

Processed food Samples

Solvent extraction (NMR) and Dialysis (HPLC)

Extracted Sample

RESULTS

(a) Candy (b) Jelly 1(c) Jelly 2

(d) Biscuit (e) Soft drink

Comparison of proposed method and conventional methods for commercial processed foods

• In this study, the advantages of the proposed method has high accuracy as well as good linearity.

• And compared with the conventional method, the proposed method exhibited similar capabilities in the determination of AceK in various samples, but was significantly faster at 65min in comparison to 49h in the conventional method.

CONCLUSION

CONCLUSION• The NMR technique is non-destructive, non-invasive and applicable to a broad

range of systems: liquids and solids.• Advantage of NMR over HPLC and other conventional methods

• No pre-treatment is required.• Quick results• Less sample is enough• Very sensitive

• NMR given the great impetus for the development of new food products and food quality control.

REFERENCES

• Gadian, D.G. (1982) Nuclear Magnetic Resonance and its Application to Living Systems, Oxford Science Publications

• Sanders, J.K. and Hunter, B.K. (1987) Modern NMR Spectroscopy. A Guide for Chemists, Oxford University Press

• Wuthrich, K. (1986) NMR of Proteins and Nucleic Acids, Wiley• Lauterbur, P.C (1973) Nature 242,190-191• Guillou, C, Remaud, G. and Martin, G.J. (1991) Trends Food Sci. Technol. 2, 85-89• P. Petrakis, I. Touris, M. Liouni, M. Zervou, I. Kyrikou, R. Kokkinofta, C.R.

Theocharis, T.M. Mavromoustakos, J. Agric. Food Chem. 53 (2005) 5293–5303.• A. Caligiani, D. Acquotti, G. Palla, V. Bocchi, Anal. Chim. Acta 585 (2007) 110–119.

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