Instruments of NMR
- 1. Presented By : Name - Dnyanesh Mahesh Tayade Class - F.Y.M Pharm Department - Pharmaceutics JSPM’S Rajarshi Shahu College of Pharmacy And Research, Tathawade. 1
- 2. CONTENTS 1. NMR SPECTROMETER 2. INTRUMENTATION OF NMR 3. COMPONENTS OF NMR SPECTROMETER 4. REFERENCES 2
- 3. NMR SPECTROMETER • NMR Spectrometer is an instrument which is used to obtain NMR Spectra. • A high resolution spectrometer contains a complex collection of electronic equipments. • NMR spectrometers are referred to as 300 MHz instruments (or) 500 MHz instruments, depending upon the frequency of the RF radiation used for resonance. • These spectrometers use very powerful magnets to create a small but measurable energy difference between two possible spin states 3
- 4. Schematic presentation of a NMR 4
- 5. COMPONENTS OF NMR SPECTROMETER Magnet Field Lock Shim Coils Probe Unit - Sample Holder - RF Oscillator - Sweep Generator - RF Receiver Detector Read out Device 5
- 6. • The heart of both continuous-wave and Fourier form NMR instruments is the magnet. • Magnets produces the magnetic field, which determines the frequency of any nucleus. • Sensitivity and resolution are critically dependent on quality of magnet. • It should give homogenous magnetic field, i.e. the strength of the magnetic field should not change from point to point. • The magnet must be capable of producing a very strong magnetic field with strength at least 10,000 gauss Magnets 6
- 7. 1. Permanent Magnet: • Permanent magnets with field strengths of 0.7, 1.4, and 2.1 T are mostly used. • Permanent magnets are highly temperature-sensitive and require extensive thermostating and shielding as a consequence. • It is inexpensive and simple to operate. • They are operated up to 30 – 60 MHz • They provide field of good homogeneity. Disadvantage:- Field variation is not possible, as required, because different nuclei resonate at different magnetic field. Types of Magnets 7
- 8. 2. Electro Magnets: • They require power supply to produce magnetic field • Cooling system is required to counter the heat generated from the electric power. • They are more effective than the permanent magnet because of possibility of field variation • They are operated up to 60 - 90 MHz 8
- 9. 3. Super conducting magnet: • A super conducting magnet has an electromagnet made up of superconducting wire. • These magnets attain fields large as 21 T. • Superconducting wire has a resistance approximately equal to zero by immersing it in liquid helium (at 0° c). • Superconducting magnet systems be filled with liquid nitrogen every 10 days • The length of superconducting wire in the magnet is typically several miles. • They are operated up to 470 MHz Advantages : High field strengths, high stability, low operating cost, simplicity and small size compared with an electromagnet. 9
- 10. • In order to produce a high resolution NMR spectrum of a sample there is need of homogeneous magnetic field. • The field strength might vary due to aging of the magnet, movement of metal object near the magnet, and temperature fluctuations. FIELD LOCK 10
- 11. SHIM COILS • Shim coils are pairs of wire loops. • By using these coils Current is adjusted until the magnetic field has required homogeneity. • Magnetic field produced by the Shim coils cancels the small residual inhomogeneities in the magnetic field. • These inhomogeneities could be caused by the magnet design, materials in the probe, variations in the thickness of the sample tube. • Shimming must be carried out each time a new sample is introduced into the spectrometer. 11
- 12. PROBE UNIT • The sample probe is a device that holds the sample tube in a fixed position in the field and it is also provided with an air driven turbine for rotating the sample Tube along its longitudinal axis at several hundred RPM. • This rotation minimises the effects of inhomo- geneties in the field and as a consequence sharper lines and better resolution are obtained. 12
- 13. A.Sample holder: • Sample should be held in holder, which should be chemically inert, durable and transparent to RF radiation. • Glass tubes of about 8.5cm long and 0.3cm diameter are employed. • Glass tube are amberized in order to protect UV sensitive sample. • A spinner is provided to spin the tube at several rotations/min. in order to make the sample homogenous magnetic field. 13
- 14. B. Radiofrequency oscillator: • To irradiate the sample with electromagnetic radiation a highly stable crystal controlled oscillator coil is imposed right angle to the applied magnetic field. • To achieve maximum interaction of the RF radiation with the sample the oscillator coil is wound around the sample cell. 14
- 15. C. Sweep Generator : For a nucleus to resonate, the precession frequency should become equal to the frequency of the applied RF radiation. This can be achieved by 1. Frequency Sweep method: This method is used to resonate the nucleus. The frequency of the RF radiation is changed so that it become equal to resonance frequency or precession frequency. 2. Field sweep method: In this method, to resonate the nucleus the frequency of the RF radiation is kept constant and the precession frequency is changed by changing the applied magnetic field. 15
- 16. D. Radiofrequency receiver : • A few turns wire is wound around the sample tube tightly. • This receiver coil is perpendicular to both the external magnetic field and radio frequency oscillator. • When RF radiation is passed through the magnetized sample, the resonance occurs, which causes the current voltage across the coil to drop 16
- 17. DETECTOR • When radiation is passed through the sample, the two phenomena namely, absorption and dispersion may occur. • The observation of dispersion or absorption will enable the resonance frequency to be determined. There are two method to detect the resonance signals. A. Single coil method (Radiofrequency bridge method) B. Double coil method (Nuclear induction method) 17
- 18. • In this method coil used for surrounding the sample serves as both transmitter and receiver coil. • The applied signal is balanced against the received signal and the resonance signal is recorded as an out of balance e.m.f which may be amplified and recorded. A.Single coil method (Radiofrequency bridge) 18
- 19. B. Double coil method (Nuclear induction method) • In this method there are separate transmitter and receiver coils. • These two coils are fixed at right angle to each other as well to the direction of external magnetic field. • This energy transfer (induction) is influenced by magnetic nuclei in a sample placed between the two coils, as long as the RF current in the first coil was in resonance with nuclear transition. 19
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- 21. READ OUT DEVICE • The Absorption signal received from radio frequency receiver is extremely weak therefore it requires considerable amplification before it is fed to the chart recorder. • The received signal is amplified by the help of amplifier. And it is recorded by using a computer device. 21
- 22. REFERENCES 1. Chatwal GR, Anand SK. Spectroscopy. Himalaya publishing house; 2006 ; pg no. 2.203 – 2.206 2. YR Sharma. Elementary organic spectroscopy. S. & Company ltd; 2011; pg no. 189. 3. Principles of Instrumental Analysis - Doglas A Skoog, F. James Holler, Timothy A. Nieman, 5th edition, Eastern press, Bangalore, 1998; pg no. 470 - 473 4. Introduction to Spectroscopy, Donald L. Pavia, Gary M. Lampman, George S. Kriz, James A. Vyvyan, Cengage Learning, 2008. pg no. 114 – 116. 22
- 23. 23 THANK YOU