BOWEN UNIVERSITY, IWO

COLLEGE OF AGRICULTURE, ENGINEERING AND SCIENCES

INDUSTRIAL CHEMISTRY PROGRAMME

COURSE CODE: CHM 313

COURSE TITLE: INSTRUMENTAL METHODS OF CHEMICAL ANALYSIS

SESSION: 2019/2020 ACADEMIC YEAR

SEMESTER: SECOND

CLASS MEETINGS: TIME RANGE DAY VENUE

10-11 am Monday New Chm. Gen. Lab

2-4 pm Tuesday Virtual teaching

LECTURER'S DETAILS:

NAME: DR. A.A. OLANREWAJU

MOBILE: +2348038078074

E-MAIL: adesoji.olanrewaju@bowen.edu.ng

ROOM/OFFICE NUMBER: CHEMISTRY BUILDING, 1ST FLOOR, RM 22

COURSE DESCRIPTION: CHM 313 2 CREDITS

Atomic and molecular emission and absorption techniques (AMEAS); gas and liquid

chromatography (GC/LC), high performance liquid chromatography (HPLC), mass spectrometer

(MS), inductive coupled plasma (ICP), ICP-MS, ICP-GC, X-ray, X-ray fluorescence, nuclear

magnetic resonance (NMR), electron spin resonance (ESR), refractometry, polarography,

voltammetry and calorimetry

MODULE 4

UNIT TITLE: Nuclear Magnetic Resonance (NMR) Spectroscopy

SUB-UNITS:

- Introduction

- Instrumentation

OBJECTIVES:

At the end of the lesson, students should be able to:

i) explain the meaning and basic concept of NMR spectroscopy

ii) describe the instrumental components of the NMR spectrometer

iii) explain the operation of NMR spectrometer

iv) draw the schematic diagram of NMR spectrometer

Introduction

Nuclear magnetic resonance (NMR) spectroscopy can be defined as a technique that is

based on quantization of the spin angular momentum of the nucleus. The technique is based on

the magnetic properties of certain atomic nuclei. Magnetic properties are only exhibited by

molecules that have either atoms with odd mass number or an uneven number of electrons.

Example of such nuclei are 1H, 13C, 15N, 19F and 31P with spin quantum number I = 1/2. The

nucleus of these atoms has both spin and magnetic properties. Nuclei are positively charged and

spin on an axis, thereby creating a magnetic moment or field, which is capable of interacting

with an externally applied field, either in an alignment (parallel orientation) or opposing (anti-

parallel orientation) form.

The basic phenomenon of NMR spectroscopy is similar to other forms of spectroscopy, such as

UV-visible spectroscopy. The absorption of an electromagnetic radio-frequency photon promotes

a nuclear spin from its ground state to its excited state. The generation of the ground and excited

NMR states requires the existence of an external magnetic field, and a very small population

difference between the two energy levels, compared to other forms of spectroscopy. The NMR

spectrometer are of different sizes depending on the strength of the applied magnetic field. In

NMR experiments, a solution of substance under investigation is placed in a strong magnetic

field and the solution is irradiated with radio frequency energy of appropriate frequencies. The

energy absorbed by the protons is recorded as NMR spectrum.

NMR Instrumentation

300 MHz NMR Spectrometer 400 MHz NMR Spectrometer

JEOL 400 MHz NMR SPECTROMETER IN DELHI UNIVERSITY LAB, INDIA

900 MHz NMR

The major elements of the basic components of an NMR spectrometer are:

magnet, console and host computer. The working function of an NMR spectrometer is

principally similar to a radio system, having components terms such as transmitter, synthesizer,

and receiver.

Schematic diagram of an NMR spectrometer

How it works?

The MAGNET produces a stable static magnetic field used to generate macroscopic

magnetization in an NMR sample. The transmitter induced the linear oscillating electromagnetic

field, B1 field, with a desirable strength to interact with nuclei under study. The NMR signal,

called the free induction decay (FID), generated in the probe coil after irradiation by radio

frequency (RF) pulses is first amplified by a preamplifier, then detected by a receiver. The

detected signal is digitized by an analog-to-digital converter (ADC) for data processing and

display on a host computer.

MAGNET

The accuracy and quality of the instrument depend on the strength of the magnet.

Resolution increases with increase in the field strength. There are three types of magnets that

can be used. These are:

(i) conventional magnet (30-60 MHz)

(ii) permanent or electromagnet (60-100 MHz)

(iii) super conducting solenoids (470-900 MHz)

There is a relationship between the external magnetic field, Bo and the frequency, υ;

This is known as Larmour equation:

υ = (γ/2п) Bo

where γ = gyromagnetic ratio = 267.53

Bo = magnetic field

υ = frequency

п = 22/7 or 3.142

Thus, in an applied field of 1.41 Tesla (14100 Gauss), the resonance or frequency is

approximately 60 MHz, whereas in an applied field of 2.35 T (23,500 G), the resonance or

frequency is 100 MHz.

There are many structures inside a magnet. Almost all high field NMR magnets are made

of superconducting (SC) solenoids, which are enclosed in a liquid helium vessel to achieve

superconductivity.

Liquid nitrogen is stored in a vessel outside the liquid helium vessel in order to minimize the loss

of the latter, since liquid nitrogen is about 40 times less expensive than liquid helium.

The use of high vacuum chamber is to prevent heat transfer between the vessels and the shell of

the magnet while radiation is prevented by the use of reflective shields made of aluminum foil

round the high vacuum

STRUCTURE INSIDE AN MMR MAGNET

STRUCTURE INSIDE AN MMR MAGNET

STRUCTURE INSIDE AN MMR MAGNET

TRANSMITTER

Transmitter provides RF pulses to irradiate the samples with a desired pulse length and

frequency at the correct phase and power level, likewise generating quadrature

transmitter is a pair of coils mounted perpendicular to the path of field and receiver coil

The transmitter channel consists of the following:

-Frequency synthesizer

-RF signal generator

-Transmitter controller

-RF amplifier

COMPONENTS OF AN NMR TRANSMITTER

Transmitter provides RF pulses to irradiate the samples with a desired pulse length and

frequency at the correct phase and power level, likewise generating quadrature

transmitter is a pair of coils mounted perpendicular to the path of field and receiver coil

The transmitter channel consists of the following:

COMPONENTS OF AN NMR TRANSMITTER

Transmitter provides RF pulses to irradiate the samples with a desired pulse length and

frequency at the correct phase and power level, likewise generating quadrature phase. The RF

transmitter is a pair of coils mounted perpendicular to the path of field and receiver coil

RECEIVER

A receiver is used to detect the NMR signal generated at the probe and amplify it to a

level suitable for digitization.

Detection is the process of demodulating the NMR signal from the carrier frequency, and

measures not only the amplitude or voltage of the signal but also the phase modulation. The very

weak RF signal from the probe is first amplified by a preamplifier to reduce the loss of signal

before it is transferred to the receiver inside the console.

The process of signal detection includes:

- preamplification

- several stages of RF signal amplification

- quadrature detection (separation of the NMR signal from the carrier frequency)

-amplification of the NMR (audio) signals.

Receivers with one mixing stage are called single conversion receivers while those with more

than one stage are multiple-conversion receivers

NMR SAMPLE PREPARATION AND TUBES

About 5-8 mg of the sample is dissolved in about 400 μL of deuterated solvents

tube for analysis.

NMR SAMPLE PREPARATION AND TUBES

8 mg of the sample is dissolved in about 400 μL of deuterated solvents

8 mg of the sample is dissolved in about 400 μL of deuterated solvents and put in NMR

Conclusion

The NMR spectrometer consists of various components which works together to convert

the radiofrequency radiation absorbs by the nuclei (majorly hydrogen atom) into NMR spectrum.

Assignment:

1. Discuss briefly on voltammetry?

References.

1. Harris, D.C. (2013). Exploring Chemical Analysis. Fifth edition, W.H. Freeman & Company,

New York, England

2. .Douglas, A.S., Donald, M.W., James, F.H. and Stanley, R.C. (2004). Fundamentals of

Analytical Chemistry, Eight Edition.

3. Frank Settle. Handbook of Instrumental Techniques for Analytical Chemistry.

4. Robert, M.S., Clayton, G.B., and Terence, C.M., (1974). Spectrometric Identification of

Organic Compounds. 3rd edition Wiley International.