PSCT 205 INST SCI AND TECH PROF. DIP II 2022 2023.pptx

COURSE TITLE: INSTRUMENTATION SCIENCE &
TECHNOLOGY I (PSCT 205)
 PROF. DIPLOMA II
 FIRST SEMESTER (SEMESTER THREE)
 2022/2023 ACADEMIC YEAR
 LECTURER: MR. YAW ODURO-OFORI

COURSE OBJECTIVES
 This Model adds further technical training
and competence to the knowledge and skill
acquire in the semester three (3).
 Students are expected to have practical
exposure to some instruments.

COURSE OUTLINE
 1. INSTRUMENTATION SELECTION, ERRORS AND CALIBRATION
 i) Use of Handbooks/types of instruments
 ii) Factors that influence instrument selection
 a) Accuracy: Point accuracy, percentage of full scale deflection,
 sample accuracy statement
 b) Precision or repeatability
 c) Resolution or discrimination
 d) sensitivity and Range
 e) Reliability and Cost environment
 f) High or Low ambient temperature
 g) Corrosive media, Nuclear radiation
 H) Explosive atmosphere
 I) Types of output

COURSE OUTLINE
 2. SOURCES OF ERROR
 i) Manufacturing errors
 ii) Design inadequacy
 iii) Operating errors
 iv) Environment errors
 v) Application errors
 vi) Mathematically theory of error

COURSE OUTLINE
3. TEMPERATURE MEASURING INSTRUMENTS
i) Temperature and standards
ii) Types of Thermometers
a) Expansion Thermometers
b) Chemical and Physical change methods
(Calorimeter/Calorimetry )
c) Errors in non-electrical thermometers
d) Temperature measurement by the thermometric effect
e) Radiation methods of temperature measurement
f) Calibration of thermometers and pyrometers


4. SOME SCIENTIFIC INSTRUMENTS
i) pH Meter and measurement
ii) Turbidity meter
iii) VIS and UV Spectrometry

i. TEMPERATURE AND STANDARDS
 There are three temperature scales in use today,
Fahrenheit, Celsius and Kelvin.
 Fahrenheit temperature scale is a scale based on
32 for the freezing point of water and 212 for the
boiling point of water, the interval between the
two being divided into 180 parts.

 Celsius scale, or centigrade scale: is a
temperature scale that is based on the
freezing point of water at 0°C and the boiling
point of water at 100°C.
 Fahrenheit scale: is a temperature scale that
is based on the freezing point of water at
32°F and the boiling point of water at 212°F.

ii. TYPES OF THERMOMETERS
Expansion thermometers are special thermometers
with which the temperature is determined by
measuring the different changes in length or volume
of two bodies as a result of a change in temperature.

Expansion thermometers can be divided into, depending on their
physical state
Liquid thermometer
Gas thermometer
Solid state thermometer

Liquid thermometers
consist of a small glass flask for receiving the thermometer
liquid with a fused calibrated glass capillary in front of a scale
.
In proportion to the change in temperature, the volume of the
liquid and the glass vessel change differently, which means
that the level in the capillary increases with increasing
temperature.

The temperature can be read from the level and the scale label.
Depending on the measuring range, different liquids are used, e.g.
B. ethanol (−120 ° C to 60 ° C), toluene (−90 ° C to 110 ° C) or n-
pentane (−200 ° C to 35 ° C) and earlier very often mercury (−35 ° C
up to 357 ° C), which nowadays can only be found in the scientific
field because it is still preferred because of its property of not
wetting glass.
The first usable mercury thermometers were built by Daniel G.
Fahrenheit . An alloy of gallium, indium and tin ( Galinstan ) has
established itself as a non-toxic substitute for mercury .

Minimum-maximum Thermometer
A special form of liquid thermometer is the minimum-
maximum thermometer . It consists of a U-shaped
glass capillary with two separate scales, one for the
maximum (rising from the bottom to the top), one for
the minimum temperature (falling from the bottom to
the top).
There are pistons at both ends of the capillary: at the
"minimum end" filled with alcohol, at the "maximum
end" evacuated or filled with alcohol vapor.

In the bend of the capillary there is mercury, which is pushed back
and forth by the expanding or contracting alcohol.
The alcohol serves as the actual temperature measuring liquid, the
mercury shows the temperature on both scales.
The temperature displayed on both scales should be the same,
otherwise the scales are not correctly positioned.

There are steel needles over both ends of the
mercury, which are shifted accordingly by the
mercury. There is a magnet on the back of the
thermometer that holds the needles in their
respective positions.
This enables the respective maximum and
minimum temperature since the thermometer was
last reset. The maximum / minimum display can
be reset by briefly removing the magnet (usually
with a reset button on the thermometer).

Liquid spring thermometers
Liquid spring thermometers consist of a vessel
to which a manometer is coupled via a capillary
tube . The vessel is filled with a liquid; mercury,
xylene, toluene or others are used. When the
temperature changes, the pressure in the
system rises or falls , which is indicated by the
pressure gauge. These thermometers can be
used between −60°C and 500°C.

Gas spring thermometers (or Gas thermometers)
Gas spring thermometers (or gas thermometers)
are constructed like liquid spring thermometers.
Instead of a liquid, they are filled with a gas
(nitrogen or helium at around 50 bar). The range of
application for these thermometers is from −200°C
to 800°C.

Solid-state thermometers
Solid-state thermometers are, for example, bimetal
strip thermometers in which two strips of different
metals are attached to one another.
Due to their different expansion coefficients, they
expand in different ways when the temperature
changes.
This causes the bimetal strip to bend. This is used
as a thermal switch in the iron, for example

TEMPERATURE MEASUREMENT BY CHEMICAL
AND PHYSICAL CHANGE METHODS
One technique we can use to measure the
amount of heat involved in a chemical or physical
process is known as calorimetry.
Calorimeter is used to measure amounts of heat
transferred to or from a substance.
To do so, the heat is exchanged with a calibrated
object (calorimeter).

The measurement of heat transfer using this approach
requires the definition of a system (the substance or
substances undergoing the chemical or physical change)
and its surroundings (the other components of the
measurement apparatus that serve to either provide heat
to the system or absorb heat from the system).
Knowledge of the heat capacity of the surroundings, and
careful measurements of the masses of the system and
surroundings and their temperatures before and after the
process allows one to calculate the heat transferred as
described in this section.

A calorimeter
A calorimeter is a device used to measure the
amount of heat involved in a chemical or physical
process.
For example, when an exothermic reaction occurs in
solution in a calorimeter, the heat produced by the
reaction is absorbed by the solution, which
increases its temperature.
When an endothermic reaction occurs, the heat
required is absorbed from the thermal energy of the
solution, which decreases its temperature.
The temperature change, along with the specific
heat and mass of the solution, can then be used to
calculate the amount of heat involved in either case.

Scientists use well-insulated calorimeters to prevent
the transfer of heat energy between the calorimeter
and its environment.
ASSIGNMENT: DRAW AND LABEL THE CALORIMETER
IN USE.
This enables the accurate determination of the heat
involved in chemical processes, the energy content of
foods, and so on.
These easy-to-use “coffee cup” calorimeters allow
more heat exchange with their surroundings, and

Commercial solution calorimeters are also available.
Relatively inexpensive calorimeters often consist of
two thin-walled cups that are nested in a way that
minimizes thermal contact during use,
along with an insulated cover, handheld stirrer, and
simple thermometer. More expensive calorimeters
used for industry and research typically have a well-
insulated, fully enclosed reaction vessel,
motorized stirring mechanism, and a more accurate
temperature sensor

Before we practice calorimetry problems involving chemical
reactions, consider a simpler example that illustrates the core
idea behind calorimetry. Suppose we initially have a high-
temperature substance, such as a hot piece of metal (M), and a
low-temperature substance, such as cool water (W).

If we place the metal in the water, heat will flow from M to
W.
The temperature of M will decrease, and the temperature of
W will increase, until the two substances have the same
temperature-that is, when they reach thermal equilibrium.
If this occurs in a calorimeter, ideally all of this heat transfer
occurs between the two substances, with no heat gained or
lost by either the calorimeter or the calorimeter’s
surroundings.
Under these ideal circumstances, the net heat change is

When we use calorimetry to determine the heat involved in a
chemical reaction, the same principles we have been
discussing apply.
The amount of heat absorbed by the calorimeter is often small
enough that we can neglect it (though not for highly accurate
measurements, as discussed later), and the calorimeter
minimizes energy exchange with the surroundings.
Because energy is neither created nor destroyed during a
chemical reaction, there is no overall energy change during the
reaction.

The heat produced or consumed in the reaction (the
“system”), q reaction, plus the heat absorbed or lost by
the solution (the “surroundings”), q solution, must add
up to zero:
This means that the amount of heat produced or
consumed in the reaction equals the amount of heat
absorbed or lost by the solution:
Qreaction = −qsolution

These calorimeters are used to measure the
metabolism of individuals under different
environmental conditions, different dietary regimes,
and with different health conditions, such as diabetes.
In humans, metabolism is typically measured in
Calories per day. A nutritional calorie (Calorie) is the
energy unit used to quantify the amount of energy
derived from the metabolism of foods; one Calorie is
equal to 1000 calories (1 kcal), the amount of energy
needed to heat 1 kg of water by 1°C.

Key Concepts and Summary
Calorimetry is used to measure the amount of thermal energy
transferred in a chemical or physical process.
This requires careful measurement of the temperature
change that occurs during the process and the masses of the
system and surroundings.

These measured quantities are then used to compute the
amount of heat produced or consumed in the process using
known mathematical relations.
Calorimeters are designed to minimize energy exchange
between the system being studied and its surroundings.
They range from simple coffee cup calorimeters used by
introductory chemistry students to sophisticated bomb
calorimeters used to determine the energy content of food.

How can a temperature change be measured in a chemical
reaction?
It uses devices called calorimeters, which measure the
change in temperature when a chemical reaction is carried
out. The magnitude of the temperature change depends on
the amount of heat released or absorbed and on the heat
capacity of the system.
Which instrument are used to measure the heat of the
reaction?

calorimeter
calorimeter, device for measuring the heat developed during a
mechanical, electrical, or chemical reaction, and for calculating
the heat capacity of materials.
What are the different types of temperature?
There are three temperature scales in use today, Fahrenheit,
Celsius and Kelvin.

ERRORS IN NON ELECTRICAL
THERMOMMETERS
What is the error of a thermometer: a relative
boundary error of a thermometer is expressed
as a percentage, e.g. δT = ±1%, an absolute
boundary error is expressed as a temperature
range,
e.g. ΔT = ±1°C.

Main Sources Of Errors Of Temperature Measurement:
It should be noted that the accuracy of temperature measurement
is dependent upon a number of factors. They are:
1. The instrument: The device itself will cause errors because of
in digital processing and physical issues (e.g. “cold junction
compensation” with thermo-couples).

2. Sensor: The sensor is often the greatest source of error
in the reading. It is also difficult to compensate for sensor
errors. It requires that only sensor ever be used with the
instrument and that it be used at a certain temperature.
Thermistors and PT100s are interchangeable 0.4°C.
Thermocouples, however, have much larger errors.
Type K can have errors up to 2.2°C and 1°C for Type T.

Main Sources Of Errors Of Temperature
Measurement:
Special tolerances can reduce the Type T’s errors by half and
make them acceptable for use with food. Type K should never
be used with food.
They are outside the 1°C accuracy required. Note that the
accuracy required is the total of the instrument and sensor
error.
For example, if an instrument has a 0.4°C error and a sensor
has a 0.8° error then they are not acceptable because the total
is 1.2°C error.

Many devices fail because they have an accuracy of
1° plus a percentage error of the reading (eg 1° +/-
3% of reading = 1.3°C at 10°C). It is the total possible
error that is important in determining if a system
complies with the standards.

3. Measurement error: This is difficult to predict and depends
upon the skill of the operator as well as what they are trying
to measure. Using the wrong device will produce a false reading.
For example an infra-red thermometer measures surface
temperature only. The temperature within the item could be
significantly different.

4. Difference between the assumed by the user,
the object effective emissivity (εa) and the true
object effective emissivity (are),
5. Difference between the assumed effective
background temperature Tba (a) and the true
value Tba (r),
6. Difference between the assumed effective
transmittance τa (a) and the true value τa (r),

Main Sources Of Errors Of Temperature
Measurement:
7. difference between the assumed optics
temperature Top(a) and the true value Top(r),
8. noise generated in detector or other analog
electronic blocks,
9. limited resolution of analogue/digital
converter,
10. limited accuracy of the black body used
during calibration.

TEMPERATURE MEASUREMENT BY THE
THERMO-ELECTRIC EFFECT:
The thermoelectric effect is the direct conversion
of temperature differences to electric voltage and
vice versa via a thermocouple.
Conversely, when a voltage is applied to it, heat is
transferred from one side to the other, creating a
temperature difference.

Thermoelectric Phenomena
Electrically conductive materials exhibit three types of
thermoelectric phenomena:
 the Seebeck effect,
 the Thompson effect, and
 the Peltier effect.
The use of thermocouples is based on thermoelectric phenomenon
discovered by Thomas Seebeck in 1821.
When any two metals are connected together, a voltage is developed
which is a function of the temperatures of the junctions and (mainly)
the difference in temperatures.

It was later found that the Seebeck voltage is the
sum of two effects: the Peltier effect, and the
Thompson effect.
The Peltier effect explains a voltage generated in
a junction of two metal wires.
The Thompson effect explains a voltage
generated by the temperature gradient in the
wires.

EMF Relationships for Thermocouples
Practical exploitation of the Seebeck effect to
measure temperature requires a combination of
two wires with dissimilar Seebeck coefficients.
The name thermocouple reflects the reality that
wires with two different compositions are
combined to form a thermocouple circuit.

Role of Junction in Temperature Measurement
Above equation shows how the EMF generated by a
thermocouple depends on the temperature difference
between the Tj and Tt.
All thermocouple circuits measure one temperature
relative to another.
The only way to obtain the absolute temperature of a
junction is to arrange the thermocouple circuit so that it
measures Tj relative to an independently known
temperature.
The known temperature is referred to as the reference
temperature Tr. A second thermocouple junction, called
the reference junction, is located in an environment at Tr.

How do you measure thermoelectric effect?
The thermoelectric potential is measured using a
high impedance voltmeter so that negligible
current passes across the contact resistances
and there will be negligible potential difference
between the sought component surface potential
and the electrode potential.

What is a thermoelectric device for measuring temperature?
Thermocouple, also called thermal junction, thermoelectric
thermometer, or thermel, a temperature-measuring device
consisting of two wires of different metals joined at each end.
One junction is placed where the temperature is to be measured,
and the other is kept at a constant lower temperature.

How do thermocouples measure temperature?
A thermocouple is a sensor that measures temperature.
It consists of two different types of metals, joined
together at one end. When the junction of the two
metals is heated or cooled, a voltage is created that can
be correlated back to the temperature.

What is the difference between thermometer and
thermocouple?
A thermometer is a device that measures temperature or a
temperature gradient (the degree of hotness or coldness of an
object). ... A thermocouple produces a temperature-dependent
voltage as a result of Seebeck effect, and this voltage can be
interpreted to measure temperature.

Is thermometer a temperature sensor?
A thermometer has two important elements: (1) a
temperature sensor (e.g. the bulb of a mercury-in-
glass thermometer or the pyrometric sensor in an
infrared thermometer) in which some change
occurs with a change in temperature; and (2) some
means of converting this change into a numerical
value (e.g. the visible scale.

CALIBRATION OF THERMOMETERS AND PYROMETERS
 What do pyrometers measure?
Pyrometer: A device for measuring relatively high
temperatures, such as are encountered in furnaces. Most
pyrometers work by measuring radiation from the body
whose temperature is to be measured.

How are pyrometers calibrated?
To calibrate an infrared pyrometer, the pyrometer
makes a measurement of the target plate.
The controlled temperature of the plate is
compared with the pyrometer reading.
The pyrometer is then adjusted until the difference
is minimal.
The high emissivity of the target plate minimizes
emissivity errors.

What is calibration of thermometer?
A thermometer is calibrated by measurements
at a series of temperature fixed points
(freezing/melting points,
 triple points or vapour pressure points of pure
materials).
 By using this method we insert the
thermometer in a fixed point cell which
provides the desired temperature point.

Working Principle of Pyrometer
The basic principle of the pyrometer is, it
measures the object's temperature by sensing the
heat/radiation emitted from the object without
making contact with the object.
It records the temperature level depending upon
the intensity of radiation emitted.

Which radiation is measured by pyrometer?
These are non-contact instruments for measuring
temperature, and as such their thermal mass is relatively
unimportant. They can be used for very high temperatures.
Radiation pyrometers focus the infrared radiation emitted by
the body onto a thermocouple contained within the
instrument.

What is the difference between thermometer and
pyrometer?
temperature gradient (the degree of hotness or coldness of an
object). A pyrometer is a type of remote-sensing thermometer used
to measure the temperature of distant objects. Various forms of
pyrometers have historically existed.

What is difference between thermocouple and
pyrometer?
Thermocouple is a transducer consisting of two
different metals welded together at each end; a
voltage is produced that is proportional to the
difference in temperature between the two
junctions (one of which is normally held at a known
temperature) while pyrometer is a thermometer
designed to measure.

Why is a thermocouple better than a thermometer?
temperature gradient (the degree of hotness or coldness
of an object). ... A thermocouple produces a temperature-
dependent voltage as a result of Seebeck effect, and this
voltage can be interpreted to measure temperature.

Is infrared a thermometer?
An infrared thermometer is a sensor that consists of a
lens to focus the infrared (IR) energy on to a detector,
which converts the energy to an electrical signal that
can be displayed in units of temperature after being
compensated for ambient temperature variation.

What are the types of pyrometer?
Pyrometers can be broadly classified into two categories - optical
pyrometers and infrared / radiation pyrometers. Optical
pyrometers – They are designed for measuring thermal radiation
in the visible spectrum. They measure the temperature of
extremely hot objects based on the color of the visible light they
emit

PH METER AND MEASUREMENT
 pH METER DESIGN AND WORKING
 A pH meter provides a value as to how acidic or alkaline a liquid is.
 The basic principle of the pH meter is to measure the concentration of
hydrogen ions. Acids dissolve in water forming positively charged hydrogen
ions (H+).
 The greater this concentration of hydrogen ions, the stronger the acid is.
Similarly alkali or bases dissolve in water forming negatively charged
hydrogen ions (OH-).

The stronger a base is the higher the concentration of
negatively charged hydrogen ions there are. The amount of
these hydrogen ions present solution is dissolved in some
amount of water determines the pH.
A pH value of 7 indicates a neutral solution. Pure water should
have a pH value of 7. Now pH values less than 7 indicate an
acidic solution while a pH value greater than 7 will indicate an
alkaline solution.
A solution with pH value of 1 is highly acidic and a solution of
pH value of 14 is highly alkaline.

A pH meter will be made up of a probe, which itself is made
up of two electrodes. This probe passes electrical signals to
a meter which displays the reading in pH units.
The glass probe has two electrodes because one is a glass
sensor electrode and the other is a reference electrode.
Some pH meters do have two separate probes in which case
one would be the sensor electrode and the other the reference
point.

Both electrodes are hollow bulbs containing a potassium
chloride solution with a silver chloride wire suspended into it.
The glass sensing electrode has a bulb made up of a very
special glass coated with silica and metal salts.
This glass sensing electrode measures the pH as the
concentration of hydrogen ions surrounding the tip of the
thin walled glass bulb.
 The reference electrode has a bulb made up of a non-
conductive glass or plastic.

 one metal is brought in contact with another, a
voltage difference occurs due to their differences
in electron mobility.
Similar is the case with two liquids. A pH meter
measures essentially the electro-chemical
potential between a known liquid inside the glass
electrode (membrane) and an unknown
liquid outside.

 Because the thin glass bulb allows mainly the agile and
small hydrogen ions to interact with the glass, the glass
electrode measures the electro-chemical potential of
hydrogen ions or the potential of hydrogen.
To complete the electrical circuit, also a reference
electrode is needed.

BASIC PRINCIPLE OF A pH METER GLASS BULB
A typical modern pH probe is a combination electrode, which
combines both the glass and reference electrodes into one
body.
The combination electrode consists of the following parts:
A sensing part of electrode, a bulb made from a specific glass Internal
electrode, usually silver chloride electrode or calomel electrode
Internal solution, usually a pH=7 buffered solution of 0.1 mol/L KCl for
pH electrodes.
Reference electrode, usually the same type as 2 Reference internal
solution, usually 0.1 mol/L KC Junction with studied solution, usually
made from ceramics or capillary with asbestos or quartz fiber.

Body of electrode, made from non-conductive glass or plastics.
The bottom of a pH electrode balloons out into a round thin
glass bulb.
The pH electrode is best thought of as a tube within a tube.
The innermost tube (the inner tube) contains an unchanging
1×10−7 mol/L HCl solution.
Also inside the inner tube is the cathode terminus of the
reference probe.

The anodic terminus wraps itself around the outside of
the inner tube and ends with the same sort of reference
probe as was on the inside of the inner tube.
It is filled with a reference solution of 0.1 mol/L KCl and
has contact with the solution on the outside of the Ph
probe by way of a porous plug that serves as a salt
bridge.

THE DESIGN OF pH PROBE
 A silver chloride electrode is a type of
reference electrode, commonly used in
electrochemical measurements.
For example, it is usually the internal reference
electrode in pH meters. The reaction is between the
silver metal (Ag) and its salt silver chloride (AgCl, also
called silver(I) chloride).
The corresponding equations can be presented as
follows:

This reaction is characterized by fast electrode kinetics,
meaning that a sufficiently high current can be passed
through the electrode with the 100% efficiency of the
redox reaction (dissolution of the metal or cathodic
deposition of the silver-ions).
The reaction has been proved to obey these equations in
solutions of pH values between 0 and 13.5.

 SILVER CHLORIDE ELECTRODE
The pH meter measures the potential difference and its
changes across the glass membrane.
The potential difference must be obtained between two points;
one is the electrode contacting the internal solution.
A second point is obtained by connecting to a reference
electrode, immersed in the studied solution.
Often, this reference electrode is built in the glass electrode
(a combination electrode), in a concentric double barrel body of
the device.

WORKING OF A pH METER
Ag/AgCl | HCl | glass || probed solution  reference
electrode)
AgCl(s) | KCl(aq) || 1×10-7M H+ solution || glass
membrane || Test Solution || KCl(aq) | AgCl(s) | Ag(s)
The potential difference relevant to pH
measurement builds up across the outside
glass/solution interface marked ||
The bulb is sealed to a thicker glass or plastic tube,
and filled, for example, with a solution of HCl (0.1
mol/dm3).

Preparation of Standard Buffer
Buffer Solution pH 4.00 (200°C) Transfer the content of buffer
capsule or tablet pH 4.00 into a 100 ml volumetric flask.
Dissolve in about 80 ml of purified water, make up the volume
to 100 ml with purified water & mix.
2. Buffer Solution pH 7.00 (200°C) Transfer the content of the
buffer capsule or tablet pH 7.00 into a 100 ml volumetric
flask. Dissolve in about 80 ml of purified water, make up
the
volume to 100 ml with purified water & mix.

3. Buffer Solution pH 9.20 (200C) Transfer the content of the
buffer capsule or tablet pH 9.2 into a 100 ml volumetric flask.
Dissolve in about 80 ml of purified water, make up the volume
to 100 ml with purified water & mix.

Calibration of pH meter:
 Operate the pH meter and electrode system according to the
manufacturer’s instructions or according to the applicable SOPS.
 All measurements should be made at the same temperature of
20°C to 25°C.
 The apparatus is calibrated with the buffer solution of potassium
hydrogen phthalate (primary standard) (buffer pH 4.0) and one
other buffer solution of different ph, preferably buffer pH 9.2.
 The measured pH of a third buffer pH 7.0 must not differ by more
than 0.05.

CALIBRATION PROCEDURE:
The instrument is calibrated to pH 4, 7 or 9.2 but
remembers to calibrate pH 7 first.
Dip the electrode in standard Buffer Solution of 7.00 pH
value. Measure the temperature of the solution and
place the temperature knob accordingly.
Bring the Function Switch of pH Mode.
Adjust the “Calibrate” control so that the display reads
7.00. Now again turn the Function Switch into Standby
Mode.

Remove the electrode from 7 pH buffer solution and wash
it with distilled water, soak & dry it.
Put the electrode in 4 pH buffer solutions.
Bring the Function Switch in pH Mode and Adjust the
“Slope %” (Right side of the instrument) so that the display
reads 4.00. Remove the electrode from 4 pH buffer solution
and wash it with distilled water.
Always keep the Function Switch at standby Mode after
measuring the pH value.

Precautions when measuring pH
1. Make sure that the meter is set to the pH Mode and
adjust the temperature to 25°C.
2. Place the electrode in the sample to be tested.
3. The pH of the solution appears in the display.
NOTE: Allow the display to stabilize before taking your reading!
4. Rinse the pH electrode and place it back in the storage solution.

edure and operation of pH Meter:
sure the temperature of the Liquid being examined to 20°C-25°C.
merse the glass electrode in the liquid to be examined.
n off the knobs to pH Checking & note.
en measuring the pH above 10, ensure that the electrode is
able for use under alkaline conditions & apply any correction
is necessary.
cord the pH of the solution used to standardize the meter and
ctrodes at the end of a set of measurements. If the difference
ween this reading and the original value is greater than 0.05,
set of measurements must be repeated.

Types of pH meters
 1. Traditional pH Meter
 2. Pen-like devices
 3. pH strips
 4. Holographic pH sensors
 5. Solid-state electrodes pH Meter
 6. Voltmeter display device

PSCT 205 INST SCI AND TECH PROF. DIP II 2022 2023.pptx

How would you calibrate a pH Meter with pH 7 and pH 2 Buffers in your analytical
Laboratory? List the steps in an orderly manner. (7marks)
ANS: Calibration of the Meters with pH 7 and pH 2 Buffers
i. Select the pH Mode and set the temperature control knob to 25°C.Adjust the cal 2 knob to read 100%.
ii. Rinse the electrode with deionized water and blot dry using a piece of tissue
iii. Place the electrode in the solution of pH 7 buffer, allowthe display to stabilize and, then, set the display to read
7 byadjusting cal 1. Remove the electrode from the buffer.
iv. Rinse the electrode with deionized water and blot dry using a piece of tissue
v. Place the electrode in the solution of pH 2 buffer, allowthe displayto stabilize and, then, set the display to read
vi. 2 by adjusting cal 2. Remove the electrode fromthe buffer.
vii. Rinse the electrode with deionized water and blot dry using a piece of tissue. (1mark * 7) (7marks)

ASSIGNMENT
 1. Draw the pH Meter designed and working
 2. Draw and label the pH probe

TURBIDIMETRY
INTRODUCTION
TURBIDITY
• Turbidity is the cloudiness or haziness of a fluid.
• The turbidity of a sample may be due to a single
chemical
substance or a combination of several.
TURBIDIMETER An instrument used to measure the
relative clarity of a fluid by measuring the amount of
light scattered by particles suspended in a fluid
sample.
A turbidimeter measures obstruction to determine the
haziness, or intensity of light, in a sample • Measured
in: nephelometric turbidity units (NTU).

What is the main difference of nephelometry
from turbidimetry?
In nephelometry the intensity of the scattered light is
measured, while, in turbidimetry, the intensity of light
transmitted through the sample is measured.
Nephelometric and turbidimetric measurements are used in
the determination of suspended material in natural waters
and in processing streams.

VIS UV SPECTROPHOTOMETER
 Introduction
 A. UV radiation and Electronic Excitations
 1. The difference in energy between molecular bonding, non-bonding and
anti-bonding orbitals ranges from 125-650 kJ/mole
 2. This energy corresponds to EM radiation in the ultraviolet (UV) region,
100-350 nm, and visible (VIS) regions 350-700 nm of the spectrum
 3. For comparison, recall the EM spectrum: g-rays X-rays UV IR Microwave
Radio
 4. Using IR we observed vibrational transitions with energies of 8-40
kJ/mol at wavelengths of 2500-15,000 nm 5.
 For purposes of our discussion, we will refer to UV and VIS spectroscopy
as UV Visible

Analysis When continuous wave radiation is passed
through a prism a diffraction pattern is produced (called
a spectrum) made up of all the wavelengths associated
with the incident radiation.
When continuous wave radiation passes through a
transparent material (solid or liquid) some of the
radiation might be absorbed by that material.

Radiation source Diffraction prism Spectrum with ‘gaps’
Transparent material that absorbs some radiation in it If, having
passed through the material, the beam is diffracted by passing
through a prism it will produce a light spectrum that has gaps in
it (caused by the absorption of radiation by the transparent
material through which is passed).
The effect of absorption of radiation on the transparent material
is to change is from a low energy state (called the ground state)
to a higher energy state (called the excited state).

The difference between all the spectroscopic techniques
is that they use different wavelength radiation that has
different associated energy which can cause different
modes of excitation in a molecule.
For instance, with infra red spectroscopy the low energy
radiation simply causes bonds to bend and stretch when
a molecule absorbs the radiation.
With high energy UV radiation the absorption of energy
causes transition of bonding electrons from a low energy
orbital to a higher energy orbital.
The energy of the ‘missing’ parts of the spectrum
corresponds exactly to the energy difference between the
orbitals involved inthe transition.

Energy transitions s* Unoccupied Energy p* n p s
Levels Occupied Energy Levels. The bonding
orbitals with which you are familiar are the
s-bonding orbitals typified by simple alkanes.
These are low energy (that is, stable). Next (in
terms of increasing energy) are the p-bonding
orbitals present in all functional groups that
contain double and triple bonds (e.g. carbonyl
groups and alkenes).

Higher energy still are the non-bonding orbitals present on
atoms that have lone pair(s) of electrons (oxygen, nitrogen,
sulfur and halogen containing compounds).
All of the above 3 kinds of orbitals may be occupied in the
ground state. Two other sort of orbitals, called antibonding
orbitals, can only be occupied by an electron in an excited
state (having absorbed UV for instance). These are the p*
and s* orbitals (the * denotes antibonding).

Although you are not too familiar with the concept of an
antibonding orbital just remember the following – whilst
electron density in a bonding orbital is a stabilising
influence it is a destabilising influence (bond weakening) in
an antibonding orbital.
Antibonding orbitals are unoccupied in the ground state
UV A transition of an electron from occupied to an
unoccupied energy level can be caused by UV radiation.
Not all transitions are allowed but the definition of which
are and which are not are beyond the scope of this tutorial.

For the time being be aware that commonly seen transitions are
p to p* which correctly implies that UV is useful with compounds
containing double bonds. A schematic of the transition of an
electron from p to p* is shown on the left.

The Spectroscopic Process
1. In UV spectroscopy, the sample is irradiated with the broad
spectrum of the UV radiation
2. If a particular electronic transition matches the energy
of a certain band of UV, it will be absorbed
3. The remaining UV light passes through the sample and
is observed
4. From this residual radiation a spectrum is obtained
with “gaps” at these discrete energies – this is called
an absorption spectrum.

 The Instrumentation
The instrumentation used to run a UV is shown below.
It involves two lamps (one for visible light and one for UV
light) and a series of mirrors and prisms as well as an
appropriate detector.
The spectrometer effectively varies the wavelength of the
light directed through a sample from high wavelength (low
energy) to low wavelength (high energy).
As it does so any chemical dissolved in a sample cell through
which the light is passing may undergo electroni transitions
from the ground state to the excited state when the incident
radiation energy is exactly the same as the energy difference
between these two states.

A recorder is then used to record, on a suitable
scale, the absorption of energy that occurs at
each of the wavelengths through which the
spectrometer scans.
The recorder assembly
The spectrometer itself – this houses the
lamps, mirrors, prisms and detector.
The spectrometer splits the beam of radiation into
two and passes one through a sample and one
through a reference solution (that is always made
up of the solvent in which you have dissolved the
sample).

The detector measures the difference between the sample
and reference readings and communicates this to the
recorder.
The samples are dissolved in a solvent which is transparent
to UV light and put into sample cells called cuvettes.
The cells themselves also have to be transparent to UV light
and are accurately made in all dimensions. They are
normally designed to allow the radiation to pass through the
sample over a distance of 1cm.

 Instrumentation
• Light source
– Deuterium and hydrogen lamps
– W filament lamp
– Xe arc lamps
• Sample containers
– Cuvettes (types of cuvettes)
• Plastic
• Glass
• Quartz

 Instrumentation
1. The construction of a traditional UV-VIS
spectrometer is very similar to an IR, as similar
functions – sample handling, irradiation,
detection and output are required
2. Here is a simple schematic that covers most
modern UV spectrometers:
Diagram: FOR UV-VIS INSTRUMENTATION

Instrumentation
3. Two sources are required to scan the entire UV-VIS band:
• Deuterium lamp – covers the UV – 200-330nm
• Tungsten lamp – covers 330-700nm
As with the dispersive IR, the lamps illuminate the entire band
of UV or visible light; the monochromator (grating or prism)
gradually changes the small bands of radiation sent to the
beam splitter
4. The beam splitter sends a separate band to a cell containing
the sample solution and a reference solution
5. The detector measures the difference between the
transmitted light through the sample (I) vs. the incident light
(I0) and sends his information to the recorder

Instrumentation
7. As with dispersive IR, time is required to cover the entire UV-
VIS band due to the mechanism of changing wavelengths
8. A recent improvement is the diode-array spectrophotometer –
here a prism (dispersion device) breaks apart the full
spectrum transmitted through the sample
9. Each individual band of UV is detected by a individual diodes
on a silicon wafer simultaneously – the obvious limitation is
the size of the diode, so some loss of resolution over
traditional instruments is observed sample Polychromator –
entrance slit and dispersion device UV-VIS sources Diode
array

Sample Handling
1. Virtually all UV spectra are recorded solution-phase
2. Cells can be made of plastic, glass or quartz
3. Only quartz is transparent in the full 200-700 nm
range; plastic and glass are only suitable for visible
spectra
4. Concentration (we will cover shortly) is empirically
determined A typical sample cell (commonly called a
cuvet):

Sample Handling
5. Solvents must be transparent in the region to be
observed; the wavelength where a solvent is no
longer transparent is referred to as the cutoff
6. Since spectra are only obtained up to 200nm
solvents typically only need to lack conjugated
p systems or carbonyls,

Common solvents and cutoff wavelength in nm:
1. Acetonitrile 190
2. Chloroform 240
3. Cyclohexane 195
4. 1,4-dioxane 215
5. 95% ethanol 205
6. n-hexane 201
7. Methanol 205
8. Iso-octane 195
9. Water 190

Sample Handling
7. Additionally solvents must preserve the fine
structure (where it is actually observed in UV!)
where possible
8. H-bonding further complicates the effect of
vibrational and rotational energy levels on
electronic transitions, dipole-dipole interacts less
so
9. The more non-polar the solvent, the better (this is
not always possible)

The Spectrum
1. The x-axis of the spectrum is in wavelength; 200-
350 nm for UV, 200-700nm for UV-VIS
determinations
2. Due to the lack of any fine structure, spectra are
rarely shown in their raw form, rather, the peak
maxima are simply reported as a numerical list
of “lamba max” values or lmax = 206 nm

The Spectrum
1. The y-axis of the spectrum is in absorbance, A
2. From the spectrometers point of view, absorbance is the inverse
of transmittance: A = log10 (I0/I)
3. From an experimental point of view, three other considerations
must be made:
i. a longer path length, l through the sample will cause more UV
light to be absorbed – linear effect
ii. the greater the concentration, c of the sample, the more UV
light will be absorbed – linear effect
iii. some electronic transitions are more effective at the
absorption of photon than others – molar absorptivity, ε this
may vary by orders of magnitude.

The Spectrum
4. These effects are combined into the Beer-Lambert
Law: A = ε.c.l
i. for most UV spectrometers, l would remain constant (standard
cells are typically 1 cm in path length)
ii. ii. concentration is typically varied depending on the strength of
absorption observed or expected –typically dilute – sub . 001 M I
iii. molar absorptivities vary by orders of magnitude:
• values of 104-106 are termed high intensity absorptions
• values of 103-104 are termed low intensity absorptions
• values of 0 to 103 are the absorptions of forbidden transitions A
is unitless, so the units for e are cm-1 · M-1 and are rarely
expressed

5. Since path length and concentration effects can
be easily factored out, absorbance simply
becomes proportional to e, and the y-axis is
expressed as e directly or as the logarithm of ε

Practical application of UV spectroscopy
1. UV was the first organic spectral method, however, it is
rarely used as a primary method for structure determination
2. It is most useful in combination with NMR and IR data to
elucidate unique electronic features that may be ambiguous in
those methods
3. It can be used to assay for photochemical experiments,
or the design of UV resistant paints and coatings
4. The most ubiquitous use of UV is as a detection device for HPLC;
since UV is utilized for solution phase samples vs. a reference
solvent this is easily incorporated into LC design.

Visible Spectroscopy (VIS)
• The portion of the EM spectrum from 400-800 is observable
to humans- we (and some other mammals) have the
adaptation of seeing color at the expense of greater detail,
400 - 500 - 600 - 700 - 800
wave length/nm
Violet 400-420
Indigo 420-440
Blue 440-490 Green 490-570
Yellow 570-585 Orange 585-620
Red 620-780

Visible Spectroscopy
• When white (continuum of l) light passes through, or is
reflected by a surface, those ls that are absorbed are
removed from the transmitted or reflected light
respectively
• What is “seen” is the complimentary colors (those that
are not absorbed)
• This is the origin of the “color wheel”

• Organic compounds that are “colored” are typically
those with extensively conjugated systems (typically
more than five)
• Consider b-carotene B-carotene, lmax = 455nm lmax is
at 455nm – in the far blue region of the spectrum – this
is absorbed.
The remaining light has the complementary color of
orange

• One of the most common class of colored organic
molecules are the azo dyes:
 lycopene, lmax = 474 nm O NH HN O indigo lmax for lycopene is
at 474 nm – in the near blue region of the spectrum – this is absorbed,
compliment is now
red lmax for indigo is at 602 nm – in the orange region of the
spectrum – this is absorbed, the compliment is now indigo!
 Sunset Yellow (Food Yellow 3) Visible Spectroscopy
 These materials are some of the more familiar colors of our “environment”

What does the detector in an UV-Vis absorption spectrophotometer
actually detect in the UV-Vis absorption spectroscopic experiment?
UV–Vis spectrometers are used to measure the reflectance of light,
and can be analyzed via the Forouhi–Bloomer dispersion equations
to determine the Index of Refraction (n) and the Extinction
Coefficient (k) of a given film across the measured spectral range.

What is the difference between a UV spectrophotometer
and a VIS spectrophotometer?
There is no difference between UV and visible
spectrophotometer because both these names are used for the
same analytical instrument.
This instrument uses the absorption spectroscopy technique in
Ultraviolet and visible spectral region.

How do you use UV-Vis spectrophotometer?
1. Fill the cuvette with the sample. ...
2. Place the cuvette in the spectrometer in
the correct direction.
3. Cover the cuvette to prevent any ambient light.
4. Sect an absorbance spectrum by allowing the
instrument to scan through different wavelengths
and collect the absorbance.

What is the difference between AAS and UV-Vis?
The key difference between atomic absorption
spectroscopy and UV visible spectroscopy is that atomic
absorption spectroscopy is based on the absorption of
light by atoms or ions, whereas UV visible spectroscopy
involves the absorption or reflectance of a part of the UV
range and complete adjacent visible regions of the.

What is the difference between IR and UV spectroscopy?
The area alongside with a longer wavelength is the IR
spectrum.
The area next to the visible light, with a shorter wavelength,
is the UV spectrum. Each wavelength transports a certain
amount of energy. The faster the frequency of these waves,
the shorter the wavelength and the more energy the radiation
can transport.

INFRARED (IR) SPECTROMETRY
INSTRUMENTATION OF INFRARED SPECTROSCOPY
1. Infrared (IR) Spectroscopy IR deals with the interaction of
infrared radiation with matter.
2. The IR spectrum of a compound can provide important
information about its chemical nature and molecular structure.
3. Most commonly, the spectrum is obtained by measuring the
absorption of IR radiation, although infrared emission and
reflection are also used.
4. Widely applied in the analysis of organic materials, also useful
for polyatomic inorganic molecules and for organometallic
compounds.

INFRARED REGION
1. Near Infrared Or Overtone: 1.2 -2.5 μm
2. Mid Infrared Or Vibration: 2.5 - 25 μm
3. Far Infrared Or Rotation: 25 - 400 μm

INSTRUMENTATION
SOURCE → SAMPLE →MONOCHROMATOR →DETECTOR →
READOUT
Instrumentation of IR spectrophotometer (PRINCIPLE)
 When energy in the form of infrared radiation is applied
 then it causes the vibration between the atoms of the molecules
and when,
 Applied infrared frequency = Natural frequency of vibration Then,
 Absorption of IR radiation takes place and a peak is observed.
 Different functional groups absorb characteristic frequencies of
IR radiation.
 Hence gives the characteristic peak value.
 Therefore, IR spectrum of a chemical substance is a finger print
of a molecule for its identification.

Source
•Nernst Glower •Globar •Incandescent wire source •Hg Arc
Monochromator
Grating Filter
Detector
Thermal D
Thermocouple
Thermopile
Thermister Bolometer
Pyroelectric D

 IR radiation source Be continuous over the wavelength range
used.
 Cover a wide wavelength range. Be constant over long
periods of time.
 The Nernst Glower They electrically heated to about 2000°C.
 It composed of a mixture of rare earth oxides such as
zirconium oxide (ZrO2), yttrium oxide (Y2O3) and thoria.
 Sealed by a platinum leads to the ends to permit electrical
connection. Consist of cylindrical hollow rod or tube having
a diameter of 1-2 mm and length of 30mm.
 Its lifetime depends on the operating temperature and the
care taken in handling it. It provides maximum radiation
about 7100cm-1

 Characteristics of IR Source
IR radiation source:
1. Be continuous over the wavelength range used.
2. Cover a wide wavelength range.
2. Be constant over long periods of time.

 Characteristics of The Nernst Glower
1. They are electrically heated to about 2000 °C.
2. It composed of a mixture of rare earth oxides such as
zirconium oxide (ZrO2), yttrium oxide (Y2O3) and thoria.
3. sealed by a platinum leads to the ends to permit
electrical connection.
4. Consist of cylindrical hollow rod or tube having a
diameter of 1- 2 mm and length of 30 mm.
5. its lifetime depends on the operating temperature and
the care taken in handling it.
6. It provide maximum radiation about 7100cm-1 (1.4 μ)

 Characteristics of The Globar source:
1. The Globar source: The power consumption is normally higher than
that of the Nernst Glower It provide maximum radiation about
5200cm-1.
2. Heated to about 2000°C.
3. It’s sintered silicon carbide rod, usually about 50mm in length
and 5 mm in diameter

4. convenient to use, more expensive & less
intense than Nernst Glower.
5. Water cooling is needed to cool the metallic
electrodes attached to the rod.

 Characteristics of The Mercury Arc.
The Mercury Arc.
1. In the UV and visible regions, this lamp emits atomic Hg
emission lines that are very narrow and discrete, but emits
an intense continuum in the far-IR region. When current
passes through the lamp, mercury is vaporized, excited, and
ionized, forming a plasma discharge at high pressure.
2. It is a high pressure mercury arc which consist of a quartz –
jacketed tube containing Hg vapor at P > 1 atm. Used for Far
IR region (wave no<200cm-1).

 Characteristics of Incandescent
1. Wire Source Incandescent wire sources are longer lasting
but of lower intensity than the glower or Globar.
 MONOCHROMATORS
1. Prism:-
• Used as dispersive element.
• Constructed of various metal halide salts
• Sodium chloride is most commonly prism salt used.
• These salts are subjected to mechanical & thermal
instability or water solubility.
• Protection against damage must be continuously
exercised.

Characteristics of Grating
1. Gratings are nothing but rulings made on some materials
like glass, quartz or alkyl halides depending upon the
instrument,
2. The mechanism is that diffraction produces
reinforcement.
3. The rays which are incident upon the gratings
gets reinforced with the reflected rays.

Advantages over Prism:
1. Made with materials like aluminum which are not
attacked by moisture. Used over considerable
wavelength range.
2. Sample cell & Sampling of substance Infrared spectra
may be obtained for gases, liquids or solids (neat or in
solution)
3. Material containing sample must be transparent to the
IR radiation. So, the salts like NaCl, KBr are only used.

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