intrumental analysis chap 1_introduction
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DESCRIPTIONChapter One : Introduction Instrumental Analysis.
Instrumental Techniques for
Chapter 1 : Introduction
Environmental Science and Technology
Jessore Science and Technology University
Analytical chemistry; its scope and application;
instruments for analysis,
representative sample; sample storage, its pre-treatment and
calibration of instrumental methods;
selecting an analytical methods
Skoog, Holler & Crouch 2007,
Instrumental Analysis, Brooks Cole
Cengage Learning, USA.
Gray, Cakvin & Bhatia, 2009,
Instrumental Methods of Analysis, 1st
edition, CBS, New Deli, India
Analytical Chemistry deals with methods
for determining the chemical composition
of samples of matter.
A qualitative method yields information
about the identity of atomic or molecular
species or the functional groups in the
A quantitative method provides numerical
information as to the relative amount of
one or more of these components.
Classification of analytical
sometimes called wet-
preceded by a century or more
Gravimetric or by volumetric
physical properties as conductivity,
light absorption or
paralleled the development of the
Types of instrumental methods
Electrical charge coulometry
Electrical current Amperomtry; palaeography
Instruments for analysis
An instrument for chemical analysis converts information about the physical or chemical
characteristics of the analyte to information
that can be manipulated and interpreted by a
An analytical instrument can be viewed as a communication device between the system
under study and the investigator.
To retrieve the desired information from the analyte, it is necessary to provide a stimulus,
which is usually in the form of
electromagnetic, electrical, mechanical, or
The measurement process is aided by a wide
variety of devices that convert information from
one form to another.
It is important to understand how information can
be encoded (represented) by physical and
chemical characteristics and particularly by
electrical signals, such as current. voltage, and
The various modes of encoding information are
called data domains.
types of domain
Nonelectrical domains The measurement process begins and ends
in nonelectrical domains.
The physical and chemical information / characteristics are length, density, chemical composition, intensity of light. pressure, and etc.
The information representing the mass of the object in standard units is encoded directlyby the experimenter who provides information processing by summing the masses to arrive at a number.
Home task: TABLE 1-2 Some Examples of Instrument Components
Data domain Map
Electrical domains The modes of encoding information as electrical
quantities are :
the digital domain
the measurement of the molecular fluorescence intensity of a sample of tonic water containing a
trace of quinine
The intensity of the fluorescence is significant in this context because it is proportional to the
concentration to the quinine in the tonic water,
which is ultimately the information that we desire.
A block diagram of fluorometer
(a) a general diagram of the instrument,
(b) a diagrammatic representation of the flow of information through
various data domains in the instrument
(c) the rules governing the data-domain transformations during the
The intensity of the fluorescence
emission, which is nonelectrical
information, is encoded into an
electrical signal by a special type of
device, called an input transducer.
In this example, the input transducer converts the fluorescence from the tonic water to an
electrical current I, proportional to the
intensity of the radiation.
The current is then passed through a resistor R, which according to Ohm's law produces a
voltage V that is proportional to I, which is in
turn proportional to the intensity of the
The mathematical relationship between the electrical output and the input radiant power impinging on its surface is called the transfer function of the transducer
Finally, V is measured by the digital voltmeter to provide a readout proportional to the concentration of the quinine in the sample. Devices that serve to convert data from
electrical to non-clectrical domains are called output transducers e.g. Voltmeters, alphanumeric displays, electric motors, computer screens
is encoded as the
magnitude of one of the
electrical quantities -
voltage, Current, charge,
These quantities are
continuous in both
amplitude and time.
Magnitudes of analog
quantities can be
they can be sampled at
specific points in time
dictated by the needs at
a particular experiment
Information is stored in the
time domain as the time
relationship of signal
The time relationships
between transitions of
the signal from HI to LO
or from LO to HI contain
the information of
For instruments that
produce periodic signals,
the number of cycles of
the signal per unit time
is the frequency and the
time required for each
cycle is its period.16
Data are encoded in the
digital domain in a two-
The characteristic that
these devices share is that
each of them must be in
one of only two states.
For example, lights and
switches may be only ON
or OFF and logic-level
signals may be only HI or
The measurement task is
to count the pulses during
a fixed period of time
Detector refers to a mechanical, electrical or chemical device that
identifies, records. or indicates a
change in one of the variables in its
pressure, temperature, electrical charge, electromagnetic radiation, nuclear radiation.
An example is the UV (ultraviolet) detector often used to indicate and
record the presence of eluted analytes
in liquid chromatography.
those devices that convert
information in nonelectrical
domains to information in
electrical domains and the
other electronic photodetectors
analytical devices that are
capable of monitoring specific
chemical species continuously
the glass electrode
the Clark oxygen electrode, and
liber-optic sensors (optrodes)
Sensors consist of a transducer
coupled with a chemically
selective recognition phase.
A readout device is a transducer that
converts information from an
electrical domain to a form that is
understandable by a human observer.
Usually, the transduced signal takes
the form of
the alphanumeric or graphical output of a cathode-ray tube,
a series of numbers on a digital display,
the position of a pointer on a meter scale,
a tracing on a recorder paper.
Computer in instruments
Most modern analytical instruments contain or are
attached to one or more
sophisticated electronic devices
and data-domain converters.
operational amplifiers,integrated circuits,analog-to-digital digital-to-analog converters, microprocessors, andComputers.
A complete analysis
five main steps:
Sampling; selecting a representative sample of the
material to be analyzed
Dissolution of the sample
Conversion of the analyte into a form suitable for measurement
Calculation and interpretation of the measure.
The aims of analysis are understood and an appropriate