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Chapter One : Introduction Instrumental Analysis.

TRANSCRIPT

  • Instrumental Techniques for

    Environmental Analysis

    Chapter 1 : Introduction

    Rezaul Karim

    Environmental Science and Technology

    Jessore Science and Technology University

    1

  • Chapter outline

    Analytical chemistry; its scope and application;

    instrumental analysis;

    instruments for analysis,

    representative sample; sample storage, its pre-treatment and

    preparation,

    sample pre-treatment,

    calibration of instrumental methods;

    selecting an analytical methods

    2

  • Reference

    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

    3

  • Analytical chemistry

    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

    sample.

    A quantitative method provides numerical

    information as to the relative amount of

    one or more of these components.

    4

  • Classification of analytical

    methods

    Classical

    methods

    sometimes called wet-

    chemical

    method

    preceded by a century or more

    Gravimetric or by volumetric

    measurements

    Instrumental

    methods

    physical properties as conductivity,

    electrode potential,

    light absorption or

    emission, mass-to-

    charge ratio

    paralleled the development of the

    electronics and

    computer

    industries.

    5

  • Types of instrumental methods

    Characteristic

    Properties

    INSTRUMENTAL

    METHODS

    Radiation

    e.g. Emission,

    adsorption,

    scattering, refracting,

    rotating,

    Diffraction, refraction

    Spectrophotometer and

    photometry

    Electrical charge coulometry

    Electrical current Amperomtry; palaeography

    Mass Gravimetric

    6

  • 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

    human.

    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

    nuclear energy.

    7

    responseStimulus

    System

    under study

  • Data domain

    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

    charge.

    The various modes of encoding information are

    called data domains.

    types of domain

    nonelectrical domains

    electrical domains8

  • 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

    9

  • Data domain Map

    10

  • Electrical domains The modes of encoding information as electrical

    quantities are :

    analog domains

    time domains,

    the digital domain

    For example,

    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.

    11

  • A block diagram of fluorometer

    12

    (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

    measurement process.

  • 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

    fluorescence.13

  • 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

    14

  • Analog-Domain Signals

    is encoded as the

    magnitude of one of the

    electrical quantities -

    voltage, Current, charge,

    or power.

    These quantities are

    continuous in both

    amplitude and time.

    Magnitudes of analog

    quantities can be

    measured continuously,

    they can be sampled at

    specific points in time

    dictated by the needs at

    a particular experiment

    or instrumental.

    15

  • Time-Domain Information

    Information is stored in the

    time domain as the time

    relationship of signal

    fluctuations.

    The time relationships

    between transitions of

    the signal from HI to LO

    or from LO to HI contain

    the information of

    interest.

    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

  • Digital information

    Data are encoded in the

    digital domain in a two-

    level scheme.

    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

    LO.

    The measurement task is

    to count the pulses during

    a fixed period of time

    17

  • Detector

    Detector refers to a mechanical, electrical or chemical device that

    identifies, records. or indicates a

    change in one of the variables in its

    environment, e.g.

    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.

    18

  • Transducer

    those devices that convert

    information in nonelectrical

    domains to information in

    electrical domains and the

    converse.

    photodiodes,

    photomultipliers, and

    other electronic photodetectors

    19

  • Sensor

    analytical devices that are

    capable of monitoring specific

    chemical species continuously

    and reversibly.

    the glass electrode

    ion-selective electrodes,

    the Clark oxygen electrode, and

    liber-optic sensors (optrodes)

    Sensors consist of a transducer

    coupled with a chemically

    selective recognition phase.

    20

  • Readout device

    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.

    21

  • 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.

    22

  • 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

    Measurement and

    Calculation and interpretation of the measure.

    23

  • Representative sample

    The aims of analysis are understood and an appropriate