MEV 013: Unit 12 - Basic Analytical Techniques

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UNIT 12: BASIC ANALYTICAL TECHNIQUES

12.0 Introduction

Analytical techniques are fundamental to the study of chemistry, environmental science, materials science, biology, and many other disciplines. These methods help identify, separate, quantify, and determine the composition and structure of substances. In environmental studies, accurate analysis is essential for assessing pollution levels, monitoring ecosystem health, and ensuring compliance with environmental standards.

12.1 Objectives

After studying this unit, you will be able to:

  • Understand the significance of analytical techniques.
  • Classify the various analytical methods.
  • Describe the principles behind chemical, electrical, optical, nuclear, and thermal analyses.
  • Evaluate analytical data for errors, accuracy, and precision.
  • Properly report results using correct chemical and numerical expressions.

12.2 Analytical Techniques: Importance

Analytical techniques are essential for:

  • Environmental monitoring (e.g., detecting pollutants in air, water, and soil).
  • Quality control in industry.
  • Biomedical analysis (e.g., blood or tissue testing).
  • Forensic science.
  • Research and development of new materials.

They provide qualitative (what is present) and quantitative (how much is present) information about substances.

12.3 Classification of Analytical Techniques

Analytical techniques can be broadly categorized into the following:

12.3.1 Chemical Methods of Analysis

These involve chemical reactions to determine the presence or concentration of a substance.

  • Titration (acid-base, redox, complexometric)
  • Gravimetric analysis
  • Precipitation reactions

Advantages:

  • Inexpensive and simple
  • Suitable for routine analysis

Limitations:

  • Less sensitive
  • Time-consuming

12.3.2 Electrical Methods of Analysis

These rely on electrical properties such as voltage, current, and resistance.

  • Conductometry – measures conductivity
  • Potentiometry – uses electrodes to measure voltage (e.g., pH meter)
  • Voltammetry – measures current produced during electrochemical reactions

Useful for:

  • Trace analysis
  • Monitoring ionic concentrations

12.3.3 Optical Methods of Analysis

These use light absorption, emission, or scattering.

  • UV-Visible Spectroscopy
  • Infrared (IR) Spectroscopy
  • Atomic Absorption Spectroscopy (AAS)
  • Fluorescence Spectroscopy
  • Colorimetry

These methods are widely used in detecting pollutants, organic compounds, and metals in environmental samples.

12.3.4 Nuclear Methods

These involve the interaction of radiation with matter.

  • Neutron Activation Analysis (NAA)
  • X-ray Fluorescence (XRF)
  • Radiometric techniques

Applications:

  • Trace element detection
  • Geological and environmental studies

12.3.5 Thermal Methods of Analysis

These involve changes in physical and chemical properties as a function of temperature.

  • Thermogravimetric Analysis (TGA)
  • Differential Thermal Analysis (DTA)
  • Differential Scanning Calorimetry (DSC)

Used to study:

  • Decomposition patterns
  • Thermal stability
  • Reaction kinetics

12.4 Criteria for Evaluating Analytical Techniques

When selecting an analytical method, consider:

  • Sensitivity: Ability to detect low concentrations
  • Selectivity: Ability to distinguish a substance from other components
  • Precision: Reproducibility of results
  • Accuracy: Closeness to the true value
  • Cost and ease of operation
  • Time efficiency
  • Availability of instruments and reagents

12.5 Evaluation of Analytical Data

Analytical results must be evaluated to ensure reliability and validity.

12.5.1 Errors and Detection of Errors

Errors can be classified as:

  • Systematic errors (constant or predictable; can be corrected)
  • Random errors (unpredictable variations)

Sources of errors:

  • Instrumental (e.g., faulty calibration)
  • Methodological (e.g., incorrect reagent concentration)
  • Human (e.g., misreading data)

Detection methods:

  • Performing replicates
  • Using blanks
  • Calibration with standards

12.5.2 Accuracy and Precision

  • Accuracy: How close a measurement is to the actual value.
  • Precision: The consistency of repeated measurements.

Example:

  • A measurement close to the true value is accurate.
  • A set of repeated values that are close to each other (regardless of their accuracy) is precise.

Ideal measurements are both accurate and precise.

12.6 Reporting of Results

The final stage in analysis involves presenting the data clearly and accurately.

12.6.1 Chemical Expression of Results

Expressed as:

  • Molarity (mol/L)
  • Normality (eq/L)
  • Parts per million (ppm) or billion (ppb)
  • Mass concentration (mg/L)

12.6.2 Numerical Expression of Results

Results should include:

  • Mean (average) value
  • Standard deviation
  • Relative error or percentage error

12.6.3 Significant Figures

  • Report results with the correct number of significant figures, based on the precision of the measuring instrument.
  • Avoid over-reporting or under-reporting precision.

Example: If an instrument reads to the hundredths place, report the result as 3.46, not 3.45678 or 3.4.

12.7 Let Us Sum Up

In this unit, we have:

  • Understood the importance of analytical techniques in scientific and environmental studies.
  • Explored the classification of techniques: chemical, electrical, optical, nuclear, and thermal.
  • Reviewed how to evaluate analytical data, including sources of error, accuracy, and precision.
  • Learned how to report results accurately using chemical and numerical expressions.

Mastery of analytical techniques ensures reliable data collection and interpretation, which is vital for scientific progress and responsible environmental stewardship.

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