149.Methods of Analysis.

Analytical chemistry is all about analysis. In this post, we shall look at the various methods of analysis that we encounter in this branch of chemistry.

Analysis can be of two types –

1)Qualitative analysis – This helps in answering the question ‘What is present‘ in the sample? In short, qualitative analysis reveals the identity of the elements/compounds in the sample.

2)Quantitative analysis– This analysis helps us to answer the question ‘How much is present‘? This analysis helps us to find out the amount of analyte in the sample.

However, most of the time, in the course of analysis, both qualitative and quantitative information is needed. For example, suppose we are analyzing pollutants in water. We need to know which substances(qualitative) are the pollutants and what is their concentration(quantitative).

The measurement stratagies are based on the measuring either of the following three parameters –

1) Physical property
2)Interaction with electromagnetic radiation – spectroscopy.
3)Electric charge/current.

Physical PropertySpectroscopyElectric charge/current
Mass or volumeAbsorptionElectrical conductivity
DensityEmissionElectrical potential
e.g.-pH meter
Refractive indexScatteringVoltammetry
Freezing point depressionMass spectrometry
Thermal conductivity

To choose among any one of these three general strategies for a given problem depends on the nature of the analyte and the sample matrix.

We can also broadly classify the methods of analysis as follows-

Classical methods

Classical methods are routine, simple methods that are used in laboratories. They are simple procedures and cost-effective. They do not need sophisticated instruments and so these methods are preferred where high accuracy is not essential. The classical methods can be subdivided into two types namely –

Gravimetric analysis – This method involves the quantitative measurement of the analyte through the measurement of mass. This method involves determining the mass of the analyte or some compound chemically related to it.
Volumetric analysis – This method involves titrations. The volume of a solution containing sufficient standard reagent to react completely with the analyte is measured.

Instrumental methods

As the name suggests, these methods involve use of instruments. These involve very accurate measurements. Some physical property of the analyte is measured by an instrument, which gives us information about the analyte. Depending on the physical property under study, the instrumental methods can be broadly classified as –

Optical methods – These are based on the interaction of the analyte with electromagnetic radiations(i.e light).
Electroanalytical methods – These involve measuring some electric property(e.g.conductance, electrical potential, etc) of the analyte.
(We will be learning all these methods in detail later. Therefore, I am not explaining them here. This is just an overview of the general methods of analysis).

Choosing a method is sometimes difficult as it requires expertise and intuition.

Separation techniques

When we deal with samples in analytical chemistry, it is imperative that we first separate the component of interest from the sample matrix. Matrix is all components in the sample containing the analyte.

Two main types of separation techniques are – Solvent extraction and Chromatography

Solvent extraction – Different substances have different solubilities in solvents. This technique uses this variation in solubilities to separate the analyte from the matrix.

Chromatography – This is a physical method for the separation of components of a mixture by passing it through a medium in which the components move at different rates.

We will be learning all these methods in detail later. This is just an overview of the general methods of analysis. In the next post, we will learn another concept in analytical chemistry.Till then,

Be a perpetual student of life and keep learning….

Good day !

References and Further Reading –

1.Basics of Analytical Chemistry and Chemical Equilibria by Brian M. Tissue.

2,1.Principles of Instrumental Analysis 6th Edition by Douglas A. Skoog, F. James Holler, and Stanley R. Crouch.

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