The two important objectives of analytical chemistry are the identification of substances and the determination of their concentration (qualitative and quantitative analyses respectively). Spectro- analytical methods offer an excellent way of fulfilling both of these objectives:

1. Identification of substances:

When a beam of electromagnetic radiations of different wave­lengths are directed through a sample one after the other some wave-lengths are absorbed more effectively than others and some may not be absorbed at all. The resultant Absorption spectrum is characteristic for the substance concerned.

The maximum absorption by the sample or absorption maxima always occurs at a fixed wave length. Other lesser absorption peaks also occur at their respective wave-lengths only. Similarly, when the sample is so excited as to produce radiations, it produces more intense radiations at certain wave-lengths and nominal or very dim radiations at others.

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The resultant emission spectrum is also characteristic for the substance concerned – the emission of maximum intensity occurring at a definite wave-length only. Therefore, both absorption and emission spectra of a substance offer possibility of chemical identification from the characteristic emission or absorption patterns.

2. Determination of concentration of absorbing substances:

Most of the spectroanalytical methods are based either on absorption or emission of radiations which is an intrinsic property of matter. The spectrum which is obtained is due to the absorption or emission of radiant energy by a large number of atoms or molecules.

The intensity of radiation absorbed or emitted, as the case may be, vary with concentration of absorbing or emitting material in the sample. The phenomenon, therefore, provides us with a means to estimate the concentration of substance simply by comparing the intensity of radiations emitted or by the degree upto which it is absorbed by the sample.

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A very simple technique of comparison of the unknown sample with that of standard or known sample is used to determine the concentration of the substance concerned in spectroanalytic methods. Absorbance or emission of a series of standard solutions or known amounts of substance is obtained. A graph is plotted of intensities obtained against concentration of the substance in the sample. The absorbance or emission of the unknown sample is then determined and the concentration of the substance in the sample is read from the graph on the other axis.