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How does chemical analysis determine the composition of a sample?

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A strip of pH paper rests on the rim of a container holding a yellow liquid, with a color comparison chart and several unused pH strips nearby. — chemical analysis Strip of pH paper resting on specimen, with a comparison chart.

Chemical analysis determines the composition of a sample by employing a combination of qualitative and quantitative methods to identify and measure its constituents.12

Qualitative Analysis

This branch focuses on identifying the elements or groups of elements present in a sample. Techniques range from simple tests, such as flame tests to detect specific elements, to systematic procedures for complex mixtures. For example, organic compounds are often analyzed by observing their behavior when heated, while inorganic samples may be dissolved and treated with reagents to separate and identify specific cationic or anionic constituents.32

Quantitative Analysis

Once constituents are identified, quantitative analysis measures their specific amounts or percentages. Common approaches include:12
* Chemical Methods: Techniques like gravimetric analysis and volumetric analysis rely on reactions such as precipitation or neutralization.1
* Physical Methods: These involve measuring properties like density, refractive index, or light absorption.1
* Instrumental Techniques: Sophisticated tools like mass spectrometry sort ions by their mass-to-charge ratios, while chromatography separates components based on their distribution between mobile and stationary phases. Spectrochemical analysis further determines composition by measuring the intensity and wavelength of electromagnetic radiation emitted or absorbed by atoms.456