Chemical analysis is valuable in chemical research, industry, archeology, medicine, and many other fields. A representative sample must first be taken and prepared for analysis. Preliminary separation is often carried out by chromatography, ion exchange, distillation, or precipitation.
In qualitative analysis, classical methods involve characteristic reactions of substances. After preliminary tests – inspection, heating, and flame tests – systematic schemes are followed which separate the various ions into groups according to their reactions with standard reagents, and which then identify them individually. Cations (positive ions) and anions (negative ions) are analyzed separately. For organic compounds, carbon and hydrogen are identified by heating with copper (II) oxide, carbon dioxide and water being formed; nitrogen, halogens, and sulfur are identified by heating with molten sodium and testing the residue for nitrile, halides, and sulfide, respectively. Classical quantitative analysis is performed by gravimetric analysis and volumetric analysis.
Modern chemical analysis employs instrumental methods to give faster, more accurate assessments than do classical methods. Many modern methods have the additional advantage of being nondestructive. They include colorimetry, spectrophotometry, polarography, mass spectrometry, differential thermal analysis, potentiometric titration (see potentiometer, and methods for determining molecular weight. Neutron activation analysis subjects a sample to neutron irradiation and measures the strength of induced radioactivity and its rate of decay. In X-ray analysis, a sample is irradiated with X-rays and emits X-rays of different, characteristic wavelengths (see X-ray crystallography.
Related category• ANALYTICAL CHEMISTRY
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