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How do we identify molecules?
Proving the identifiy of a molecule most often relies on multiple methods of quantitative analysis. Mass spectrometry is a powerful way to determine the mass of the parent ion (usually the whole molecule) and fragmentation products that can be interpreteed in terms of known tendencies of molecules to break apart when ionized in the mass spectrometer. Mass spectrometery relies on the ability to ionize a molecule since only changed species can be manipulated using magnetic fields in order to dtermine their mass. Elemental analysis is useful for identifying the elements present and their relative percentages. In an indectibely-coupoed plasma (ICP atomic emission analyzer one can determine trace amounts of elements presentin a sample as well as obtaining an overall descriptoin of the compositoin. Thermogravimetric analysis can provide information on thermal deomposiotn products, which are characteristic for certain compounds and provide information relevant to their stability for applications. Routine ultraviolet (UV) visible absorption spectrometry is a routine method for rapid analysis of molecules in the laboratory. It is the most common way to determine concentraion on a routine basis. The methods we consider here characterize all aspects of molecules except their struture. X-ray crstallography and nuclear magnetic resonance (NMR) deserve mention, but these will be discussed in more advanced courses. Taken together these methods give us a set of tools that we can use to identify molecules unknowns and describe molecule properties in useful ways for technology and discovery of new properties.
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