Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. It has wide range of application from routine quality control in industrial settings to cutting edge chemical research in developing new compounds. Monitoring pollution in the environment, development of new materials, drug manufacture, and even forensic science all make use of techniques and methods developed in analytical chemistry. While the focus of this article is the functions in a laboratory setting, analytical chemistry is involved in many synthetic or man-made creations. As such, analytical chemistry is a foundational arena for the infinite unfolding of human creativity.
Analytical chemistry can be split into two main types, qualitative and quantitative:
- Qualitative inorganic analysis seeks to establish the presence of a given element or inorganic compound in a sample.
- Qualitative organic analysis seeks to establish the presence of a given functional group or organic compound in a sample.
- Quantitative analysis seeks to establish the amount of a given element or compound in a sample.
Most modern analytical chemistry is quantitative. Quantitative analysis can be further split into different areas of study. The material can be analyzed for the amount of an element or for the amount of an element in a specific chemical species. The latter is of particular interest in biological systems; the molecules of life contain carbon, hydrogen, oxygen, nitrogen, and others, in many complex structures.
There is a bewildering array of techniques available to separate, detect and measure chemical compounds.
- Separation of chemicals in order to measure the weight or volume of a final product. This is an older process and can be quite painstaking, but is an essential first step when dealing with certain mixtures of substances, like extracts from organisms. Modern separation techniques such as HPLC often seek to separate and determine amount or identity in a single automated analysis by integrating a detector.
- Titration is a technique used to determine amounts present in solution or a physical characteristic of a molecule such as an equilibrium constant.
- Analysis of substances with devices using spectroscopy. By measuring the absorption or emission of light by a substance we can calculate the amounts of species or characterize the chemical species, often without separation. Newer methods include infra-red spectroscopy (IR), atomic absorption spectroscopy (AAS), nuclear magnetic resonance (NMR) and neutron activation analysis (NAA).
- Mass spectrometry is used to determine the molecular mass, the elemental composition, structure and sometimes amount of chemical species in a sample by ionizing the analyte molecules and observing their behavior in electric and magnetic fields.
- Many techniques combine two or more analytical methods (sometimes called "hyphenated" methods). Examples of this include ICP-MS (Inductively-Coupled Plasma - Mass Spectrometry), where volatilization of a sample occurs in the first step, and measuring of the concentration occurs in the second. The first step may also involve a separation technique, such as chromatography, and the second a detection / measuring device.
- Techniques that involve volatilization aim to produce free atoms of the elements making up the sample, which can then be measured in concentration by the degree to which they absorb or emit at a characteristic spectral frequency. These methods have the disadvantage of completely destroying the sample, and any species contained within it. These techniques include atomic absorption spectroscopy and ICP-MS / ICP-AES. These techniques can still be used to study speciation, however by the incorporation of a separation stage before volatilization.
Analytical methods rely on scrupulous attention to cleanliness, sample preparation, accuracy and precision.
Many practitioners will keep all their glassware in acid to prevent contamination, samples will be re-run many times over, and equipment will be washed in specially pure solvents.
A standard method for analysis of concentration involves the creation of a calibration curve.
If the concentration of element or compound in a sample is too high for the detection range of the technique, it can simply be diluted in a pure solvent. If the amount in the sample is below an instrument's range of measurement, the method of addition can be used. In this method a known quantity of the element or compound under study is added, and the difference between the concentration added, and the concentration observed is the amount actually in the sample.
Analytical chemistry research is largely driven by performance (sensitivity, selectivity, robustness, linear range, accuracy, precision, and speed), and cost (purchase, operation, training, time, and space).
A lot of effort is put in shrinking the analysis techniques to chip size. Although there are few examples of such systems competitive with traditional analysis techniques, potential advantages include size/portability, speed, and cost (Total Analysis System or lab on a chip)
Much effort is also put into analyzing biological systems. Examples of rapidly expanding fields in this area are:
- Proteomics - the analysis of protein concentrations and modifications, especially in response to various stressors, at various developmental stages, or in various parts of the body.
- Metabolomics - similar to proteomics, but dealing with metabolites.
- Metalomics - similar to proteomics and metabolomics, but dealing with metal concentrations and especially with their binding to proteins and other molecules.
- Infra-red spectroscopy (IR)
- High performance liquid chromatography (HPLC)
- Gas-liquid chromatography (GC)
- Nuclear magnetic resonance (NMR)
- Mass spectrometry (MS)
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