Analytical chemistry

Analytical chemistry is the analysis of material samples togain an understanding of their chemical composition and structure .

Types

Analytical chemistry can be split into two main types:

1. Qualitative analysis seeks to establish the existence of a given element or compound .
2. Quantitative analysis seeks to establish the amount of a given element or compound .

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. Thelatter is of particular interest in biological systems; the molecules of life contain carbon, hydrogen, oxygen, nitrogen, andothers, in many complex structures.

Techniques

There are a bewildering array of techniques available to separate, detect and measure chemical compounds.

• Separation of chemicals in order to measure theweight or volume of a final product. This is an older process and can be quite painstaking.
• Analysis of substances with devices using spectroscopy . Measuring theabsorption of light by a solution or gas, we can calculate the amounts of several species, often without separation. Newermethods include atomic absorptionspectroscopy (AAS), Nuclear MagneticResonance (NMR) and neutron activationanalysis (NAA).
• Many techniques combine two or more analytical methods. Examples of this include ICP-MS (Inductively-Coupled Plasma - Mass Spectrometry), where volatilisation of a sample occurs in the first step, and measuring of the concentration occurs in thesecond. The first step may also involve a separation technique, such as chromatography , and the second a detection / measuring device.
• Techniques that involve volatilisation aim to produce free atoms of the elements making up the sample, which can then bemeasured in concentration by the degree to which they absorb or emit at a characteristic spectral frequency. These methods havethe disadvantage of completely destroying the sample, and any species contained within it. These techniques include [(atomicabsorption spectroscopy)] and [(ICP-MS / ICP-AES)]. These techniques can still be used to study speciation, however by theincorporation of a separation stage before volatilisation.

Methods

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, andequipment 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 bediluted in a pure solvent. If the amount in the sample is below an instrument's range of measurement, the method of addition canbe used. In this method a known quantity of the element or compound under study is added, and the difference between theconcentration added, and the concentration observed is the amount actually in the sample.

Trends

A lot of effort is put in shrinking the analysis techniques to chip size. ( TAS )

See also

• Importantpublications in analitical chemistry