Analtical Techniques

There are 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 emmision of light by a substance we can calculate the amounts of species or characterize the chemical species, often without separation. Newer methods include 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" or "hybrid" 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 the second. 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 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 volatilisation.

• Another example of a hybrid technique is Gas Chromatography-Mass Spectrometry [GC/MS], which is primarily used for non-ionic, volatilizable organic compounds. The compounds are separated on a chromatographic column, and introduced directly, or via a specialized interface, to an ionization chamber in a mass spectrometer. The compounds are then ionized (typically by electron impact, or chemical ionization) and accelerated through a carefully controlled electromagnetic field. The time of flight, or the voltage applied at the exact moment of impact is unique for compounds of the same mass. In this manner, the retention time and mass are meaured for each compound.