Separation science is the science used by a laboratory to separate a mixture of components into batches of related components. This can be as simple as extracting all of the oil from a sea water sample (Gulf of Mexico oil spill) or as complex as separating all 16,000+ components from a diesel sample. This can be done by applying many difference approaches from the extremely simple such as gravity or density, distillation or evaporation to more complex approaches such as GC and GC×GC.
When a mixture is created, any components that will react will form new substances, the rest remain the same. Some will degrade fast, others will degrade slowly over time. However, once the mixture “settles”, generally no further reactions occur, nor will bonds be created. At such a time mixtures can then be separated back into their component parts. An easy example is using colours, where yellow and blue will make green. With the right combination of chemicals it is possible to separate green back into blue and yellow.
Of course, once you have separated the substances, you will need to identify these to confirm that you have performed the task properly.
What is Chromatography, then?
Separation science and chromatography are often used interchangeably in the modern laboratory context as the older techniques have been ingrained in the sub-conscious. For example, using a centrifuge is a form of separation science that is so common that it is “no longer” seen as a separation science technique.
Chromatography is derived from the Greek words for colour, “chroma” and writing “graphein”. A Russian scientist, Mikhail Tsvet, developed this technique in 1900 when working on pant pigments such as carotenes and chlorophyll. As these pigments have different colours, the act of separating these on a paper made the process appear to be writing colours on the paper, hence the name. This is still a beautiful experiment that can be duplicated.
The field of chromatography nowadays underpins the sciences of chemistry and biology, as well as the bridging field of biochemistry and naturally engineering. Most modern fields such as genomics, DNA fingerprinting, drug discovery and even nutrition and diet owe their modern existence to
Separation science is also referred to as “chromatography”, a term which combines the Greek words for colour (“chroma”) and writing (“graphein”). The various techniques and methods which underpin separation science inform the study of chemistry and biology, as well as engineering. Major advances in separation science have enabled biologists, chemists, pharmacists and environmentalists to make breakthroughs of their own. Genomics, drug discovery, DNA fingerprinting and ultra-trace residue analysis, for instance, would not be possible without recourse to the findings generated by separation science.
Different Types of Separation Science: preparative and analytical chromatography
Separation science, or chromatography, can be analytical or preparative. Analytical chromatography relies on small amounts of material and strives to measure the relative amounts of analytes in a mixture. No attempt is made to ready the material for future use.
Preparative chromatography, on the other hand, seeks to separate a mixture into usable component parts. Preparative chromatography can be done on a small scale or an industrial scale.
Separation processes need to be devised with the end goal in mind. Nearly every single element or compound in nature is found as a mixture, whether something as simple as gold in ore or even the impurties in gold to the much more complex petrochemicals. Indeed, the body is a mixture of over 4,000 chemicals! The role of separation science is to pull these chemicals into a number of pure components – or rather – pure enough components. Perfection in separation science is not always a requisite and a fit-for-purpose separation that meets the quality and cost criteria is critical.
Typically in gas chromatography, the separation process is based on differences in physico-chemical properties such as boiling point or polarity, though one must remember that size-exclusion or chirality are just as valid properties. Sometimes multiple operations are performed to achieve the desired separation, which is where multidimensional comprehensive chromatography (GC×GC) comes into play.