Hobbies And Interests
Filtration Processes
Chemists often employ filtration in order to separate solid/liquid mixtures. In this process, a technician places filter paper in a specially designed funnel and pours a liquid/solid mixture over the paper. The solid remains on top of the paper as the liquid drips through to a collection flask. Labs sometimes use a specially designed Buchner funnel, which allows them to apply a vacuum to the filtration system during filtration. This makes the rate of filtration much quicker.
Chromatography
Chromatography -- literally meaning "color writing" -- was first used to separate plant pigments. In this technique a mixture of chemicals is forced through a tube containing a porous solid matrix. Since different chemicals will have different affinities for that solid, they will travel through the tube at different rates and so exit at separate times. More modern versions include gas chromatography, in which a sample is volatilized into a gas and pushed through a tube on a flow of helium. In liquid chromatography, samples are dissolved in solvent and pumped through a separation tube.
Distillation
Distillation is an ancient practice, still widely used today in labs and industry. The concept is quite simple: A solid/liquid or liquid/liquid mixture is heated until the most volatile liquid (or the only liquid) boils. The resulting vapors are drawn off and re-condensed somewhere else, thus removing the liquid from the original mixture. This method is used to concentrate the alcohol in wines to make brandy and other strong drinks and also to separate fractions of petroleum.
Extraction
Extraction uses a solvent to pull a particular chemical out of a mixture of solid compounds. Labs perform an extraction by adding solvent to the mixture -- which dissolves the desired chemical -- then filtering off the remaining undissolved solids. The chemical can then be recovered from the solvent. The chemical being extracted might also be an impurity, which needs to be removed. An example of solvent extraction is the removal of caffeine from coffee beans. In the early days of decaf coffee, the organic solvent methylene chloride was used to extract caffeine. This approach is no longer used because of toxicity concerns about that solvent.
Electrophoresis
Electrophoresis works to separate large molecules, such as DNA or proteins. Technicians first dissolve the compounds to be separated in an aqueous buffer, which gives them a positive or negative charge, and then place some of the solution on a paper or gel support medium. An apparatus made up of a high-voltage power supply and electrodes creates an electric potential along the support, drawing the charged chemicals through the support and toward the electrodes. The chemicals move at different rates in response to the current, based on their individual charges and molecular weights, and so are separated.