Activity of detergents in dry cleaning

The main component of detergents is surfactant. The eldest known surfaetant is soap. Chemically soap is an alkaline salt of fatty acid. Characteristic of soap (and surfactant) is the molecular structure consisting of apolar - hydrophobic - part (fatty acid) and a polar - hydrophilic - part (-COONa), causing surface activity in aqueous solution. 

Surface activity has its function in the insolubility of the hydrophobic part of molecule in water and the hydrophilic part of molecule influences water solubility. This gives a tension within soap molecules in water forming layers on every available surface and forming micelles if there is a surplus of soap molecules compared to the available surface. This soap behavior stands as an example of mechanism of action of surfactants in general. 

Micelles of surfactants in water are formed by molecular aggregates of surfactants oriented in such a way that the hydrophobic parts are directed internally, so that the hydrophilic parts are directed outwards. In this way the aggregates form spheres, cylinders, or laminar layers, dependent on its concentration. 

Emulsions in this case are not formed by oil in water, but by water in oil (solvent). 

Because of this behavior, it is possible to remove water soluble (polar) material from substrates in solvents, if surfactants are at present. The surfactants disperse the polar material into very small particles and build up micelles around the particles, so that the polar material is totally incorporated inside micelle. If the aggregates are small, the solution is clear. If they are large, the solution (emulsion -type water in oil) becomes milky. 

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The most important and usually the most effective constituent of a cleaning aid is a surface-active substance. Historically, six classes of surfactants have been used in dry cleaning detergents [11] ... 

Cleaning of the sample containers is also different in that no organic solvents are used. The septa and vials are cleaned in hot detergent water and rinsed repeatedly with hot distilled water. They are then dried in a clean oven at 100 °C for one hour. The screw caps with septa are then placed on the vials while still warm. The empty vials are then sealed in clean wide-mouth jars over a layer of activated carbon and transported to the sampling site. The crimp top vials are handled in an analogous manner but the tops are not crimped down. 

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