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Potentiometric titration of surfactants without chloroform: Metrohm says that it is possible to test without using chloroform.

No matter how much fun we have squishing our toes in the mud, we love to be clean. We want our clothes to be fresh, our dishes to be spotless, and our cars to be shiny. We continue to invent new ways to make things clean, and soap was probably discovered only shortly after cooking, as the fats from the food hit the ashes from the fire.

Since then many different types of cleaning products have been developed.

A surfactant is a chemical that stabilizes mixtures of oil and water by reducing the surface tension at the interface between the oil and water molecules. These molecules contain both hydrophobic and hydrophilic components and are thus semi-soluble in both organic and aqueous solvents.

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Surfactants are the active ingredients in soap, since the hydrophobic component sticks to grease and dirt while the hydrophilic section sticks to the water. A surfactant has to be added to the mixture to keep it from separating into layers. Surfactants in cosmetics provide one or more of six functions:

* Detergents - for cleansing

* Wetting agents - in perms

* Foaming agents - for shampoos

* Emulsifiers - in creams and lotions

* Conditioning agents - in skin and hair-care products

* Solubilisers - for perfumes and flavours

Surfactants constitute the most important group of detergent components. Generally, these are water-soluble surface-active agents comprised of a hydrophobic portion, usually a long alkyl chain, attached to hydrophilic or water solubility enhancing functional groups.

In general, surfactants are divided into four classes: amphoteric, with zwitterionic head groups; anionic, with negatively charged head groups; cationic, with positively charged head groups; and nonionic, with uncharged hydrophilic head groups. Those with anionic head groups include long-chain fatty acids, sulfosuccinates, alkyl sulfates, phosphates, and sulfonates. Cationic surfactants may be protonated long-chain amines and long-chain quaternary ammonium compounds. The class of amphoteric surfactants is represented by betaines and certain lecithins, while nonionic surfactants include polyethylene oxide, alcohols, and other polar groups.

Detergents and soaps are used for cleaning because as discussed previously pure water can't remove oily, organic soiling. Soap cleans by acting as an emulsifier. Basically, soap allows oil and water to mix so that oily grime can be removed during rinsing. Detergents were developed in response to the shortage of the animal and vegetable fats used to make soap during World War I and World War II.

Modern detergents contain more than surfactants. Cleaning products may also contain enzymes to degrade protein-based stains, bleaches to de-color stains and add power to cleaning agents, and blue dyes to counter yellowing. Like soaps, detergents have hydrophobic or water-hating molecular chains and hydrophilic or water-loving components. The hydrophobic hydrocarbons are repelled by water, but are attracted to oil and grease. The hydrophilic end of the same molecule means that one end of the molecule will be attracted to water, while the other side is binding to oil. Neither detergents nor soap accomplish anything except binding to the soil until some mechanical energy or agitation is added into the equation. Swishing the soapy water around allows the soap or detergent to pull the grime away from clothes or dishes and into the larger pool of rinse water. Rinsing washes the detergent and soil away. Warm or hot water melts fats and oils so that it is easier for the soap or detergent to dissolve the soil and pull it away into the rinse water. Detergents are similar to soap, but they are less likely to form films (soap scum) and are not as affected by the presence of minerals in water (hard water).

Modern detergents may be made from petrochemicals or from oleochemicals derived from plants and animals. Alkalis and oxidizing agents are also chemicals found in detergents. Here's a look at the functions these molecules serve:

* Petrochemicals/Oleochemicals These fats and oils are hydrocarbon chains which are attracted to the oily and greasy grime.

* Oxidizers Sulpur trioxide, ethylene oxide, and sulphuric acid are among the molecules used to produce the hydrophilic component of surfactants. Oxidizers provide an energy source for chemical reactions. These highly reactive compounds also act as bleaches.

* Alkalis Sodium and potassium hydroxide are used in detergents even as they are used in soapmaking. They provide positively charged ions to promote chemical reactions. (1)

The determination of all these components both as raw materials and within a formulated mixture/product is important.

For many years now analysis of the anionic surfactants have been analysed using the Epton titration and this method has an accredited method noteably ISO 2271

If we take this ISO method, for example, the standard procedure is the two phase titration with the mixed indicator system disulfin blue and dimidium bromide

However, this procedure has many disadvantages: It can hardly be automated and must be carried out manually.

It uses chloroform or other chlorinated hydrocarbons.

The visual endpoint detection can be difficult, and the method is time consuming.

Metrohm offers an automated titration without the disadvantages of standard two-phase procedures when analysing anionic, cationic, or nonionic surfactants using the Metrohm Titrando

With the Titrando, and Metrohm's know-how the above titrations can easily be automated without the need for chloroform, or the other nasty indicators.

The anionic titration by potentiometric titration has recently been assigned DIN EN 14480.

Here are some examples of the titrations that can be performed;

* Anionic surfactants and soaps in washing powder.

* Anionic surfactants in dishwashing concentrates.

* Cationic surfactants in hair conditioner.

* Cationic surfactants in cooling lubricants.

* Nonionic surfactants in mouth rinse.

* Nonionic surfactants in household cleaners.

* Total phosphate in washing powders.

* Sulphate in washing powders.

* Betains by titration.

* Polyacrylates by titration.

Metrohm has also released the Surfpac, a library of methods and techniques for the automated analysis of surfactants.

This is a comprehensive collection of present programmes and methods for the seamless analysis of surfactants.

Reference:

(1) http://chemistry.about.com/od/howthingswork/f/detergentfaq.htm
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Title Annotation:TESTING
Publication:Finishing
Date:Jul 1, 2008
Words:971
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