Jonathan Bruce looks at a technique developed for the analysis of water in hair.
It is not easy to tell a good shampoo from a poor one, especially when advertising concentrates on fragrance and foam rather than cleansing and moisturising ability.
People expect a lot from shampoos and conditioners. Unfortunately, it is not easy to tell a good shampoo from a poor one. Cost, fragrance, and lots of foam is what most people look for in shampoo products. Lather and foam is of little importance, but they often get the most attention.
Foaming occurs when surfactant molecules gather around air instead of oil. The result is millions of tiny bubbles. Obviously, the air bubbles are using the surfactants that should be removing dirt and oil. We have all seen shampoo advertisements showing happy, beautiful people taking showers with their heads heaped high with mounds of lather. These images have taught the public to associate lather with cleansing ability. The truth is, lots of foamy lather only means too much shampoo was used.
Excess foam equals waste. Sebum and other oils quickly destroy foam. Ideally, the head should have just enough lather to lubricate the scalp and hair. This will help the fingers massage the shampoo more effectively into the hair. Fragrances and foaming qualities are not good ways to evaluate shampoos and conditioners. A good way to evaluate the moisturising performance of the shampoo and conditioners is to determine the water content of the hair before and after treatment with the relevant product. A sample of hair is taken from the head prior to treatment. The hair is then washed with the shampoo/conditioner, dried and a further sample is cut from the hair. Fairly large samples of hair were taken.
Historically the analysis of water in hair was not only time consuming but very inaccurate. The sample was typically digested with hot acid and then added to a solvent (typically methanol). This sample solution was then injected into a volumetric Karl Fischer instrument where the moisture content was determined. At every step errors were introduced and subsequently poor relative standard deviations were achieved on the results.
However, with a technique developed by Metrohm, analysis times are shorter and the reproducibility of results is significantly better. Using the 774 oven sample processor in conjunction with the 831KFCoulometer analysis times are typically 35 minutes and RSDs on results are less than 1percent, and more importantly for the hair donor, sample sizes are tiny. The hair is weighed into a vial and the top is sealed (crimped). This sample is then introduced into an oven where the water evolved is titrated in the KF coulometric cell.
The refined methodology of the 774OSP brings decisive advantages. Strictly reproducible analysis conditions for all samples, this is shown by the considerably improved precision of the results. Manual sample preparation is reduced to a minimum, just weigh, crimp and analyse. And there considerable savings in time and money, less reagent costs for example, no more acid and solvent extraction.
There is no contamination of the oven, consequently there is no carryover and memory effects. Improved water release from the sample as the carrier gas does not just pass over the sample but directly through it. Fast analysis times; typically three minutes, and up to 35 samples at a time. Metrohm also has applications where the bound and unbound moisture can be determined separately.
Jonathan Bruce is with Metrohm UK Ltd, Buckingham, UK. www.metrohm.co.uk
