Although chelating agents are used in small quantities, a little goes a long way in keeping a formula stable. They do this by binding metallic ions in water or other chemicals that might adversely affect the color, quality or appearance of the formula. Metal ions such as calcium, iron, magnesium and copper are inactivated by the chelating agent to form a metal-chelate complex. The negatively charged chelate reacts with the positively charged metal to form the metal chelate plus excess acidity.
In addition to softening water, chelates can also function as preservatives in two different ways. First, they act as antioxidants to prevent rancidity of fats and oils (especially if unsaturated) by complexing with trace amounts of metal ions such as copper, magnesium, and iron which can catalyze the oxidation of fats. Second, in combination with other commonly used preservatives such as the parabens, imidazolidinyl urea and quaternary ammonium compounds, they can function as an antimicrobial agent.
The most common chelate used in the cosmetic industry is ethylenediaminetetraacetic acid (EDTA) and its derivatives. EDTA has poor water solubility (only 0.05%) so its sodium salts, being more water soluble, are mostly used. It is believed that EDTA is able to increase the permeability of the cell wall of gram negative bacteria which enables it and other antimicrobials with it to enter the interior of the cell and destroy it.
Kinetik Technologies, Hazlet, NJ, offers a different chelate called Dermofeel PA-3 (INCI: Sodium phytate). This product is manufactured by Dr. Straetmans, a German company located in Hamburg. It is a clear, yellow liquid that contains 11.2-12.2% phosphate. It is soluble in water, glycerol and alcohol, is stable for at least three years, and is biodegradable. According to the manufacturer, Dermofeel PA-3 performs better than EDTA at sequestering metal ions in formulations.
Phytic acid (C6H18O24P6) or inositol hexakisphosphate from which the sodium salt is formed, is the principal storage form of phosphorus in many plant tissues, especially bran and seeds (Dermofeel PA-3 is extracted from rice bran). Phytic acid has therapeutic uses as its mineral binding properties may also prevent colon cancer by reducing oxidative stress in the lumen of the intestinal tract. It also has been shown that a low consumption of phytic acid is a risk factor for osteoporosis.
In cosmetic formulations, Dermofeel PA-3 can be used in pH ranges of 3-10, and the use level is 0.05-0.2%.
Below is a formula illustrating the use of Dermofeel. Most of the ingredients are available from Kinetik.
Intense Healing Lotion
Waterqs to 100
Caprylyl glycol, glycerin,0.25
Glyceryl stearate citrate,5.00
White beeswax NF0.50
Octyldodecanol, echium 3.00
plantagineum seed oil,
seed oil, unsaponifiables
serrulata (saw palmetto)
Sodium hydroxide 25%0.34-7.0
Procedure: Add Phase A ingredients to water in batch tank with high speed mixing and heat to 70°C.Mix Phase B in separate container, heat to 70°C. and add to batch tank. Remove heat and add sodium hydroxide. Begin force cooling while mixing with homogenizer. Cool to 50°C and add fragrance if desired.
Harvey Fishman has a consulting firm located at 34 Chicasaw Drive, Oakland, NJ 07436, firstname.lastname@example.org, specializing in cosmetic formulations and new product ideas, offering tested finished products. He has more than 30 years of experience and has been director of research at Bonat, Nestlé LeMur and Turner Hall. He welcomes descriptive literature from suppliers and bench chemists and others in the field.