Article by: Kelly Dobos
Raw materials arrive with a certificate of analysis (COA) meant to ensure the product conforms to certain specifications that contribute to end performance and that the material has not degraded or become contaminated. COAs are also very important to review when starting to work with a new or unfamiliar material because parameters covered on the COA can help you understand how the material will function in a formulation and warn you of potential pitfalls. Since the meaning of many of the terms on a certificate of analysis are not obvious, below are some common COA characteristics with information about what they mean when it comes to formulation.
Common Certificate of Analysis Terms
Ash Content — Describes the inorganic content of a material. In ash content analysis the sample is charred and the remaining ash is expressed a percentage of the initial sample weight. Most minerals are converted to oxides, sulfates, phosphates, chlorides or silicates. This information is important when working with ingredients that may be sensitive to metal salts.
Iodine Value — Measures the degree of unstaturation in fats and oils. The lower the iodine value the lower the degree of double bonds and the more solid the material will be. Double bonds may be stronger than single bonds, but they are more reactive, making iodine value a good indicator of stability. Using a material with a higher iodine value may require the addition of an antioxidant and special care in storage.
Peroxide Value — Oxidation during storage and heating causes decomposition and off-odors in fats and oils. Peroxide value analysis measures the concentration of hydroperoxides generated in the first steps of the oxidative process.
Refractive Index (RI) – Measures how much the speed of light is reduced when it travels though a specific medium. A raw material will have a narrowly defined range for RI. RI matching can also be used to create clear formulations.
Penetration — In this test method a needle or cone is pushed into a solid or semi-solid sample with a standard weight. The main determinant of penetration is the hardness of the material. But it can also be telling of the crystalline structure and yield properties. These properties are important when using waxes to stabilize some W/O emulsions or for controlling the properties of lipsticks.
Saponification (Sap) Value — Indicates the mean molecular weight of triglycerides. In the test, the amount of potassium hydroxide needed to saponify (make soap from) 1 gram of a fat or oil is determined. Triglycerides with longer fat chains have a low saponification value because there will be less fat chains to saponify in a 1 gram sample than a sample with many short chain triglvycerides. Sap values are important for making soap and soap-stabilized emulsions. Saponifcation values for NaOH are also available but most commonly reported by KOH, so be sure to check the test method referenced on the COA.
Unsaponifiable Matter Content — While sap value describes fat chain length, unsaponifiable matter content is a measure of the other organic components contained in fats and oils. This may be contaminant like mineral oil or naturally occurring sterols, tocopherols, pigments, etc. This test involves the saponification of a sample followed by dilution and extraction with an organic solvent.
Hydroxyl Value – Triglycerides in fats and oils are subject to hydrolytic rancidity. Hydroxyl value measures the free —OH groups formed by cleavage of fat chains from the glyceride molecule that occur with hydrolysis. The hydroxyl value can be used as an indication of the quality of the material.
Acid Value — Similar to hydroxyl value, acid values measures hydrolytic rancidity by measuring the free fatty acids have been liberated from their ester linkage with a parent glyceride molecule by titration with a base. High hydroxyl and acid value numbers indicated rancidity.
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