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.

Have more certificate of analysis questions?  Leave a comment below.


  1. Avatar


    Thanks for such a precious article! I’m a formulation newbie who just step into this industry. I hope that you could answer my question below for my better understanding:
    1. Regarding the ash value, is that mean that the higher the ash value, the higher chance for it to destroy salt sensitive system, for example, carbomer system?
    2. Regarding the peroxide value, if that means that the higher the peroxide value, the more unsaturation is the fats/oils an hence the easier the fats/oils got rancid?
    3. Regarding the penetration, it is mentioned that the penetration is important when using waxes to stabilize some W/O emulsions or for controlling the properties of lipsticks. Can I have more explantion of it. For example, how does it work and what do we choose the right penetration?

    I hope that my questions aren’t silly. Thank you so much in advance.

    1. Kelly Dobos
      Kelly Dobos

      Hi Venus
      Here are some answers to your questions. Hope this helps.
      1. A higher ash value could impact stability in such systems so it’s important to monitor stability closely. But it’s important to note ash value is measure after a material is completely combusted.
      2. Iodine value is a measures the level of unsaturation. Peroxide value measures byproducts of the oxidation process, so the degree to which a material has already oxidized.
      3. Typically, a lipstick needs a blend of waxes that are hard enough to give the stick stability so that it doesn’t break during application but soft enough to apply smoothly.

  2. Avatar

    Hi Kelly. Thanks for the article. It’s really useful.
    When trying to qualify an alternate raw material supplier and notice some differences in CoA specifications from your current RM spec, how do you define major specifications which can not be compromised and minor differences which can be overlooked?

  3. Avatar

    Hi Perry,
    What kinds of information is included in a COA of a bulk (not raw materials) ?

    1. Kelly

      Hello Jolie
      This is Kelly, the author of this particular post. It depends on the type of formulation. You will have to determine what are important specifications related to safety, stability, and performance that you want to measure for each lot produced. One example, is microbiological specifications as each lot of product should be free from contamination. But in some cases like solvent based nail polish and micro specification would not be necessary as high levels of solvents used prevent the growth of microorganisms.

  4. Pingback:Natural Oils in Cosmetics and Personal Care – Chemists Corner

  5. Avatar

    Lets say I want to package a 100 kits. The kit has two components that go into it. Component “a” we have 100 pieces of the sam lot but componet “b” we have 75 pieces of one lot and 25 pieces of another lot. Currently we package two different lots one lot of 75 pieces and a 2nd lot of 25 pieces and do a coa for both lots. Is it possible to package one lot of 100 pieces. In this lot 75 of the kits would have 1 lot of component “b” and the other 25 pieces would have a differnet lot of component “b” and only do one coa for the lot of 100?

    1. Avatar
      Perry Romanowski

      I have no idea but I imagine there is not some specific rule and it would just be up to the opinion of your regulatory people.

  6. Avatar
    satyanarayana murthy

    sir, this is very useful for us for how to prepare C O A , can i get C O A for soap oil

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