The manufacture of ingredients such as preservatives, vitamins, and sunscreens used in cosmetic and personal care products must meet stringent safety and quality standards (link to U.S. FDA page). The quality control of cosmetics is important to ensure the safety and efficacy of products and its raw-materials. With the start of the summer season coming up and the need to stock up on sunscreen lotions and sprays for a daughter with sensitive skin, I decided to get educated on the subject having learned from a post my colleague, Sonya Pelia, wrote a while back on benzalkonium chloride--an antimicrobial agent in sunscreen--that has been associated with allergic reactions to the skin, eyes, and respiratory systems.
Physical & Chemical Sunscreens
After a little digging, I learned there are two general types of sunscreens, Physical and Chemical sunscreens. Physical sun screens reflect and scatter the suns UV rays while chemical filters operate by absorbing UV rays. Physical sunscreens include titanium dioxide that protects against UVB rays, and a portion (but not all) of UVA rays. Chemical filters offer more coverage by absorbing both UVA and UVB rays, but the range of protection depends on the particular active ingredient and its stability.
Physical sunscreens tend to be better tolerated by most skin types while Chemical filters tend to be more irritating to skin and can cause allergic reactions. There are a host of chemical additive ingredients used in sunscreens including Octylcrylene, Avobenzone, Octinoxate, Octisalate, Oxybenzone, Homosalate, and other aromatic compounds, some of which have their own side effects including environmental concerns (downloadable PDF of UHPLC method for analysis).
Is that Boric Acid or Borate Necessary in Your Sunscreen?
But, not all ingredients in sunscreens are designed to block UV rays. I also learned that additional additives present in sunscreen (and cosmetics in general) are boric acid and borates, used as preservatives, antibacterial agents, and to adjust the thickness of a lotion. The downside, however, is if inhaled or absorbed through skin cuts, boric acid and borates can cause intoxication.
As a result, the amount of boric acid and borates is strictly regulated with the concentration reported as a weight percent with maximum limits depending on the cosmetic product. In fact, cosmetics for children under three years are prohibited from containing these additives, demonstrating the need for detection method with a high level of sensitivity.
The standard used in Europe and China to achieve appropriate sensitivity limits is a spectrometry method using azomethine-H as a colorimetric reagent. The amount of boric acid and borates is strictly regulated with the concentration reported as a weight percent and a limit of detection as low as 0.1%. But did you know, the method has a method detection limit (MDL) of 47 µg/L and is unable to meet the strict requirements needed for detecting boric acid in cosmetics? (By the way, Method of Detection Limit (MDL) is the minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero, and is determined from analysis of a sample in a given matrix containing the analyte.)
Ion Chromatography Analysis of Boric Acid in Cosmetics
To fill the need for more sensitive detection, an ion chromatography method used in the determination of boric acid in water samples was applied to th... (downloadable PDF of method). To test the efficacy of the method in cosmetics, analysis was performed on ten cosmetic samples (two talcum powders, three creams, and five liquids). A calibration standard of boric acid at eight concentrations was used to quantify boric acid in the cosmetics samples. Results provided a measured MDL for boric acid of 15 µg/L, an improvement in sensitivity over the spectrometry method of 47 µg/L by a factor of 3..
Analysis was performed on a Thermo Scientific Dionex ICS 2100 Ion Chromatography system with suppressed conductivity detection and a borate ion chromatography column (Thermo Scientific Dionex IonPac ICE-Borate column) using a methanesulfonic acid eluent.
Learning about cosmetics, sunscreens, and ingredients shows that it’s not just about analyzing an analyte of interest using an approved method, but selecting a method and technique that provides the necessary sensitivity to provide accurate measurements.
Learn more by visiting our Consumer Products web pages where you will find more application notes, videos, and more. We are constantly adding new content to these pages, so please check back often.
I would be interested in hearing from you if you are working on the analysis of ingredients in cosmetic and personal care products.