Analysis of Disinfectant Quaternary Ammonium Salts.

Description :
Surface acting agents, commonly known as surfactants, are compounds that serve a variety of roles in many applications. One of their primary functions is to reduce tension at the surface or interface between two differing phases or substances. Due to this unique property, a multitude of industries and applications utilize surfactants as detergents, dispersants, and bactericides as well as foaming, wetting, and antistatic agents. Surfactants display these tension-reducing properties because they may contain one or more amphiphilic groups; compounds that possess amphiphilic groups exhibit an affinity for both polar and non polar substances. Surfactants are generally categorized as anionic, nonionic, cationic, and amphoteric. These categories describe the nature by which each compound disassociates in an aqueous solution and which ion, if any, carries the amphiphilic group.Quaternary ammonium salts are a commonly used cationic surfactant. Cationic surfactants contain a positively charged ion, or cation, that carries the amphiphilic group, allowing them to adsorb negatively charged substrates. Quaternary ammonium salts, specifically, are comprised of a quaternary ammonium cation group, commonly known as a quat; the quats are combined with some anion group, typically a chloride or other halide ion. Due to the aforementioned characteristics, these salts frequently serve as the active ingredient in antimicrobial and disinfectant products.

Application :
A manufacturer of disinfectant wipes was looking to determine the percentage of active ingredients, by weight, in their raw material disinfectant solutions and finished cleaning products. Understanding the quat content of their materials was important for quality control and reporting purposes. As part of the manufacturing process, the wipe product was first soaked in a solution of quaternary ammonium compound, alcohol, and water. The roll of wipe product was then sealed, packaged, and stored. For this application, Hanna Instruments recommended the HI902C Automatic Titration System with the HI4113 Nitrate Combination Ion Selective Electrode (ISE). The nitrate ion selective electrode is approved, along with surfactant electrodes, for the analysis of disinfectant quaternary ammonium compounds per Standard Test Method ASTM D5806. In this method, a cationic compound, such as quaternary ammonium salt, is titrated potentiometrically in an aqueous medium with a standard solution of sodium lauryl sulfate; the nitrate ISE is used as the indicating electrode. A complex is formed between the disinfectant quaternary ammonium compound and sodium lauryl sulfate, which is an anionic surfactant. The complex that is formed then precipitates out of solution and the nitrate ISE responds to the change in potential with a well-defined inflection point. The customer was pleased with the low cost at which Hanna Instruments could accommodate their needs as well as the simplicity of the device when performing the analysis. Because they were beginning to build out their laboratory and quality control area, the manufacturer valued the potential for the titrator to accommodate future methods and the versatility for it to also perform as a benchtop pH meter. Most of all, the customer appreciated the service, support, and commitment received by Hanna Instruments as they developed and implemented new quality control procedures.