Skip to Primary Navigation Skip to Site Navigation Skip to Main Content All Site Map

Tech Talk: Measuring Disinfectant/Sanitizer Concentration

June 1, 2012

Disinfectants and sanitizers are chemical substances or mixtures of substances and are registered through the US EPA with efficacy (kill) claims for microorganisms at a certain concentration of chemical active(s). The chemical identity and concentration of each active can be found on the product or EPA master label, which correlates to the EPA Registration Number for that product. Many of these products are sold as concentrates, which are then diluted with water at the point of use either manually or using a dilution system (sometimes called a dispenser or proportioner). Ready-toUse (RTU) solutions may then be stored and applied in a variety of ways, and a number of factors could cause the chemical active concentration in these solutions to vary from the intended concentration indicated in the EPA Registration. Dyes are often added to these products and can be a rough indicator of concentration, but dye color can be affected by factors such as water hardness, pH, and temperature, so its usefulness is limited for verification of disinfectant or sanitizer concentration. Measuring this disinfectant or sanitizer active concentration "in the field" after dilution or during product use can be a valuable technique for verifying the accuracy of your dilution or for determining if steps in your process are adversely affecting disinfectant or sanitizer concentration, but it is important to understand the application and limitations of your measurement technique to gain the maximum benefit from your measurement efforts.

Evaluating Measurement Methods

Determining the chemical identity of your disinfectant and sanitizer active ingredients is the first step in evaluating potential measurement methods. The most commonly used actives are quaternary ammonium chloride compounds (quats), but other actives such as chlorine bleach (sodium hypochlorite), phenolics, or peracetic acid and/or hydrogen peroxide products can also be found. There are a variety of products for measuring quats, peroxide, or bleach (as chlorine) in the field, but there may be no field-use products for some of the other active ingredients. You may need to consult with an analytical laboratory about potential testing of actives where no field measurement method exists or if you need more accurate results than can be obtained using field methods.

Starting Your Measurement Program

The remainder of this Tech Talk will focus on measuring quat or bleach actives in disinfectants and sanitizers with field-use methods, though that does not imply that only quat or bleach products are prone to problems that may affect their concentration. Regulators and inspectors who may review the results of these measurements should be asked to keep in mind that those records reflect efforts to evaluate and improve the disinfection and sanitization process by taking advantage of the ability to easily measure certain actives in the field. Therefore, it would be unfortunate to penalize the user for a low quat result, for example, while no field measurement results may be available for other active ingredients to help with process improvements.

After identifying the chemical identity of your active ingredient(s), determine what the RTU concentration should be, based on the EPA Registration for the product. It is best to obtain the EPAapproved RTU ppm value for the disinfectant active from the product manufacturer, but the following formula can be used to approximate the parts per million (ppm) value from the ingredient information on a product label if you are not able to obtain it from your supplier.

Test Strips vs. Titration Kits

The two main field measurement methods available for quats and chlorine bleach actives in disinfectants and sanitizers are either test strips or titration kits. Test strips usually have individual segments on them that will change color in response to a certain level of the active chemical to be measured and will cover a range of concentrations typical to disinfectants and sanitizers in increments of 10 to 500 ppm. They are often easier to use than titration kits, but the color variation between concentrations can be subtle, and the concentration increments can be too large (such as several hundred ppm) to make them useful in discerning small differences in concentration that might be valuable in process improvement efforts. When using test strips, it is important to choose a strip that covers the expected concentration in a range above and below that target with the smallest increments possible.

Titration kits can be used to obtain a more refined value than test strips, though even those results will have a margin of error. There are several suppliers of these field measurement methods, and manufacturer instructions for use and information on how to interpret results should always be followed. The website for one commonly used supplier (LaMotte) is, and their #3042 Titration Kit covers the range of quat concentration found in many disinfectant products using that active ingredient. However, as an example of the margin of error with field measurement previously mentioned, a range of plus or minus 50 ppm can be expected for this particular kit. Additionally, a Gage R&R statistical study performed by 3M to assess the reproducibility and repeatability of the LaMotte #3042 kit confirmed these results. From a practical perspective, this means that when the ""real"" level of quat is, for example, 710 ppm, a spread of 660 to 760 ppm can be reasonably expected. It is important to obtain this margin of error information from the manufacturer of any field measurement kit so that results can be interpreted appropriately.


Measuring the concentration of your disinfectant or sanitizer solution can be a useful way to help ensure the effectiveness of your process. Test strips and titration kits are the two primary field measurement methods used, but carefully following manufacturer directions and understanding the limitations of any method is important when interpreting results. It is important to use a method intended for the type of active and expected concentration in your disinfectant or sanitizer, but other aspects of your measurement program (such as how often to test) will depend on a number of variables, including the reliability of your products and the consistency of your processes.that results can be interpreted appropriately.

   Return to: