■Add the marker substance first Before solid-phase extraction, add PFOS or PFOA with some of the carbon replaced by 13C to the water sample to correct the recovery rate during the operation. ■Should branched forms also be counted? PFOS and PFOA have straight-chain linear forms and branched isomers. In tap water testing, the concentration is determined by combining the peak areas of the linear and branched isomers. In the measurement methods for rivers and groundwater, it is also acceptable to quantify branched isomers using the calibration curve of the linear form. ■Substances that produce signals similar to PFOS! Deoxycholic acids found in biological samples and urine produce ions with the same combination as PFOS. Therefore, in samples from downstream wastewater treatment plants, it is necessary to compare the intensity ratio of the two types of ions with that of the standard solution to confirm whether it is truly PFOS. ■Is the measurement method the same for tap water and rivers? The method for testing compared to the standards for tap water has been added to the national notification and will be applied from April 2026. The measurement methods for rivers and groundwater are established separately. Even for the same substance, it is measured using the method appropriate for the purpose.

■Is it okay to use a glass water sampling container? PFOS and PFOA are known to easily adsorb to glass and can leach from equipment. Therefore, it is advisable to avoid glass containers as much as possible. Also, avoid buckets with fluoropolymer coatings and thoroughly wash them with methanol before use. ■What should you decide before making a request? 1. Purpose: Are you comparing to drinking water standards or conducting voluntary checks? 2. Target: Are you only testing for PFOS and PFOA, or will you include other PFAS as well? 3. Lower limit: What concentration level is sufficient compared to the standard value? 4. Sampling: Confirm the container and sampling method with the testing organization in advance. ■Where should you request water testing? According to the Water Supply Act, water suppliers must establish testing facilities, but they are not required to do so if they outsource testing to local government agencies or nationally registered organizations. ■Consider the implications of the results After reviewing the test results, you will need to think about necessary measures and subsequent actions. Our company offers consultations on water treatment equipment such as activated carbon and filtration systems. Please feel free to reach out to us first.