This part of ISO 15181 specifies the apparatus and analytical method for determining the amount of tolylfluanid and dichlofluanid that has been released from an antifouling paint into artificial seawater in accordance with the procedure given in ISO 15181-1. Tolylfluanid and dichlofluanid are unstable in the marine environment and degrade to form dimethyltolylsulfamide (DMST) and dimethylphenylsulfamide (DMSA), respectively. This part of ISO 15181 specifies a method for converting the released species into these degradation products, quantifying their concentration in the treated artificial seawater samples, and gives the final calculation for the release rate of tolylfluanid and dichlofluanid under the specified laboratory conditions. This part of ISO 15181 is designed to allow the concurrent determination of tolylfluanid, dichlofluanid and other biocides that can be released by a given antifouling paint (for example, copper) through the analysis of separate sub-samples of an artificial seawater extract generated in accordance with ISO 15181-1. When used in conjunction with ISO 15181-1, the practical limits for quantifying release rates by this method are from 1,3 µg·cm−2·d−1 to 500 µg·cm−2·d−1. The quantitation of release rates lower than this range will require the use of an analytical method with a lower limit of quantitation for tolylfluanid, dichlofluanid, or both (as appropriate) in artificial seawater than that specified in Clause 3 and in 5.1.