Adsorbable organically bound halogens (known as AOX) are the sum of numerous halogenated organic compounds that are adsorbable on activated carbon. Many of these organic halogen compounds and their degradation products pose serious risks to human health and the environment. Therefore, AOX must be monitored to ensure adequate water quality as well as to trace its sources and investigate the efficiency of AOX removal techniques in water treatment processes.

Historically, this sum parameter was determined by microcoulometric titration as per DIN EN ISO 9562 or EPA 1650. However, AOX comprises AOCl, AOBr, and AOI, which cannot be determined individually. The new DIN 38409-59 describes a procedure of adsorption and analysis via combustion ion chromatography (CIC) to determine AOCl, AOBr, AOI, the sum parameter CIC-AOX_(Cl), as well as AOF – a monitoring parameter for per- and polyfluorinated alkyl substances (PFASs), which are of increasing global concern.