Identification and Quantification of a Predicted Iodinated Disinfection Byproduct in Chlorinated Waters–Dichloroiodoacetic Acid

Abstract Identifying unknown iodinated disinfection byproducts (I-DBPs) is critical for drinking water safety because of their high toxicity. This study identified and quantified a previously predicted yet analytically challenging I-DBP, dichloroiodoacetic acid (DCIAA), which was overlooked during electrospray ionization because of in-source fragmentation. The molecular formula and structure of DCIAA were confirmed by using high-resolution mass spectrometry full-scan analysis and product ion scan characterization of the chlorinated products of the organic iodine-containing precursors. After isolating and purifying DCIAA generated through the chlorination of 2-iodophenol at pH 8.0, the compound was quantified using inductively coupled plasma mass spectrometry and subsequently used as a standard. DCIAA was stored in a 10 mM phosphate buffer solution (pH 7.0) and remained stable under simulated drinking water distribution system conditions. The quantification method was developed using multiple reaction monitoring with optimized precursor/product ion transitions at m/z 208.8/126.9. Weak anion-exchange cartridges exhibited optimal recovery for the solid-phase extraction of DCIAA. DCIAA concentrations ranged from undetectable to 38.8 ng/L in real tap water samples in Japan and from 129.8 to 463.1 ng/L in chlorinated raw water prepared in the laboratory, revealing the occurrence and importance of DCIAA in drinking water.