A new indirect method for the quantification of total organic iodine (TOI) in environmental waters by inductively coupled plasma with mass spectrometry and liquid chromatography with tandem mass spectrometry

Abstract

The formation of emerging iodinated disinfection by-products (I-DBPs) is associated with iodine sources including organic compounds. Total organic iodine (TOI) was used as a bulk index of organic iodinated compounds because of the difficulty in identifying and quantifying individual organic iodinated compounds in environmental waters. Conventional methods for the direct quantification of TOI require complicated pretreatments, which has promoted many studies to attempt to simplify the quantification of TOI by an indirect measurement. In current indirect methods, TOI is mainly calculated as the differences between the concentration of total iodine (TI) and inorganic iodine ($I^{-}$ and ${{\text{IO}}_3}^{-}$) by liquid chromatography-inductively coupled plasma with mass spectrometry (LC-ICP-MS). However, without accurate identification and discrimination by LC-ICP-MS, possible co-eluting iodinated compounds may be detected as $I^{-}$ and ${{\text{IO}}_3}^{-}$. To measure TOI more accurately, a simple method was developed by ICP-MS and liquid chromatography-tandem mass spectrometry (LC-MSMS). TI was measured by ICP-MS, and the spiked recoveries of tested iodinated compounds showed acceptable accuracy and repeatability in Milli-Q water and environmental waters, respectively. $I^{-}$ and ${{\text{IO}}_3}^{-}$ were first simultaneously measured by LC-MSMS without redox pretreatments. The limits of quantification of $I^{-}$ and ${{\text{IO}}_3}^{-}$ in this method were 0.05 $\mu$g I/L and 0.4 $\mu$g/L (0.3 $\mu$g I/L), respectively. The method is highly sensitive, and the actual concentration of $I^{-}$ and ${{\text{IO}}_3}^{-}$ can be calculated by the spiked recovery. The method was successfully applied by measuring TOI concentration (2.2 to 17 $\mu$g I/L) in various types of environmental waters.