... peak. For LRMS, use masses at m/z 320, 322, and 257 for 2,3,7,8-TCDD and either m/z 328 for Cl 2,3,7,8-TCDD or m/z 332 for C 2,3,7,8-TCDD. For HRMS, use masses at37 13412m/z 319.8965 and 321.8936 ... C,in µg/L.13. Methods, 330.4 (Titrimetric, DPD-FAS) and 330.5 (Spectrophotometric DPD) for Chlorine, Total Residual,” Methods for Chemical Analysis of Water and Wastes,EPA-600/ 4-7 9-0 20, U.S. Environmental ... must resolve 2,3,7,8-TCDD from the other 21TCDD isomers.12.6.2 The masses for native 2,3,7,8-TCDD (LRMS-m/z 320, 322, and 257 and HRMS-m/z 320 and 322) and labeled 2,3,7,8-TCDD (m/z 328 or 332)...