... Chlorosub-stitution in positions 2, 3, 7, and 8 gives 2,3,7 ,8- tetrachlorodibenzo- p -dioxin(2,3,7 ,8- TCDD), CAS [1746-01-6], occurring in trace amount in chlorophenoxy-acid herbicide, 2,4,5-T. 2,3,7 ,8- TCDD ... the characteristicm/z for 2,3,7 ,8- TCDD are 319 .89 65 and 321 .89 36. The m/z for the corresponding 37 C l4 - and 13C 12 -isomers in HRMS are 327 .88 47 and 331.9367, respectively.The ... may be adhering to it. It is dried in an oven for several hours at 105°C, cooled in a desiccator, and weighed.Heating, cooling, and weighing is repeated until a constant weight is obtained.Alternately,...