SW-846, Method 0050 is an isokinetic sampling train for the determination of HCl/Cl2 from hazardous waste incinerators and municipal waste combustors, especially suited for those sources with wet scrubbers emissions of acid particulate matter (e.g., HCl dissolved in water droplets. As you recall, Method 0051 was designed for those stacks which were relatively dry, particulate free. Must use Method 0050 at sources controlled by wet scrubbers that emit acid particulate matter and have water droplets.
Federal Reference Method (FRM) 26 is the same as SW-846, Method 0051 except FRM 26 is for hydrogen chloride (HCl) emissions only (whereas Method 0051 can quantitate Cl2 also). Finally, FRM 26A is different from SW-846, Method 0050 (both isokinetic), in that FRM 26A is applicable for determining emissions of hydrogen halides (HX) [specifically HCl, HBr, and HF], and halogens (X2) [specifically Cl2 and Br2]. Method 0050 only quantitates HCl and Cl2.