[en] Neutron activation analysis has been used to monitor the loss of arsenic, as dimethylarsinic acid, (CH₃)₂AsOOH, or as sodium arsenate (Na₂HAsO₄.7H₂O), antimony (as potassium antimony, tartrate, KSbC₄O₇.1/2H₂O) and bromine (as bromide ion) during lyophilization of acidified and neutral aqueous synthetic and environmental samples. Losses of Sb and As ranged from zero to 60%, while losses of bromine were constant (at 91%) in acidic solutions. The variable losses of As and Sb were due solely to the presence of and partial decomposition of the (CH₃)₂AsOOH. Electrochemical oxidation of Br^- to Br₂ is responsible for the high losses of bromine. In addition losses of mercury (as methylmercuric chloride) were 1O0% in both acidic and neutral aqueous synthetic samples during lyophilization. (author)