interferences: see 2540A.2 and 2540B .1 highly mineralize waters with a considerable calcium, magnesium,chloride, and /or sulfate content may be hygroscopic and require prolonged drying. proper desiccation, and rapid weighing. samples high in bicarbonate require careful and possibly prolonged drying at 180 c insure complete conversion of bicarbonate to carbonate. because excessive residue in the dish may form a water-trapping crust, limit sample to no more than 200 mg residue.