1.1 ,This guide applies to ultrapure water that is thought to contain low ppt (parts-per-trillion, weight/weight) levels of anionic contaminants (for example, bromide, chloride, fluoride, nitrate, nitrite, phosphate, and sulfate). To minimize carry-over problems between analyses, it is best to limit the concentration of any one contaminant to approximately 200 ppt (although this limit is only an approximation and may vary, depending on the user’,s application).