what does ppm stand for
The expression 1 ppm means a given solute exists at a concentration of one part per million parts of the solution. These are two common ways to think about what the concentration 1 ppm means: a) it is one-millionth of a gram per gram of sample solution. b) it is one gram of solute per million grams of sample solution. Notice that the more general word 'part' is used above, but 'gram' is used in (a) and (b) just above.