I know changes in ions per flow rate of saliva & also pancreatic juice... not sweat....
and for saliva, it becomes more isotonic with increased flow (i.e. from an hypotonic state) - reason's is because at faster flow rate.... there's not enough time to re-absorb the ions from the fluid... the only exception is potassium which is about constant. So as flow increases, concentration increases for all of them with the exception of potassium.