[schedler]

CHEMICAL ANALYSIS OF GROUNDWATER:
For the determination of CHLORIDE I use the argentometric/chromate method of Mohr.
Question:  Does the presence of sulfate (precipitation of silver sulfate) affect the results, giving a too high chloride content?  If so, should I first analyse for sulfate, then subtract the equivalent from the chloride result?
Thanks

[Borek]

Perhaps you can precipitate sulfates adding barium nitrate?

[Alberto_Kravina]

Yes! You can analyze the sulfates by precipitation with BaCl₂, or Barium nitrate, it's the same thing.
If you want to do a quantitative analysis you can determine the grams/L (or moles/L) of sulfate by gravimetric.

[skyaintsnow]

Adding barium nitrate is a better idea, since by adding barium chloride you are importing chloride ions (one more step in calculation, one more source of uncertainty)