c e u t i s c h I n s t i t u u t , V r i j e U n i v e r s i t e i t Brussel Paardenstraat 67, B-1640 S i n t Genesius Rode Received 29.06.72 -Accepted 29.09.72 SUMMARY Procedures f o r t h e determination of n i t r a t e i n mineral water i n t h e 0,s -5 p.p.m. concentration range with t h e n i t r a t e s e l e c t i v e e l e c t r o d e and U.V. spectrophotometry are compared with a c l a s s i c a l c o l o r i m e t r i c procedure. Because t h e use of a calomel e l e c t r o d e and Hg-Hg2S04 e l e c t r o d e as reference e l e c t r o d e caused short-time f l u c t u a t i o n s , t h e p o t e n t i o m e t r i c determination was c a r r i e d out using a f l u o r i d e s e l e c t i v e e l e c t r o d e as reference e l e c t r o d e a f t e r a d d i t i o n of a f l u o r i d e s p i k e t o t h e s o l u t i o n . The U.V. method proved t o be r a p i d , p r e c i s e and a c c u r a t e . The potentiometric method was a l s o very r a p i d and although it gave acceptable r e s u l t s i n f i v e c a s e s out of s i x it i s i n f e r i o r t o t h e U.V. spectrophotometry i n t h e o t h e r aspects.