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... RChOH s p e c i e s , f o r m e d by i n t e r a c t i o n of in d iv id u a l r a r e -e a r t h n i t r i l o t r ia c e ta te s p e c i e s a n d K O H a t 2 5 *C a n d a n io n ic s t r e n g th of 0. i , h a v e b e e n d e t e i m i n e d by th e p o t e n t i o m e tr i c m e th o d . 1 . e . , c o m p u te d f r o m th e pH v a lu e s of e q u ilib r iu m m i x t u r e s c o n ta in in g v a ry in g p r o p o r t io n s o f r a r e -e a r t h c o m p le x an d b a s s . T h e r e l a t i o n s h i p of t h e s e c o n s t a n t s to th e io n -e x c h a n g e s e p a r a t i o n o f h a r e e a r t h s a t h ig h pH h a s b e e n d i s c u s s e d . I n tr o d u c tio n F r o m th e pH b u ff e r in g p r o p e r t i e s e n d th e s o lu b ility of r a r e -e a r t h n i t r i l o t r i a c e t a t e (N T A ) c o m p le x e s in b a s e , a a w e ll a s f r o m th e r e s u l t s o f s p r e v io u s i n v e s tig a tio n of th e r e a c t i o n of r a r e -e a r t h H E D T A c o m p le x e s w ith b a s e ,^ i t h a s b e e n a s s u m e d t e n t a t i v e l y th a t v e r y s p a r i n g ly s o lu b le n e u t r a l R C h s p e c i e s c o m b in e w ith an e q u iv a le n t a m o u n t of b a s e to f o r m y .