ABSTRACT
Organic compounds 3.1 X A D - I resins T h e p r i n c i p l e of adso rp t i on techniques for preconcent ra t ing samples is qui te s imp le . A large v o l u m e of s a m p l e is contacted w i t h o r passed d o w n a c o l u m n of a s o l i d ma te r i a l w h i c h r emoves organic ma t e r i a l f r o m the wate r in to the s o l i d . M a n y m e c h a n i s m s can be respons ib le for this; a d s o r p t i o n p h e n o m e n o n is one. I n the next stage, the organics a n d i n a l i m i t e d n u m b e r of cases o rganometa l l i c c o m p o u n d s are r e m o v e d f r o m the s o l i d in to a v o l u m e of a so lvent o r a c h e m i c a l reagent w h i c h is r e l a t ive ly l o w c o m p a r e d to the o r i g i n a l v o l u m e of s amp le taken, a n d subsequen t ly e x a m i n e d b y gas c h r o m a t o g r a p h y o r h i g h p e r f o r m a n c e l i q u i d c h r o m a t o g r a p h y ei ther of w h i c h m i g h t be c o u p l e d to a mass spectrometer. A l t e rna t i ve ly , the adsorbent m i g h t be hea ted to release the organics w h i c h are then s w e p t i n to a c ryogen ic t rap for subsequent ana lys i s b y the a forement ioned ch roma tog raph ic techniques or s w e p t d i rec t ly i n to a gas ch roma tog raph . In favourable c i rcumstances preconcent ra t ion factors o f u p to 10 4 o r e v e n h ighe r are c o m m o n l y ach ieved b y these techniques . N a t u r a l l y , the types of resins f r o m w h i c h preconcentra ted substances can be s u b s e q u e n t l y re leased e i the r b y s o l v e n t e x t r a c t i o n or t h e r m a l deso rp t ion m u s t themselves h a v e n o polar i ty . O n l y the n o n - p o l a r resins are d i scussed i n this chapter. P o l a r (ie i o n exchange) resins are d i s cus sed i n Chap te r s 4 a n d 5). N o n - p o l a r resins, as o p p o s e d to p o l a r resins, operate b y f o r m i n g v a r i o u s k i n d s of loose p h y s i c a l b o n d s (rather t h a n c h e m i c a l bonds ) w i t h the adsorbed substance, or, i n the case of larger adso rbed molecu les , m a y operate o n the p r i n c i p l e of ac t ing as microf i l te rs , ie the pore sizes i n the res in are of m o l e c u l a r d imens ions .
