APPLIED SCIENCE LABORATORIES, INC

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HELP STAMP O U T C R E E P I N G IMPURITIES! A r e y o u using TLC and c o l u m n c h r o m a t o g r a p h y f o r analysis and p r e p w o r k , or are y o u just p u r i f y i n g y o u r silica gel p o w d e r s ? Most commercially available silica gels (including TLC and c o l u m n p o w d e r s ) contain i m p u r i t i e s w h i c h become q u i t e e v i d e n t if one of the f o l l o w i n g tests is m a d e : 1. Prepare a TLC p l a t e , spray it w i t h sulphuric acid and char. If the plate is g r a y , or has many small black specks, this is due to the presence of impurities. 2. In normal usage of TLC plates can y o u readily see the solvent f r o n t ? If so, this indicates there are i m p u r i t i e s present. 3. Do a Soxhlet e x t r a c t i o n o n any of the commercial TLC p o w d e r or c o l u m n silica gels. Take a p o r t i o n of the extract and inject it into a gas chromat o g r a p h and SEE THE IMPURITIES. N o w , if all these impurities are present in your p o w d e r s , can y o u see the p r o b lems that m i g h t result if y o u are t r y i n g to p u r i f y or analyze a sample? O u r silica gels are acid and base w a s h e d and f u r t h e r cleaned by extensive solvent e x t r a c t i o n . WE GUARANTEE that they are the cleanest available. Our ADSORBOSIL p o w d e r s w i l l p r o v i d e the same t y p e of separations as those r e p o r t e d by Stahl, " P h a r m a z i e , " 1 1 , 6 3 3 (1956), whereas some other commercially available p o w d e r s w i l l not.

APPLIED SCIENCE LABORATORIES, INC. Post Office Box 4 4 0 • State College, Penna. 1 6 8 0 1 Telephone (Area 814) 2 3 8 - 2 4 0 6 West Coast Office: Unit M • 5140 W . 106th St. • Inglewood, Calif. Circle No. 5 on Readers' Service Card

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ANALYTICAL CHEMISTRY