19341
Natural product drug discovery programs often rely on the use of silica ( Si ) gel , reversed - phase media , or size - exclusion resins ( e . g . , RP - C ( 18 ) , Sephadex LH - 20 ) for compound purification .
 Chemical: silica; Chemical: Si
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: silica; Chemical: Si