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3 . To determine the plasma levels of risperidone and 9 - hydroxyrisperidone in rats , a HPLC method was developed using a liquid - liquid acid back extraction .
 Chemical: risperidone; Chemical: 9 - hydroxyrisperidone
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: risperidone; Chemical: 9 - hydroxyrisperidone