22897
In many cases , liquid chromatography - tandem mass spectrometry ( LC - MS / MS ) provides identical MS / MS spectra among isomeric hydroxylated metabolites , and therefore , it alone cannot unequivocally identify the exact position ( s ) of hydroxylation .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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