The matrix effect was evaluated by comparing the peak area
of neat solution mixture (including Leu, Ile, Val and IS) with the
peak area of the corresponding standard solution spiked in postextracted
blank plasma. Extraction recovery of each analyte was
determined in set of six replicates by comparing the peak areas of
the extracted QC samples with those of the post-extracted blank
plasma spiked with the equivalent nominal concentration of Leu,
Ile, Val or IS.