Analysis of unconjugated morphine, codeine, normorphine and morphine as glucuronides in small volumes of plasma from children.

A sensitive method for the analysis of unconjugated morphine, codeine, normorphine and total morphine after hydrolysis of glucuronide conjugates is described. The method was applicable to 50-microliters volumes of plasma. The analytes were converted to heptafluorobutyryl (HFB) derivatives before analysis by gas chromatography-negative ion chemical ionization mass spectrometry. Morphine and codeine were quantified against their [2H3]-isotopomers. Linearity, precision and accuracy were quite acceptable (in the 10(-10)-10(-9) g range), and the absolute limits of detection were < 1 pg.