Chromatographic micro-procedure for trace determination of phenobarbital in blood serum

Volumes of 100 μl of serum were sufficient for the determination of therapeutic levels of phenobarbital. The isolation procedure was performed using a column method with a hydrophobic adsorbent, graphitized carbon black (Carbopack B). With this method the quantitative (98.1%) recovery of phenobarbital was measured. By suitable choice of experimental conditions, a highly selective purification of the drug can be obtained, thus eliminating various sources of error during quantitation due to the presence in the final samples of endogenous compounds. For the quantitation procedure, another type of graphitized carbon black (Carbopack C) suitably modified was used for gas chromatography. Calibration curves showed no chemisorption effect along the column even on injecting 5 ng of phenobarbital. Some practical aspects of the procedure for improving the reliability of the results are discussed.