Isolation of basic drugs from plasma using solid-phase extraction with a cyanopropyl-bonded phase.

The use of a CN sorbent for the isolation of basic compounds from plasma is described. Adsorption from water and plasma was investigated for a test set of 30 basic drugs. It was found that compounds with a carbon chain length greater than or equal to 11 are totally retained and that the competitive effect of the matrix on the adsorption is minimal. Methanol-phosphate buffer (pH 3, mu = 0.05) (50:50) yielded good recoveries for more polar compounds; apolar basic drugs can be efficiently eluted using methanol containing 0.1% propylamine. Water up to 3 ml can be used for the washing step. This approach was applied to the determination of eight drugs in plasma at therapeutic levels. The absolute recoveries (n = 6) obtained were 98.8 +/- 7.3% for papaverine, 82.3 +/- 3.9% for practolol, 83.4 +/- 2.6% for metoclopramide, 87.3 +/- 5.8% for imipramine, 82.8 +/- 3.3% for procaine, 82.7 +/- 4.6% for morphine, 87.5 +/- 7.2% for propranolol and 90.4 +/- 6.2% for yohimbine.