Gas-liquid chromatographic determination of nicotine and cotinine in plasma.

We report a procedure for determining nicotine and cotinine in plasma. Nicotine is extracted from 1 ml of plasma with diethyl ether, back extracted, and analyzed by gas-liquid chromatography with a nitrogen/phosphorus detector. Nicotine and its internal standard, modaline, had retention times of 1.9 and 2.9 min, respectively. Cotinine is then extracted from the same plasma with dichloromethane and similarly analyzed. Cotinine and its internal standard, lidocaine, had retention times of 3.8 and 4.9 min. Day-to-day reproducibilities (CV) within 14% for nicotine and within 6% for cotinine are attainable for the respective concentration ranges 1-100 microgram/liter and 1-200 microgram/liter. Nornicotine and related alkaloids do not interfere. The sensitivity was such that less than 0.1 microgram (0.62 nmol) of nicotine and 0.1 microgram (0.62 nmol) of nicotine and 0.1 microgram (0.57 nmol) of cotinine could be detected per liter.