Simultaneous determination of nicotine and cotinine in plasma using capillary column gas chromatography with nitrogen-sensitive detection.

A rapid and sensitive method is described for the stimultaneous determination of nicotine and its principal metabolite, cotinine, in plasma. A one-step extraction procedure is employed and the quantitative analyses are performed by capillary column gas chromatography using a thermionic specific detector. Other special measures to avoid contamination from external sources such as atmosphere, solvents and laboratory equipment, which constitutes the major limiting factor of nicotine assay, were also undertaken. The structural analogues of nicotine and cotinine, N-methylanabasine and N-ethylnorcotinine, are used as internal standards. Moreover, a micromethod, which requires only 0.1 ml of plasma and found to be suitable for analysis of cotinine in finger-tip samples of blood, is described. LInearity over the concentration ranges 5-100 ng of nicotine per ml of plasma and 5-500 ng of cotinine per ml of plasma is demonstrated. The precision of the method has been investigated by determining the reproducibility at different levels of nicotine and cotinine within the working ranges, for both 1-ml and 0.1-ml samples of plasma.