A Ring Trial Test of Nicotine Uptake Determinations by Multiple Laboratories

摘要

Total nicotine uptake by smokers is best determined by measuring nicotine and its major metabolites (usually five) in 24-h urine samples. Most methods are based on LC-MS/MS using either indirect or direct determination of conjugated metabolites. Of additional interest is the primary nicotine metabolite cotinine in saliva since it is also related to total nicotine uptake. Nicotine uptake is a part of understanding smoking behavior and it is important that laboratories generate comparable data. CORESTA, an association to promote international cooperation in research related to tobacco, recently coordinated a ring trial test among several laboratories for performance testing of nicotine uptake determinations in urine and saliva. The results are presented here. Uniform sets of urine and saliva samples were prepared and shipped to 10 participating labs. Each set had 42 samples of each matrix (urine and saliva). Within each set were embedded calibration standards (seven in triplicate) prepared by adding known amounts of each analyte to a nonsmoker matrix; the remaining samples (seven in triplicate) were authentic samples from smokers. Samples were randomized and coded so participants would not know which samples were calibration standards and which were authentic samples. Participating labs analyzed all samples as unknowns using their own calibration standards and analytical methods and returned the data, including raw area counts and response equations (linear, quadratic, or power function), to the coordinator. Reported data were recalculated using the embedded calibration curve.