Time-course measurements of caffeine and its metabolites extracted from fingertips after coffee intake: a preliminary study for the detection of drugs from fingerprints

The aim of this study was to determine whether an ingested drug and its metabolites could be detected in the subject's fingerprints. Caffeine (CF) was chosen as the model drug. Three healthy subjects were asked to consume a cup of coffee (ca. 100 mL) containing 80 micro micro mg CF as the total dose, which is the normal amount in one cup of coffee. After washing hands with water to remove external contaminants, each subject pressed the index fingertip to a collecting matrix just before consuming the test cup of coffee, and then again pressed the index fingertip to the collecting matrix after 1, 3, 5, and 7 h. The time curve of the amounts of CF and its metabolites-theobromine (TB), paraxanthine (PX), and theophylline (TP)-in fingerprints and blood was determined using liquid chromatography/tandem mass spectrometry (LC/MS). A filter paper wetted with water (50 mu L) was an efficient collecting matrix for extracting the analytes from the fingertip. With optimized sample preparation and LC/MS conditions, the total operating time, from taking the fingerprints to obtaining the analytical result, was approximately 10 min. The lower limits of quantification for CF, TB, PX, and TP were 0.5, 5, 0.5, and 5 ng/fingerprint, respectively. The amount of CF or PX determined in fingerprints obtained over 7 h after coffee intake was significantly greater than the amount determined in fingerprints taken before drinking coffee. Fingerprints were a more efficient source for drug testing than other biological samples, such as blood and sweat, because the procedures for sampling and extracting the drugs were simpler and took less time. The method could be used to prove drug intake in criminal investigations.