Extraction-Free, Direct Determination of Caffeine in Microliter Volumes of Beverages by Thermal Desorption-Gas Chromatography Mass Spectrometry

An extraction-free method requiring microliter (μL) volumes has been developed for the determination of caffeine in beverages. Using a pyrolysis-gas chromatography mass spectrometry system, the conditions required for the direct thermal desorption-gas chromatography mass spectrometry (TD-GC/MS) determination of caffeine were optimised. A 5？μL aliquot was introduced to the thermal desorption unit, dried, and thermally desorbed to the GC/MS. The response was linear over the range 10 to 500？μg/mL (R2？=？0.996). The theoretical limit of detection (3 σ) was 0.456？μg/mL. No interferences were recorded from endogenous beverage components or from commonly occurring drugs, such as nicotine, ibuprofen, and paracetamol. Replicate caffeine determinations on fortified latte style white coffee and Pepsi Max？ gave mean recoveries of 93.4% (%CV？=？4.1%) and 95.0% (%CV？=？0.98%), respectively. Good agreement was also obtained with the stated values of caffeine for an energy drink and for Coca-Cola？. These data suggest that the method holds promise for the determination of caffeine in such samples