Buyuktuncel, Ebru2024-08-042024-08-0420100003-27191532-236Xhttps://doi.org/10.1080/00032711003731357https://hdl.handle.net/11616/95200A reversed-phase high performance liquid chromatographic method was improved for the simultaneous determination of theobromine, paraxanthine, theophylline, and caffeine in urine. The method includes a liquid-liquid extraction at alkaline pH with ethylacetate. The 7-(2,3-dihidroxypropyl) theophylline was used as an internal standard (ISTD). The separation was achieved on a C18 column using 14:86 methanol:buffer (25mM KH2PO4 adjusted to pH 4 with ortho-phosphoric acid) solution as mobile phase under isocratic conditions at a flow rate 1mLmin-1. An ultraviolet absorption at 274nm was monitored. In these conditions, the LOD was 0.03gmL-1 for theobromine, 0.02gmL-1 for paraxanthine, 0.04gmL-1 for theophylline, and 0.08gmL-1 for caffeine. The method has been applied to urine samples.eninfo:eu-repo/semantics/closedAccessCaffeineHuman urineParaxanthineRP-HPLCDADTheobromineTheophyllineArticle43162518252410.1080/000327110037313572-s2.0-78649723318Q3WOS:000284890400006Q4