Determination of warfarin in waters and human plasma by solid-phase room-temperature transmitted phosphorescence

A new method for the determination of warfarin in waters and human plasma using solid-phase room-temperature phosphorescence is proposed. The sample was spotted on Whatman No. 4 filter paper, together with iodide and NaOH solutions, after which it was dried and its transmitted phosphorescence intensity measured at 467 nm using two quartz plates to avoid the quenching effect produced by oxygen. The applicable concentration range went from 0.3 to 4.0 mg. L-1, and the detection and quantification limits were 0.08 and 0.28 mg. L-1 respectively. The precision of the method, as a relative standard deviation, was 2.3%. The method was applied in the determination of warfarin in human plasma and different types of water. The interferences produced by the albumin of the human plasma were eliminated by the addition of Na2SO4 saturated solution. Recoveries ranging between 93.0 and 109.0% in the case of water samples, and between 95.0 and 103.0% in the case of human plasma, were obtained. These results were compared with the results obtained by other methods.