Each of the clinical samples analyzed using the TLC method described above were also analyzed using traditional gold standard HPLC method. A 100 µl sample of patient plasma was spiked with 50 µl of ethanol containing 120 µg/L EPI as the internal standard. Then 100 µl of a solution of phosphate buffer (pH 8.5) and 1000 µl chloroform was added followed by mixing on a rotation shaker for 5 min at max intensity. The solution was then centrifuged for 5 min at 20,800g. The organic phase was then transferred to a new tube and evaporated with nitrogen at 35°C. The resulting residue was redissolved in H2O/acetonitrile 3:1 (v:v) with 0.1 % formic acid for injection into the HPLC.