“…Different techniques have been used to determine -blockers in urine, including methods based on spectrofluorimetry [6][7][8], ELISA [9,10], and chromatography [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Most of the chromatographic methods are based on gas chromatography/mass spectrometry coupling (GC/MS), requiring the derivatization of polar groups (aminopropanol chain) of compounds [11,14,[17][18][19][21][22][23]25,26].…”