GLC‐ECD Determination of 1‐(2‐Hydroxyethyl)‐ 3‐hydroxy‐7‐chloro‐1,3‐dihydro‐5‐(O‐fluorophenyl)‐ 2H‐1,4‐benzodiazepin‐2‐one (SAS 643) in Plasma and Urine and Identification of Its Main Biotransformation Products