Time (min) Calibration equation Correlation coefficient (r) Betahistine dihydrochloride 10 A = 0.119 + 0.085 C 0.9947 20 A = 0.155 + 0.101 C 0.9950 30 A = 0.189 + 0.107 C 0.9999 40 A = 0.089 + 0.114 C 0.9983 Etilefrine hydrochloride 10 A = -0.045 + 0.055 C 0.9928 20 A = -0.050 + 0.068 C 0.9981 30 A = -9.05 x 10-5 + 0.069 C 0.9998 40 A =  -0.053 + 0.062 C 0.9975

Table 3: Calibration equations for betahistine dihydrochloride and etilefrine hydrochloride at different fixed times over the linearity range for both drugs, in presence of constant concentration of NBD-Cl.