Parameters Extraction method with BCP BPB λmax (nm) 411 415 pH 3.0 3.0 Logarithmic stability constant 6.64 6.70 Beer’s law range (mg mL-1) 1.1–47.8 1.2–45.0 Ringbom optimum concentration range (mg mL-1) 3.5-25.0 2.2-28.0 Detection limit (mg mL-1) 0.21 0.15 e (L mol-1 cm-1) 2.75×104 2.50×104 Sandell’s sensitivity (mg cm-2 per 0.001 absorbance unit) 0.039 0.040 Regression equation a Slope (m) 0.0445 0.0439 Intercept (b) 0.0309 -0.0028 Correlation coefficient (r ) 0.9999 0.9998 Recovery % 100.30 ± 0.38 100.16 ± 0.24 aWith respect to A=mC+b, where C is the concentration (μg mL–1) and A is absorbance

Table 1: Statistical data of the regression equations for the determination of FEX with the proposed method I.