Parameters GBP-NIN GBP-DDQ GBP-TCNE GBP-MO GBP-PA λmax (nm) 580 nm 315 nm 340 nm 464 342 Linearity range µgmL-1 2-22 32-80 40-360 12-96 15-135 Molar absorptivity 632 2857 406 1542 2174 Slope 0.0037 0,0287 0.0240 0.008 0.0063 Intercept -0.0166 -0.8723 -0.0143 0.0472 0.1851 Correlation coefficient 0.9985 0.9998 0.9999 0.9981 0.9983 LOD ngmL-1 320 150 680 960 410 LOQ µgmL-1 0.96 0.44 2.06 2.92 1.23

Table 1: Optimum conditions and analytical parameters.