Fig. 6

Effect of NBD-Cl volume on absorbance a and on fluorescence intensity b of the reaction product. Effect of buffer pH on absorbance c and on fluorescence intensity d of the reaction product. Effect of buffer volume on absorbance e and fluorescence intensity f of the reaction product. Effect of heating temperature on absorbance g and fluorescence intensity h of the reaction product. Effect of heating time on absorbance i and fluorescence intensity j of the reaction product. Effect of HCl volume on absorbance k and fluorescence intensity l of the reaction product. For absorbance measurements, 50 μg/mL of VP was used with 0.2% w/v NBD-Cl and for fluorescence intensity measurements, 10 μg/mL of VP was used with 0.2% w/v NBD-Cl