Figure 5.

Calibration curves prepared from the quinine standard solutions using the external (A) and the internal (B) standard addition methods. The linear best-fit lines, linear regression equations, and correlation coefficients are displayed for each group in panel A (n = 5). Data were collected at excitation and emission wavelengths of 350 nm and 450 nm, respectively, with a PMT voltage of 600 V and slit widths set to 5 nm each. The Canada Dry tonic water sample was used for the internal standard (S_i) method in panel B, and the fluorescence intensity is an average of two replicates (n =2). Standard deviations are represented by the error bars.