Fig. 2

a Ratio spectrum of 40 μg/mL SF using a devisor of 10 μg/mL VP, b second derivative ratio spectrum of 40 μg/mL SF using 10 μg/mL VP divisor at Δλ = 6 nm, c second derivative spectrum of ratio spectra of 40 μg/mL SF using 10 μg/mL VP divisor superimposed with the synthetic mixture of 40 μg/mL SF and 10 μg/mL VP using 10 μg/mL VP divisor, d second derivative spectrum of ratio spectrum of 40 μg/mL SF using 10 μg/mL VP divisor at Δλ = 2 nm, e second derivative spectrum of ratio spectrum of 40 μg/mL SF using 10 μg/mL VP divisor at Δλ = 4 nm, f second derivative spectrum of ratio spectrum of 40 μg/mL SF using 10 μg/mL VP divisor at Δλ = 8 nm