Fig. 6
The second-order derivative spectrograms show nicotinamide spectrum 10 µg/mL (A), nicotinamide series (A1–A6), tretinoin 2 µg/mL (B), solution formula (S), and cream formula (C)
Fig. 6 | BMC Chemistry
The second-order derivative spectrograms show nicotinamide spectrum 10 µg/mL (A), nicotinamide series (A1–A6), tretinoin 2 µg/mL (B), solution formula (S), and cream formula (C)