Table III.

First-Order Rate Constants (k _obs) for the Degradation of Ascorbic Acid in Cream Formulations in Light and Dark

Cream formulation		Light, k obs × 103, min–1a,b,c, ±SD				Dark, k obs × 102, day–1a,b,c, ±SD
	pH	4.0	5.0	6.0	7.0	4.0	5.0	6.0	7.0
1		0.44 ± 0.039	0.64 ± 0.062	1.00 ± 0.088	1.29 ± 0.120	1.28 ± 0.115	1.52 ± 0.099	1.91 ± 0.096	2.20 ± 0.132
2		0.42 ± 0.036	0.60 ± 0.059	0.95 ± 0.090	1.20 ± 0.108	0.91 ± 0.055	1.10 ± 0.069	1.52 ± 0.097	1.82 ± 0.097
3		0.47 ± 0.042	0.69 ± 0.066	1.07 ± 0.098	1.37 ± 0.106	1.48 ± 0.092	1.76 ± 0.097	2.20 ± 0.153	2.54 ± 0.152
4		0.56 ± 0.050	0.72 ± 0.069	1.04 ± 0.097	1.31 ± 0.101	1.37 ± 0.099	1.61 ± 0.129	2.05 ± 0.123	2.36 ± 0.165
5		0.50 ± 0.050	0.67 ± 0.064	0.97 ± 0.087	1.24 ± 0.111	1.21 ± 0.085	1.41 ± 0.080	1.75 ± 0.132	1.95 ± 0.105
6		0.61 ± 0.059	0.79 ± 0.065	1.13 ± 0.105	1.40 ± 0.138	1.62 ± 0.105	1.94 ± 0.142	2.37 ± 0.190	2.65 ± 0.188
7		0.60 ± 0.057	0.71 ± 0.067	1.08 ± 0.105	1.33 ± 0.099	1.64 ± 0.095	1.89 ± 0.132	2.22 ± 0.164	2.46 ± 0.145
8		0.53 ± 0.048	0.62 ± 0.055	0.99 ± 0.076	1.26 ± 0.103	1.43 ± 0.099	1.67 ± 0.127	1.93 ± 0.149	2.12 ± 0.142
9		0.65 ± 0.062	0.81 ± 0.080	1.17 ± 0.074	1.43 ± 0.112	1.84 ± 0.149	2.08 ± 0.162	2.51 ± 0.203	2.80 ± 0.178

^aThe rate constants at pH 4.0–7.0 represent the values for formulations a to d of each cream, respectively

^bThe values of rate constants are relative and depend on specific experimental conditions including light intensity

^c n = 3