Stability-Indicating Photochemical Method for the Assay of Riboflavin: Lumichrome Method

Table 3

Molar ratios of RF (5 × 10⁻⁵) and photoproducts at pH of 7.0–11.6.

pH	Time (min)	FMF/RF^a	LC/LF	% LC formed^b,c	% LF formed
7.0	180	00	2.48	20	08
	30	0.62	3.63	13	08
8.0	160	00	3.66	29	18
	30	0.36	3.60	24	16
9.0	110	00	5.31	40	25
	30	0.16	4.88	34	22
10.0	48	00	1.49	49	30
	30	0.07	1.46	44	30
11.0	36	00	2.21	57	46
	30	4.88	2.20	56	37
11.6^d	36	00	1.40	58	41
	30	0.69	1.48	53	36

The complete photolysis of RF and FMF as confirmed by disappearance of spots in TLC studies.
^bLC: RF ratio 0.58 : 1.0, conversion factor 1.724.
^cLC concentration (Table 2) = 2.89 × 10⁻⁵ M.
^dRF concentration = 2.89 × 10⁻⁵  × 1.724 = 4.98 × 10⁻⁵ M = 1.876 mg/100 mL.