Methoxsalen Topical Solution
» Methoxsalen Topical Solution is a solution of Methoxsalen in a suitable vehicle. It contains not less than 9.2 mg and not more than 10.8 mg of methoxsalen (C12H8O4) per mL.
Packaging and storage— Preserve in tight, light-resistant containers.
USP Reference standards 11
USP Methoxsalen RS Click to View Structure
Identification— Transfer a volume of Topical Solution to a 100-mL volumetric flask, and dilute quantitatively and stepwise with alcohol to obtain a concentration of about 8 µg per mL: the UV absorption spectrum of this solution exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Methoxsalen RS, concomitantly measured.
Alcohol content (if present) 611: between 66.5% and 77.0% of C2H5OH.
Assay—
Mobile phase , Internal standard preparation, Standard preparation, and Chromatographic system—Prepare as directed in the Assay under Methoxsalen.
Assay preparation— Transfer an accurately measured volume of Topical Solution, equivalent to about 20 mg of methoxsalen, to a 100-mL volumetric flask. Dilute with alcohol to volume, and mix. Transfer 2.0 mL of this solution and 2.0 mL of Internal standard preparation to a 100-mL volumetric flask. Dilute with Mobile phase to volume, and mix. Pass through a 0.45-µm disk before using.
Procedure— Proceed as directed for Procedure in the Assay under Methoxsalen. Calculate the quantity, in mg, of methoxsalen (C12H8O4) in each mL of the Topical Solution taken by the formula:
5(C/V)(RU /RS)
in which V is the volume, in mL, of Topical Solution taken, and the other terms are as defined therein.
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