(a'' voe ben' zone).
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C20H22O3 310.40

1,3-Propanedione, 1-[4-(1,1-dimethylethyl)phenyl]-3-(4-methoxyphenyl)-.
1-(p-tert-Butylphenyl)-3-(p-methoxyphenyl)-1,3-propanedione [70356-09-1].
» Avobenzone contains not less than 95.0 percent and not more than 105.0 percent of C20H22O3, calculated on the dried basis.
Packaging and storage— Preserve in tight, light-resistant containers.
USP Reference standards 11
USP Avobenzone RS Click to View Structure
B: Ultraviolet Absorption 197U
Solution: 5 µg per mL.
Medium: alcohol.
Absorptivities at 360 nm do not differ by more than 3.0%.
Melting range, Class I 741: between 81 and 86.
Loss on drying 731 Dry it in vacuum at 70 for 4 hours: it loses not more than 0.5% of its weight.
Chromatographic purity—
Test solution— Proceed as directed for Assay preparation in the Assay.
Chromatographic system (see Chromatography 621)— Proceed as directed in the Assay.
Procedure— Inject a volume (about 1 µL) of Test solution into the chromatograph, record the chromatogram, and measure the peak responses. Calculate the percentage of each impurity in the portion of Avobenzone taken by the formula:
100(rI / rS)
in which rI is the response of each individual peak, other than the avobenzone peak, in the chromatogram of the Test solution; and rS is the sum of the responses of all of the peaks in the chromatogram of the Test solution: not more than 3.0% of any individual impurity is found, and the sum of all of the impurities is not more than 4.5%.
Standard preparation— Dilute an accurately measured quantity of USP Avobenzone RS in acetone, and dilute quantitatively, and stepwise if necessary, with acetone to obtain a solution having a known concentration of about 50 mg per mL.
Assay preparation— Transfer about 500 mg of Avobenzone, accurately weighed, to a 10-mL volumetric flask, dilute with acetone to volume, and mix.
Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 0.32-mm × 25-m fused silica capillary column coated with phase G1. The column temperature is maintained at about 200 until the time of injection, then increased at a rate of 4 per minute to 280. The injection port temperature is maintained at 200, and the detector temperature is maintained at about 280. Helium is used as the carrier gas. The split ratio is 50:1. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between avobenzone and any adjacent peak is not less than 1.0; and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure— Separately inject equal volumes (about 1 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C20H22O3 in the portion of Avobenzone taken by the formula:
10C (rU / rS)
in which C is the concentration, in mg per mL, of USP Avobenzone RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
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Monograph Feiwen Mao, M.S.
Senior Scientific Liaison
(SM32010) Monographs - Small Molecules 3
Reference Standards RS Technical Services
USP35–NF30 Page 2274
Pharmacopeial Forum: Volume No. 33(5) Page 872