Packaging and storage— Preserve in tight containers.

USP Reference standards á11ñ— USP Diethyltoluamide RS.

Identification— It responds to the Identificationtest under Diethyltoluamide.

Alcohol content(if present)á611ñ: between 29.0%and 89.0%of C2H5OH.

Assay— Transfer an accurately weighed quantity of Topical Solution,equivalent to about 200mg of diethyltoluamide,to a beaker.Place the beaker in a vacuum oven containing silica gel and calcium chloride,and adjusted to a pressure of about 380mm of mercury,and heat at 35for 6hours.Transfer the residue with the aid of carbon disulfide to a 10-mLvolumetric flask,and carbon disulfide to volume,and mix.Transfer to a 10-mLvolumetric flask about 200mg of USP Diethyltoluamide RS,accurately weighed,add carbon disulfide to volume,and mix,to obtain the Standard solution.Concomitantly determine the absorbances of both solutions in 1-mm cells at the wavelength of maximum absorbance at about 14.1µm and at the wavelength of minimum absorbance at about 14.4µm,with a suitable IRspectrophotometer,using carbon disulfide as the blank.Calculate the quantity,in mg,of the meta-isomer of diethyltoluamide (C12H17NO)in the portion of Topical Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Diethyltoluamide RSin the Standard solution,and AUand ASare the absorbances of the solution from Diethyltoluamide Solution and the Standard solution,respectively,at the wavelengths indicated by the subscripts.

Expert Committee:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 638

Phone Number:1-301-816-8394