Phenol solution, Standard solution, Test solution, and Chromatographic system— Prepare as directed under Chromatographic purity.

Procedure— Separately inject equal volumes (about 1 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak area responses. Calculate the percentage of phenol in the portion of Phenoxyethanol taken by the formula: in which C is the concentration, in mg per mL, of phenol in the Standard solution; W is the weight of Phenoxyethanol, in mg, taken to prepare the Test solution; and rU and rS are the peak areas of the phenol peak in the chromatograms obtained from the Test solution and the Standard solution, respectively: not more than 0.1% is found.

Phenol solution— Prepare a solution of phenol in isopropyl alcohol having a known concentration of about 0.25 mg of phenol per mL.

Standard solution— Dissolve an accurately weighed quantity of USP Phenoxyethanol RS in Phenol solution to obtain a solution having a known concentration of about 5 mg of phenoxyethanol per mL. Accurately transfer 500 µL of this solution to a vial, add 1000 µL of isopropyl alcohol, crimp the vial, and mix on a vortex mixer for about 15 seconds. Calculate the concentrations of phenoxyethanol and phenol in this solution.

Test solution— Accurately transfer 500 µL of Phenoxyethanol to a tared vial, and determine the weight of Phenoxyethanol taken. Add 1000 µL of isopropyl alcohol, crimp the vial, and mix on a vortex mixer for about 15 seconds.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 0.32-mm × 10-m capillary column coated with a 5-µm film of stationary phase G27. The carrier gas is helium with a split flow rate of 44 mL per minute. The chromatograph is programmed as follows. Initially the temperature of the column is equilibrated at 80, then the temperature is increased at a rate of 8 per minute to 260, and maintained at 260 for 10 minutes. The injection port temperature and the detector temperature are both maintained at 300. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the resolution, R, between phenol and phenoxyethanol is not less than 10; and the relative standard deviation for replicate injections for the phenoxyethanol peak is not more than 2.0%.

Procedure— Separately inject equal volumes (about 1 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak area responses. Calculate the percentage of total impurities in the portion of Phenoxyethanol taken by the formula: in which C is the concentration, in mg per mL, of phenoxyethanol in the Standard solution; W is the weight of Phenoxyethanol, in mg, taken to prepare the Test solution; rU is the sum of all additional peak areas in the chromatogram obtained from the Test solution, excluding the main peak, the solvent peak, and the phenol peak; and rS is the peak area of the phenoxyethanol peak in the chromatogram obtained from the Standard solution: not more than 1.0% of total impurities is found.

Phenol solution and Chromatographic system— Prepare as directed under Chromatographic purity.

Standard preparation— Use the Standard solution, prepared as directed under Chromatographic purity.

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 peak area responses. Calculate the quantity, in mg, of C8H10O2 in the portion of Phenoxyethanol taken by the formula: in which C is the concentration, in mg per mL, of USP Phenoxyethanol RS in the Standard preparation; and rU and rS are the responses of the phenoxyethanol peak obtained from the Assay preparation and the Standard preparation, respectively.