A: Infrared Absorption 197K: dried over a suitable desiccant for 4 hours.

B: Add a few drops of sulfuric acid to a hot solution: the liquid becomes turbid and develops a strongly aromatic odor.

Internal standard solution— Dissolve a quantity of biphenyl in chloroform to obtain a solution containing about 20 mg per mL.

Standard preparation— Transfer about 170 mg of USP Terpin Hydrate RS, accurately weighed, to a 100-mL volumetric flask, dissolve in 5 mL of alcohol, add 5.00 mL of Internal standard solution, dilute with chloroform to volume, and mix.

Assay preparation— Transfer about 170 mg of Terpin Hydrate, accurately weighed, to a 100-mL volumetric flask, and proceed as directed under Standard preparation, beginning with “dissolve in 5 mL of alcohol.”

Chromatographic system— Under typical conditions, the gas chromatograph is equipped with a flame-ionization detector, and it contains a 3.5-mm × 1.2-m glass column packed with 6% G1 on support S1A; the injection port and the detector temperatures are maintained at 260, and the column temperature at 120; and nitrogen is used as the carrier gas, at a flow rate necessary to yield approximate retention times of 7 minutes for terpin and 11 minutes for biphenyl.

System suitability test— Chromatograph the Standard preparation, and record the chromatograms as directed for Procedure: the resolution, R, between the terpin and biphenyl peaks is not less than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Inject about 1 µL of the Standard preparation into a suitable gas chromatograph, and record the chromatogram. Similarly, inject about 1 µL of the Assay preparation, and record the chromatogram. Calculate the quantity, in mg, of C10H20O2 in the portion of Terpin Hydrate taken by the formula: in which WS is the weight, in mg, of USP Terpin Hydrate RS, calculated on the anhydrous basis; and RU and RS are the area-ratios of terpin to the internal standard obtained from the chromatograms for the Assay preparation and the Standard preparation, respectively.