Test specimen: undried.

100(CS / CU)(RU / RS)

Internal standard solution— Dissolve an accurately weighed quantity of USP Erythritol RS in water to obtain a solution having a known concentration of about 3.5 mg per mL of erythritol.

Standard preparation— Dissolve accurately weighed quantities of USP l-Arabinitol RS, USP Galactitol RS, USP Mannitol RS, USP Sorbitol RS, and USP Xylitol RS in water to obtain a solution having a known concentration of 0.05 mg per mL each of l-arabinitol, galactitol, mannitol, and sorbitol; and 10 mg per mL of xylitol.

Assay preparation— Dissolve an accurately weighed quantity of Xylitol in water to obtain a solution having a concentration of about 10 mg per mL.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 0.25-mm × 30-m capillary column bonded with a 0.25-µm layer of phase G46. The carrier gas is helium, flowing at a rate of about 1 mL per minute. The chromatograph is programmed to maintain the column temperature at 170 for 5 minutes, then to increase the temperature at a rate of 6 per minute to 215, holding at that temperature for 8 minutes, then to increase the temperature at a rate of 10 per minute to 270, which is held for 14 minutes. The injection port temperature is maintained at about 270, and the detector temperature is maintained at about 280. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times corresponding to the derivatives of erythritol, l-arabinitol, xylitol, mannitol, galactitol, and sorbitol are about 0.47, 0.75, 0.81, 0.98, 0.99, and 1.0, respectively; and the relative standard deviation for the peak area ratios of xylitol to erythritol for replicate injections is not more than 1.5%.

Procedure— Transfer 1.0 mL each of the Standard preparation and the Assay preparation to separate round-bottom, 10-mL boiling flasks. To each flask, add 1.0 mL of Internal standard solution, and evaporate each of the mixtures under reduced pressure to dryness on a water bath at 60, with the aid of a rotary evaporator. Add 1 mL of dehydrated alcohol, shake gently, and evaporate to dryness under the same conditions. Dissolve each residue in 1 mL of pyridine. Add 1 mL of acetic anhydride to each flask, cap each flask, and mix on a vortex mixer for 30 seconds. Store the closed flasks in an oven at 70 for 30 minutes. Separately inject equal volumes (about 1 µL) of the solutions obtained from the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the percentage of C5H12O5 in the portion of Xylitol taken by the formula: in which CS and CU are the concentrations, in mg per mL, of xylitol in the Standard preparation and the Assay preparation, respectively; and RU and RS are the peak area ratios of derivatized xylitol to derivatized erythritol in the chromatograms of the solutions obtained from the Assay preparation and the Standard preparation, respectively.