Reducing sugars—
Dissolve 500 mg of Xylitol in 2.0 mL of water in a 10-mL conical flask. Into a similar flask, pipet 2 mL of a dextrose solution containing 0.5 mg per mL. Concomitantly, to each add 1 mL of
alkaline cupric tartrate TS, heat to boiling, and cool: any turbidity in the xylitol flask is not greater than that in the dextrose flask, in which a reddish brown precipitate forms (0.2%, as dextrose).
Limit of other polyols—
Using the chromatograms obtained in the
Assay, separately calculate the percentage of each polyol in the portion of Xylitol taken by the formula:
2500C/W (R U /R S),
in which
C is the concentration, in mg per mL, of the individual polyol in the
Standard preparation; W is the weight, in mg, of Xylitol taken to prepare the
Assay preparation; and
R U and
R S are the peak response ratios of the individual derivatized polyol to that of derivatized erythritol in the chromatograms of the solutions obtained from the
Assay preparation and the
Standard preparation, respectively. The sum of the polyols found, calculated on the anhydrous basis, is not more than 2.0%.
Assay—
Internal standard solution—
Transfer about 88 mg of erythritol to a 25-mL volumetric flask, dissolve in and dilute with water to volume, and mix.
Standard preparation—
Transfer accurately weighed quantities of about 25 mg each of
L-arabinitol, galactitol, mannitol, and sorbitol to a 100-mL volumetric flask. Dissolve in and dilute with water to volume, and mix. Transfer 5.0 mL of this solution to a 25-mL volumetric flask, add about 250 mg of
USP Xylitol RS, accurately weighed, dilute with water to volume, and mix.
Assay preparation—
Transfer about 250 mg of Xylitol, accurately weighed, to a 25-mL volumetric flask, dissolve in and dilute with water to volume, and mix.
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 temperature of the injection port is about 270
, and the detector temperature is about 280
. Chromatograph the solution obtained from the
Standard preparation as directed for
Procedure, and record the peak responses: 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 C
5H
12O
5 in the portion of Xylitol taken by the formula:
2500(C /W )( R U /R S ),
in which
C is the concentration, in mg per mL, of
USP Xylitol RS in the
Standard preparation; W is the weight, in mg, of Xylitol taken to prepare the
Assay preparation; and
R U and
R S 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.
;)
