Test solution— Transfer about 1 g of Mannitol, accurately weighed, to a 100-mL volumetric flask, and add 40 mL of ammonium molybdate solution (1 in 10), which previously had been filtered if necessary. Add 20 mL of 1 N sulfuric acid, dilute with water to volume, and mix.

Mobile phase— Use degassed water.

Resolution solution— Dissolve sorbitol and USP Mannitol RS in water to obtain a solution having concentrations of about 4.8 mg per mL of each.

Standard preparation— Dissolve an accurately weighed quantity of USP Mannitol RS in water, and dilute quantitatively with water to obtain a solution having a known concentration of about 4.8 mg per mL.

Assay preparation— Transfer about 0.24 g of Mannitol, accurately weighed, to a 50-mL volumetric flask, dissolve in 10 mL of water, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a refractive index detector that is maintained at a constant temperature and a 4-mm × 25-cm column that contains packing L19. The column temperature is maintained at a temperature between 30 and 85 controlled within ±2 of the selected temperature, and the flow rate is about 0.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%. In a similar manner, chromatograph the Resolution solution: the resolution, R, between the sorbitol and mannitol peaks is not less than 2.0.

Procedure— Separately inject equal volumes (about 20 µL) of the Assay preparation and the Standard preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C6H14O6, in the Mannitol taken by the formula: in which C is the concentration, in mg per mL, of USP Mannitol RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.