A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

B: It meets the requirements of the test for Specific rotation 781S.

C: Add 3 mL of a solution (1 in 5) to 5 mL of hot alkaline cupric tartrate TS: a copious red precipitate of cuprous oxide is formed.

Test solution: 10 mg per mL, in water.

Test solution— Accurately weigh about 2.5 g of Tagatose, and dissolve in a mixture of 4 mL of sulfuric acid and 5 mL of hydrochloric acid. Transfer the solution to a 50-mL volumetric flask, dilute with water to volume, and mix.

Standard lead solution— Dissolve 1.60 g of lead nitrate in diluted nitric acid (10 mL of nitric acid diluted with 20 mL water, boiled to remove nitrous fumes, and cooled), and dilute with water to 1000 mL. Dilute 10.0 mL of this solution with water to 500 mL. This solution contains the equivalent of 20 µg of lead per mL.

Calibration solutions— To a series of 100-mL volumetric flasks, pipet 0, 1, 2, 3, 4, and 5 mL of the Standard lead solution, and dilute with water to about 50 mL. Add 8 mL of sulfuric acid and 10 mL of hydrochloric acid to each flask, shake to dissolve, and dilute with water to volume. These solutions contain 0, 0.2, 0.4, 0.6, 0.8, and 1.0 µg of lead per mL.

Procedure— Concomitantly determine the absorbances of the Calibration solutions and the Test solution at the wavelength of maximum absorbance at 283.3 nm, with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851). Plot the absorbances of the Calibration solutions versus the concentration of lead. Using this graph, determine the concentration of lead in the Test solution. Not more than 1 µg per g is found.

Mobile phase— Prepare a solution in water containing 50 mg of calcium acetate per L.

Standard preparation— Dissolve an accurately weighed quantity of USP Tagatose RS in water to obtain a solution having a known concentration of about 5 mg per mL. Pass through a 0.2-µm filter.

Assay preparation— Transfer about 50 mg of Tagatose, previously dried, to a 10-mL volumetric flask, and dissolve in about 8 mL of water. Dilute with water to volume, and pass through a 0.2-µm filter.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a refractive index detector and a 7.8-mm × 30-cm column that contains 9-µm packing L19. The column temperature is maintained at 85. The flow rate is about 0.6 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%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C6H12O6 in the portion of Tagatose taken by the formula: in which C is the concentration, in mg per mL, of USP Tagatose RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.