A: Infrared Absorption 197K.

B: 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.

Medium: 0.06 N hydrochloric acid (prepared by adding 51 mL of hydrochloric acid to 10 L of water); 900 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Mobile phase— Proceed as directed in the Assay.

Standard stock solution— Dissolve an accurately weighed quantity of USP Gabapentin RS in the Medium to obtain a final solution having a known concentration of about 1.1 mg per mL.

Working standard solutions— Dilute aliquots of the Standard stock solution with Medium to obtain solutions having the following concentrations: 110 µg per mL for Tablets labeled to contain 100 mg; 330 µg per mL for Tablets labeled to contain 300 mg; 440 µg per mL for Tablets labeled to contain 400 mg; 660 µg per mL for Tablets labeled to contain 600 mg; and 880 µg per mL for Tablets labeled to contain 800 mg.

Test solution— Pass a portion of the solution under test through a suitable 0.45-µm filter.

Chromatographic system (see Chromatography 621)— Proceed as directed in the Assay, except to use the Working standard solutions: the column efficiency is not less than 5000 theoretical plates; the tailing factor is not more than 2.0; and the relative standard deviation for replicate injections is not more than 3%.

Procedure— Separately inject equal volumes (about 100 µL for the Tablets labeled to contain 100, 300, or 400 mg; and about 50 µL for Tablets labeled to contain 600 or 800 mg) of the appropriate Working standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the amount of gabapentin (C9H17NO2) dissolved by the formula: in which rU and rS are the peak responses for the Working standard solution and the Test solution, respectively; CS is the concentration, in mg per mL, of the Working standard solution; 900 is the volume, in mL, of Medium; 100 is the conversion factor to percentage; and L is the Tablet label claim, in mg.

Tolerances— Not less than 80% (Q) of the labeled amount of gabapentin (C9H17NO2) is dissolved in 45 minutes.

Diluent— Prepare as directed in the Assay.

Solution A— Dissolve 1.2 g of monobasic potassium phosphate in 940 mL of water, Adjust with 5 N potassium hydroxide to a pH of 6.9, add 60 mL of acetonitrile, and stir. Filter, and degas.

Solution B— Dissolve 1.2 g of monobasic potassium phosphate in 700 mL of water, adjust with 5 N potassium hydroxide to a pH of 6.9, add 300 mL of acetonitrile, and stir. Filter, and degas.

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Dissolve accurately weighed quantities of USP Gabapentin RS and USP Gabapentin Related Compound A RS in Diluent to obtain a solution having a known concentration of about 0.04 mg of each per mL.

Test solution— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 500 mg of gabapentin, to a suitable volumetric flask, and dissolve the contents in Diluent with sonication, if necessary, for about 30 seconds. Dilute with Diluent to volume, and mix to obtain a final solution having a known concentration of about 20 mg per mL, based on the label claim.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L7. The flow rate is about 1.5 mL per minute. The chromatograph is programmed as follows. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the tailing factor for the gabapentin peak is not more than 2.0; and the relative standard deviation for replicate injections for both gabapentin and gabapentin related compound A is not more than 5.0%.

Procedure— Separately inject a volume (about 50 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the percentage of gabapentin related compound A in the portion of Tablets taken by the formula: in which CS is the concentration, in mg per mL, of USP Gabapentin Related Compound A RS in the Standard solution; CT is the concentration, in mg per mL, of gabapentin in the Test solution, based on the label claim; and rU and rS are the individual peak responses for gabapentin related compound A obtained from the Test solution and Standard solution, respectively: not more than 0.4% of gabapentin related compound A is found. Calculate the percentage of any other unspecified degradation product relative to gabapentin content in the portion of Tablets taken using the formula: in which CS is the concentration, in mg per mL, of USP Gabapentin RS in the Standard solution; CT is the concentration, in mg per mL, of gabapentin in the Test solution, based on the label claim; ri is the response for each unspecified impurity in the Test solution; and rS is the peak response for gabapentin in the Standard solution: not more than 0.1% of any individual unspecified degradation product is found; and not more than 1.0% of total impurities is found.

Diluent— Dissolve 1.2 g of monobasic potassium phosphate in 1 L of water. Adjust with 5 N potassium hydroxide to a pH of 6.9.

Mobile phase— Dissolve 1.2 g of monobasic potassium phosphate in 940 mL of water. Adjust with 5 N potassium hydroxide to a pH of 6.9, add 60 mL of acetonitrile, and stir. Filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Gabapentin RS in Diluent, and dilute quantitatively, and stepwise if necessary, with Diluent to obtain a solution having a known concentration of about 4.0 mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of gabapentin, to a suitable volumetric flask, and dissolve the contents in Diluent with sonication, if necessary, for about 60 seconds. Dilute with Diluent to volume, and mix to obtain a final solution having a known concentration of about 4.0 mg per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L7. The flow rate is about 1.2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 7,000 theoretical plates; the tailing factor is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the gabapentin peak. Calculate the percentage of the labeled amount of gabapentin (C9H17NO2) in the portion of Tablets taken by the formula: in which CS is the concentration, in mg per mL, of USP Gabapentin RS in the Standard preparation; CU is the concentration, in mg per mL, of gabapentin in the Assay preparation, based on the label claim; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.