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G Designations
—See phases for gas chromatography in the Chromatographic Reagents section under Chromatography 621.

Gadolinium (Gd III) Acetate Hydrate,
(CH 3CO2)3Gd·xH2O—334.38—White, crystalline, hygroscopic powder. Irritant. Use a suitable grade.

(Dulcitol), C6H14O6182.17—White crystals or crystalline powder. Stable in air. One g dissolves in 30 mL of water to yield a clear, colorless solution. Store in cool to room temperature in a dry area.
Melting range 741 : between 188 and 189.
Water, Method I 921 : not more than 0.5%.
Residue on ignition 281 : not more than 0.1%.

C41H64O14780.94—White, crystalline powder. Practically insoluble in water, in chloroform, and in ether; slightly soluble in pyridine and in diluted alcohol. Melts at about 250, with decomposition.
Specific rotation 781: between +3.8 and +4.8, determined in a solution of pyridine containing 10 mg per mL, with the use of a mercury light at 546.1 nm; between +21 and +25, determined in a solution of equal parts of chloroform and methanol containing 5 mg per mL, with the use of sodium light.
Suitability— Dissolve 10 mg each of USP Digitoxin RS, previously dried, USP Digoxin RS, previously dried, and gitoxin, respectively, in separate 5-mL portions of a mixture of 2 parts of chloroform and 1 part of methanol, and dilute each with additional solvent mixture to 10 mL. Then proceed as directed in the Identification test under Digoxin. The chromatogram of gitoxin shows one fluorescent spot, located between the digoxin and digitoxin spots.

Glacial Acetic Acid
—See Acetic Acid, Glacial.

Glass Wool
—Fine threads of glass.
Acid-soluble substances— Boil 1 g for 30 minutes with 30 mL of diluted hydrochloric acid, and filter. Evaporate the filtrate, and dry the residue at 105 to constant weight: the residue weighs not more than 5 mg (0.5%).
Heavy metals— Boil 2 g with a mixture of 25 mL each of diluted nitric acid and water for 5 minutes, and filter. Evaporate one-half of the filtrate to dryness, dissolve the residue in 10 mL of water to which 3 drops of hydrochloric acid have been added, filter if necessary, and add an equal volume of hydrogen sulfide TS to the filtrate: no darkening is produced.

D-Gluconic Acid, 50 Percent in Water,
C6H12O7196.16—Pale yellow liquid.
Assay— Dilute about 200 mg of the solution, accurately weighed, with 30 mL of water. Titrate with 0.1 N sodium hydroxide VS, determining the endpoint potentiometrically. Perform a blank determination and make any necessary correction. Each mL of 0.1 N sodium hydroxide is equivalent to 19.62 mg of C6H12O7. Not less than 49.0% is found.
Refractive index 831 : between 1.4160 and 1.4180 at 20.
Specific rotation 781 : between +9.9 and +11.9, determined as is, at 20.

C6H12O6180.2—Use a suitable grade. A white, crystalline powder, with a sweet taste. Freely soluble in water; sparingly soluble in alcohol.

C6H8O6176.12—Use a suitable grade.

Glutamic Acid,
C5H9NO4147.13[56-86-0]—Use a suitable grade.

L-Glutamic Acid,
C5H9NO4147.1[56-86-0]—White powder or white powder with a faint yellow cast. Use a suitable grade.

C5H10N2O3146.15 [56-85-9]—White, crystalline powder. Use a suitable grade.

(Glycerol) —Use ACS reagent grade Glycerol.

Glycolic Acid,
C2H4O376.05—White crystalline powder or chunks.
Assay— Inject an appropriate volume (silanized) into a gas chromatograph (see Chromatography 621) equipped with a flame-ionization detector, helium being used as the carrier gas. The following conditions have been found suitable: a 0.25-mm × 30-m capillary column coated with a 1-µm layer of phase G2. The injection port temperature is maintained at 250; the detector temperature is maintained at 300; the column temperature is maintained at 100 and programmed to rise 10 per minute to 250. The area of the C2H4O3 peak is not less than 98.5% of the total peak area.

Gold Chloride
(Chlorauric Acid), HAuCl4·3H2O—393.83—Use ACS reagent grade.
Change to read:

Guaiacol (o-Methoxyphenol),
C7H8O2124.14—Colorless to yellowish, refractive liquid. USP29 Soluble in about 65 parts of water; soluble in sodium hydroxide solution; miscible with alcohol, with chloroform, with ether, and with glacial acetic acid.
Assay— When examined by gas–liquid chromatography, it shows a purity of not less than 98%. The following conditions have been found suitable for assaying it: a 3-mm × 1.8-m stainless steel column containing liquid phase G16 on 60- to 80-mesh support S1A. Helium is the carrier gas, the injection port temperature is maintained at 180, the column temperature is maintained at 200, and the flame-ionization detector is maintained at 280. The retention time is about 8 minutes.
Refractive index 831: between 1.5430 and 1.5450, at 20.

Guanidine Hydrochloride,
CH5N3·HCl—95.53—White crystalline powder. Freely soluble in water and in alcohol.
Melting range 741 : between 178 and 189.
Chloride content— Dissolve about 400 mg, accurately weighed, in 5 mL of water. Add 5 mL of glacial acetic acid, 50 mL of methanol, and 1 drop of eosin Y TS, and titrate with 0.1 N silver nitrate VS. Each mL of 0.1 N silver nitrate is equivalent to 3.545 mg of Cl. Not less than 36.1% and not more than 37.1%, calculated on the anhydrous basis, is found.

Guanidine Isothiocyanate,
C2H6N4S—118.2[593-84-0]—White powder or colorless crystals. Use a suitable grade.

Guanine Hydrochloride,
C5H5N5O·HCl·H2O—205.60—White, crystalline powder. Melts above 250, with decomposition. Slightly soluble in water and in alcohol; soluble in acidulated water and in sodium hydroxide TS. Its solutions are not precipitated by iodine TS or by mercuric-potassium iodide TS, but form a precipitate with trinitrophenol TS.
Residue on ignition (Reagent test): negligible, from 100 mg.
Loss on drying 731 Dry it at 105 to constant weight: it loses not more than 10.0% of its weight.