Factor Xa (Activated Factor X) for Anti-Factor Xa Test —Factor Xa is the proteolytic enzyme derived from bovine plasma, and it cleaves prothrombin to form thrombin. It is a glycoprotein having a molecular weight of 40,000. One Factor Xa Unit is the amount of activated endogenous Factor X (55,000 Da when nonactivated) that is contained in 1 mL of normal plasma. Russell's viper venom is used to activate the enzyme, and is then removed. The preparation is stabilized and lyophilized.
Factor Xa is free of thrombin at the concentration used in the test. When tested against pure fibrinogen, no clotting takes place within 24 hours. It has not less than 40 Factor Xa Units per mg of protein, and exhibits 90% homogeneity when tested by disk electrophoresis.
One Factor Xa Unit per mL gives a 15-second clotting time when tested in the following manner. Mix 0.1 mL of a saturated solution of cephalin (derived from rabbit brain-acetone powder or from an equivalent amount of rabbit brain thromboplastin) in 0.1 mL of citrated bovine plasma and 0.1 mL of 0.025 M calcium chloride. Immediately add 0.1 mL of a solution of factor Xa (1 in 10), and incubate at 37.

Fast Blue B Salt, C14H12N4O2·ZnCl4—475.47 [91-91-8]—Green powder.
Loss on drying 731— Dry it in vacuum at 110 for 1 hour: it loses not more than 5.0% of its weight.
Absorbance— Dissolve 50 mg in 100 mL of water. In a second container dissolve 100 mg of 2-naphthol in 100 mL of 2-methoxyethanol. Pipet 5 mL of the test solution and 10 mL of the 2-naphthol solution into a 100-mL volumetric flask, and dilute with acetone to volume. For the blank, pipet 5 mL of water and 10 mL of 2-naphthol solution into a second 100-mL volumetric flask, and dilute with acetone to volume. Determine the absorbance of the test solution in a 1-cm cell at the wavelength of maximum absorbance at about 545 nm, with a suitable spectrophotometer, using the blank to set the instrument: the absorbance is not less than 0.80.

Fast Blue BB Salt, (C17H18ClN3O3)2·ZnCl2—831.89 [15710-69-7]—Yellow powder melting at about 162, with decomposition. Sparingly soluble in water.
Chloride— Transfer about 80 mg, accurately weighed, to a suitable beaker. Add 25 mL of acetone, 25 mL of water, and 500 mg of sodium nitrate. Stir until solution is complete. Titrate with 0.01 N silver nitrate VS, determining the endpoint potentiometrically. Perform a blank determination and make any necessary correction. Not less than 15.0% of chloride is found.

Fast Green FCF, C37H34N2Na2O10S3—808.86 [2353-45-9]—Red to brown-violet powder or crystals. Soluble in water; sparingly soluble in alcohol. Use a suitable grade.

FD&C Blue No. 1 (Brilliant Blue), C37H34N2O9S3Na2—792.86 [3844-45-9]—Use a suitable grade.

Ferric Ammonium Citrate —Thin, transparent, garnet-red scales or granules or brownish-yellow powder. Is deliquescent and is affected by light. Very soluble in water; insoluble in alcohol.
Assay— Accurately weigh about 1 g, dissolve in 25 mL of water in a glass-stoppered flask, add 5 mL of hydrochloric acid and 4 g of potassium iodide, insert the stopper in the flask, and allow to stand in the dark for 15 minutes. Add 100 mL of water, and titrate the liberated iodine with 0.1 N sodium thiosulfate VS, adding 3 mL of starch TS as the endpoint is approached. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N sodium thiosulfate is equivalent to 5.585 mg of Fe: between 16.5% and 18.5% is found.
Ferric citrate— To 250 mg dissolved in 25 mL of water add 1 mL of potassium ferrocyanide TS: no blue precipitate is formed.
Tartrate— Dissolve 1 g in 10 mL of water, add 1 mL of potassium hydroxide TS, boil to coagulate the ferric hydroxide, adding more potassium hydroxide TS, if necessary, to precipitate all of the iron, filter, and slightly acidify the filtrate with glacial acetic acid. Add 2 mL of glacial acetic acid, and allow to stand for 24 hours: no crystalline white precipitate is formed.
Lead 251— Dissolve 1.0 g in 30 mL of water, add 5 mL of dilute nitric acid (1 in 21), boil gently for 5 minutes, cool, and dilute with water to 50 mL: 20 mL of the solution shows not more than 0.008 mg of Pb (0.002%).

Ferric Ammonium Sulfate, FeNH4(SO4)2·12H2O—482.19—Use ACS reagent grade.

Ferric Chloride, FeCl3·6H2O—270.29 [10025-77-1]—Use ACS reagent grade.

Ferric Nitrate, Fe(NO3)3·9H2O—404.00 [10421-48-4]—Use ACS reagent grade.

Ferric Sulfate, Fe2(SO4)3·xH2O[10028-22-5]—Grayish-white, hygroscopic powder, or fawn-colored pearls, slowly soluble in water.
Assay— Accurately weigh about 700 mg, and dissolve it in a mixture of 50 mL of water and 3 mL of hydrochloric acid in a glass-stoppered flask. Add 3 g of potassium iodide, and allow to stand in the dark for 30 minutes. Then dilute with 100 mL of water, and titrate with 0.1 N sodium thiosulfate VS, adding 3 mL of starch TS as the endpoint is approached. Each mL of 0.1 N sodium thiosulfate is equivalent to 5.585 mg of Fe: not less than 21.0% and not more than 23.0% is found.
Insoluble matter (Reagent test)— A 10-g portion, dissolved in a mixture of 100 mL of water and 5 mL of sulfuric acid, shows not more than 2 mg of insoluble matter (0.02%).
Chloride— Dissolve 1 g by warming with a mixture of 10 mL of water and 1 mL of nitric acid, add 4 mL of additional nitric acid, and dilute with water to 50 mL. To 25 mL add 1 mL of phosphoric acid and 1 mL of silver nitrate TS. Any turbidity does not exceed that produced in a control containing 0.01 mg of chloride ion (Cl), 1 mL of nitric acid, 1 mL of phosphoric acid, and 1 mL of silver nitrate TS (0.002%).
Ferrous iron— Dissolve 4 g by warming with 50 mL of dilute sulfuric acid (1 in 10), cool, and titrate with 0.1 N potassium permanganate: not more than 0.16 mL is required to produce a permanent pink color (0.02% as Fe+2). [Note—Because the reagents used in the tests for Copper and Zinc may contain excessive amounts of copper and zinc, they should first be purified by extracting with Dithizone Extraction Solution(see Lead 251). ]
Copper— Dissolve 1.2 g in 100 mL of water. To 10 mL add 50 mL of a solution containing 5 g of ammonium tartrate and 5 mL of ammonium hydroxide. Add 10 mL of Standard Dithizone Solution (see Lead 251), shake for 2 minutes, draw off the dithizone layer, and compare the pink color with that in a control containing 6 µg of copper ion (Cu) and treated exactly as the 10-mL portion of test solution. If the color in the test solution is less than that in the control, then the test specimen contains less than the limit of both Copper and Zinc. If the color in the test solution is more than that in the control, add 15 mL of dilute hydrochloric acid (1 in 250), and shake for 2 minutes. Draw off the dithizone solution, and shake with a second 15 mL of dilute hydrochloric acid (1 in 250) for 2 minutes. Draw off the dithizone, combine the two acid extracts, and reserve for the Zinc test. Any pink color in the dithizone solution is not darker than that in the control solution treated exactly as the test solution (0.005%).
Zinc— To the combined acid extracts saved from the Copper test, add 0.5 M sodium acetate to bring the pH between 5.0 and 5.5, and then add 1 mL of 0.1 N sodium thiosulfate. Add 10 mL of Standard Dithizone Solution (see Lead 251), shake for 2 minutes, and allow the layers to separate. Draw off the dithizone, and discard the water layer. Any pink color is not greater than that in a control prepared by adding 0.006 mg of zinc ion (Zn) to the combined acid extracts from the control used in the test for Copper (0.005%).
Nitrate— Dissolve 10 g in 100 mL of dilute sulfuric acid (1 in 100), heat to boiling, and pour, slowly, into a mixture of 140 mL of water and 50 mL of stronger ammonia TS. Filter through a folded filter while still hot, wash with hot water until the volume of the filtrate is 300 mL, mix, and cool. To 15 mL of this solution add 1 mL of sodium chloride solution (1 in 200), 0.10 mL of indigo carmine TS, and 15 mL of sulfuric acid. The blue color is not completely discharged at the end of 5 minutes (0.01%).
Substances not precipitated by ammonia— Evaporate to dryness 30 mL of the filtrate obtained in the test for Nitrate, and ignite gently: the weight of residue does not exceed 1 mg (0.10%).

Ferrocyphen (Dicyano-bis (1,10-phenantroline) iron (II) Complex), (C12H8N2)2Fe(CN)2—468.3—Brown to black powder. Dark red solution at 10 mg per mL in glacial acetic acid. Soluble in chloroform and in water at 5 mg per mL, yielding a clear purple solution in chloroform and a clear orange solution in water.
Water, Method I 921: not more than 10%.

Ferrous Chloride Tetrahydrate (Iron (II) Chloride Tetrahydrate), FeCl2·4HO—198.81[13478-10-9]—Use a suitable grade with a content of NLT 99.0%.

Ferrous Sulfate, FeSO4·7H2O—278.02 [7782-63-0]—Use ACS reagent grade.

Ferrous Ammonium Sulfate, Fe(NH4)2(SO4)2·6H2O—392.14—Use ACS reagent grade.

Ferulic Acid (4-Hydroxy-3-methoxycinnamic acid), C10H10O4—194.19 [1135-24-6]—Use a suitable grade.

Fibroblast Growth Factor-2— Use a suitable grade.
[Note—A suitable grade can be obtained from Roche Diagnostics Corporation, www.roche-diagnostics.com. ]

Filter Paper, Quantitative —For the Mercuric Bromide Test Paper used in testing for arsenic, use Swedish O filter paper or other makes of like surface, quality, and ash.

Fluorene, C13H10—166.22 [86-73-7]—White to off-white crystals or powder. Soluble in benzene, in carbon disulfide, in ether, and in hot alcohol; freely soluble in glacial acetic acid.
Solubility test— One g dissolves in 10 mL of acetone to yield a clear and complete solution.
Melting range 741 : between 113 and 117, within a 2 range.

9-Fluorenylmethyl Chloroformate, C15H11ClO2—258.70 [28920-43-6]—Clear, colorless solid. Melts at about 62.

Fluorescamine, C17H10O4—278.26 [38183-12-9]—White to off-white powder. Very slightly soluble in water; freely soluble in methylene chloride; soluble in alcohol; slightly soluble in chloroform.
Assay— Dissolve about 600 mg in 75 mL of dimethylformamide, and titrate with 0.1 N lithium methoxide to a blue endpoint, using 1% thymol blue in dimethylformamide as the indicator. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N lithium methoxide is equivalent to 27.83 mg of C17H10O4. Not less than 99% is found.
Loss on drying 731— Dry it at 105 for 4 hours: it loses not more than 0.5% of its weight.

4¢-Fluoroacetophenone, FC6H4COCH3—138.14 [403-42-9]—Colorless liquid.
Assay— Inject an appropriate specimen into a suitable 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 25-mm × 30-m capillary column coated with a 1-µm layer of phase G2; the injection port temperature is maintained at 200; the detector temperature is maintained at 250; the column temperature is maintained at 100 and programmed to rise 10 per minute to 250. The area of the FC6H4COCH3 peak is not less than 99% of the total peak area.
Refractive index 831: 1.510 at 20.

Formaldehyde Solution, HCHO—(30.03) and water—Use ACS reagent grade.

Formamide, HCONH2—45.04 [75-12-7]—Use ACS reagent grade.
Preparation for Digitoxin Assay— To ensure freedom from ammonia, treat Formamide as follows. Shake a suitable quantity of formamide with about 10% of its weight of anhydrous potassium carbonate for 15 minutes, and filter. Distill the filtrate in an all-glass apparatus under vacuum at a pressure of about 25 mm of mercury or less. Reject the first portion of distillate containing water, and collect the fraction that boils at about 115 at a pressure of 25 mm of mercury or at 101 at a pressure of 12 mm of mercury. Store in tight containers, protected from light.

Formamide, Anhydrous, HCONH2—45.04 [75-12-7]—Use formamide that has a water content of less than 0.1%.

Formic Acid, HCOOH—46.03 [64-18-6]—Use ACS reagent grade Formic Acid, 88 Percent.

Formic Acid, 96 Percent, HCOOH—46.03 [64-18-6]—Use ACS reagent grade Formic Acid, 96 Percent.

Formic Acid, Anhydrous —Use ACS reagent grade Formic Acid, 96 Percent.

Change to read:
Fuchsin, Basic (Basic Red 9, Parafuchsin Hydrochloride), C19H17N3·HCl1S (USP38) —323.82[569-61-9]—Use a suitable grade.

Fuller's Earth, Chromatographic —(Very Fine and Moderately Coarse)—Gray or grayish-white powder or granules consisting mainly of hydrous aluminum-magnesium silicate.
Powder fineness— See Powder Fineness 811.
Soluble matter— Twenty g, treated with 50 mL of cold water and filtered, yields not more than 60 mg of residue upon evaporation of the filtrate (0.3%). A second 20-g portion, treated with 50 mL of cold alcohol and filtered, yields not more than 14 mg upon evaporation of the filtrate (0.07%).
Loss on drying 731— Dry it at 105 for 6 hours: it loses between 7.0% and 10.0% of its weight.
[Note—Adjust the water content, if necessary, by drying in vacuum at room temperature, restoring the water required, and equilibrating by shaking for 2 hours. ]

Fuming Nitric Acid —See Nitric Acid, Fuming.

Fuming Sulfuric Acid —See Sulfuric Acid, Fuming.

Furfural (2-Furancarboxyaldehyde; 2-Furaldehyde), C4H3OCHO—96.08[98-01-1]—Use ACS reagent grade.

Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Reagent Margareth R. C. Marques, Ph.D.
Senior Scientific Liaison
(301) 816-8106		 (HDQ) Headquarters