Second Supplement to USP 35–NF 30Solutions / Buffer Solutions5773
Phosphate (Reagent test)—Cut 5 strips into small pieces,card 1 cm from each end of each strip, and cut the remain-mix with 500 mg of magnesium nitrate in a porcelain cruci-der into 1.5-cm squares or discs of 1.5-cm diameter. Store ble, and ignite. To the residue add 5 mL of nitric acid, and in a glass-stoppered container wrapped with black paper. evaporate to dryness: the residue shows not more than 0.02Methyl Green–Iodomercurate Paper—Immer thin
mg of PO4.strips of suitable filter paper in a 40g per L solution of Residue on ignition—Ignite carefully 10 strips of the paper methyl green, and allow to air-dry. Immer the strips for 1 to constant weight: the weight of the residue corresponds hour in a solution containing 140g per L of potassium io-to not more than 0.4 mg per strip of about 3 square cm.dide and 200g per L of mercuric iodide. Wash with water Rosin acids—Immer a strip of the blue paper in a solu-until the washings are practically colorless, and allow to air-tion of 100 mg of silver nitrate in 50 mL of water: the color dry. Store protected from light, and u within 48 hours.
of the paper does not change in 30 conds.Methyl Yellow Paper—U a 1 in 2000 solution of Sensitiveness—Drop a 10- to 12-mm strip into 100 mL of methyl yellow in alcohol.
0.0005 N acid contained in a beaker, and stir continuously:pH Indicator Paper, Short-Range—U a suitable grade. the color of the paper is changed within 45 conds. The Phenolphthalein Paper—U a 1 in 1000 solution of
0.0005 N acid is prepared by diluting 1 mL of 0.1 N hydro-phenolphthalein in diluted alcohol.
dart
chloric acid with freshly boiled and cooled purified water to Starch Iodate Paper—U a mixture of equal volumes of 200 mL.starch TS and potassium iodate solution (1 in 20).
Litmus Paper, Red—Usually about 6×50 mm in size. Red Starch Iodide Paper—U a solution of 500 mg of potas-litmus paper meets the requirements of the tests for Phos-sium iodide in 100 mL of freshly prepared starch TS. phate, Residue on ignition, and Rosin acids, under Litmus Pa-Thiazole Yellow Paper—U a 1 in 2000 solution of thia-per, le yellow in water.
Sensitiveness—Drop a 10- to 12-mm strip into 100 mL of Turmeric Paper—U a solution prepared as follows:
0.0005 N sodium hydroxide contained in a beaker, and stir Macerate 20g of powdered turmeric, the dried root of Cur-continuously: the color of the paper changes within 30cuma longa Linn´e (Fam. Zin
giberaceae), with four 100-mL conds. The 0.0005 N sodium hydroxide is prepared by portions of cold water, decanting the clear liquid portion diluting 1 mL of 0.1 N sodium hydroxide with freshly boiled each time and discarding it. Dry the residue at a tempera-and cooled purified water to 200 mL.ture not over 100°. Macerate with 100 mL of alcohol for Mercuric Bromide Test Paper—Place a 50 mg/mL solu-veral days, and filter.
tion of mercuric bromide in dehydrated alcohol in a dish,Sensitiveness—Dip a strip of the paper, of about 1.5-cm and immer in it pieces of white filter paper weighing length, in a solution of 1.0 mg of boric acid in 5 mL of
80g/m2 (speed of filtration = filtration time expresd in s water, previously mixed with 1 mL of hydrochloric acid. Af-for 100 mL of water at 20° with a filter surface of 10 cm2ter 1 minute remove the paper from the liquid, and allow it and a constant pressure of 6.7 kPa; 40–60 s), each measur-to dry: the yellow color changes to brown. Then moisten ing 1.5 cm by 20 cm and folded in the middle. Allow the the paper with ammonia TS: the color of the paper changes excess of liquid to drain, and allow the paper to dry, pro-to greenish black.
tected from light, suspended over a nonmetallic thread. Dis-
Solutions
physiological systems are carefully chon so as not to inter-BUFFER SOLUTIONS
fere with pharmacological activity of the medicament or
normal function of the organism. It is esntial that buffers The successful completion of many Pharmacopeial tests
ud in chemical analysis be compatible with the substance and assays requires adjustment to or maintenance of a spec-
determined and the reagents ud.
ified pH by the addition of buffer solutions. In pH measure-
ments, standard buffer solutions are required for reference
purpos. For convenience, the preparation of the solu-
Change to read:
tions is in some instances described in the ctions in which
their u is specified; i.e., five parate phosphate buffers are
Standard Buffer Solutions—Standard solutions of definite described under Antibiotics—Microbial Assays 〈81〉, and v-
pH are readily available in buffer solutions prepared from eral miscellaneous single-purpo solutions are described in
the appropriate reagents. In addition, buffer solutions, buffer the individual monographs.
tablets, and buffer solids may be obtained from commercial A solution is said to be buffered if it resists changes in the
sources in convenient prepackaged form. Such preparations activity of an ion on the addition of substances that are
are available for the entire working range in pharmaceutical expected to change the activity of that ion. Buffers are sub-
analysis, but are not recommended for pH meter standardi-stances or combinations of substances that impart this resis-
zation (e pH 〈791〉).
tance to a solution. Buffered solutions are systems in which
The required reagents are described in the ction, Re-the ion is in equilibrium with substances capable of remov-
agents. Previously dry the crystalline reagents, except the ing or releasing the ion.
boric acid s and sodium acetate trihydrate,s2S(USP35) at 110°Buffer capacity refers to the amount of material that may
to 120° for 1 hour.
be added to a solution without causing a significant change
[N OTE—Where water is specified for solution or dilution in ion activity. It is defined as the ratio of acid or ba
of test substances in pH determinations, u carbon dioxide-added (in gram-equivalents per liter) to the change in pH
free water.]
(in pH units). The capacity of a buffered solution is adjusted
power struggleStore the prepared solutions in chemically resistant, tight to the conditions of u, usually by adjustment of the con-
containers such as Type I glass bottles. U the solutions centrations of buffer substances.
within 3 months.
Buffers are ud to establish and maintain an ion activity
Standard Buffer Solutions for various ranges between pH within narrow limits. The most common systems are ud
1.2 and 10.0 may be prepared by appropriate combinationsmatthew
(a) to establish hydrogen-ion activity for the calibration of
of the solutions described herein, ud in the proportions pH meters, (b) in the preparation of dosage forms that ap-
shown in the accompanying table. The volumes shown in proach isotonicity, (c) in analytical procedures, and (d) to
the table are for 200 mL of buffer solution, except that the maintain stability of various dosage forms. Buffers ud in
5774Buffer Solutions / Solutions Second Supplement to USP 35–NF 30
volumes shown for Acetate Buffer are ud to prepare 1000 4.Boric Acid and Potassium Chloride, 0.2 M—Dissolveradar
mL of buffer solution.12.37 g of boric acid (H3BO3) and 14.91 g of potas-
1.Hydrochloric Acid, 0.2 M, and Sodium Hydroxide, 0.2sium chloride (KCl) in water, and dilute with water to
M—Prepare and standardize as directed under Volu-1000 mL.
metric Solutions. 5.Potassium Chloride, 0.2 M—Dissolve 14.91 g of potas-
中丘2.Potassium Biphthalate, 0.2 M—Dissolve 40.85 g of po-sium chloride (KCl) in water, and dilute with water to
tassium biphthalate [KHC6H4(COO)2] in water, and di-1000 mL.
lute with water to 1000 mL. 6.Acetic Acid, 2N—Prepare and standardize as directed
3.Potassium Phosphate, Monobasic 0.2 M—Dissolve under Volumetric Solutions.
27.22 g of monobasic potassium phosphate (KH2PO4)
in water, and dilute with water to 1000 mL.
Composition of Standard Buffer Solutions
Hydrochloric Acid Buffer
Place 50 mL of the potassium chloride solution in a 200-mL volumetric flask, add the specified volume of the hydrochloric acid solution, then add water to volume.
pH 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 0.2 M HCl, mL85.067.253.241.432.426.020.416.213.010.27.8
Acid Phthalate Buffer
Place 50 mL of the potassium biphthalate solution in a 200-mL volumetric flask, add the specified volume of the hydrochloric acid solution, then add water to volume.
pH 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0
limelight0.2 M HCl, mL49.542.235.428.922.315.710.4 6.3 2.90.1
Neutralized Phthalate Buffer
Place 50 mL of the potassium biphthalate solution in a 200-mL volumetric flask, add the specified volume of the sodium hydroxide solution, then add water to volume.
pH 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8
0.2 M NaOH, mL 3.0 6.611.116.522.628.834.138.842.3
Phosphate Buffer
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Place 50 mL of the monobasic potassium phosphate solution in a 200-mL volumetric flask, add the specified volume of the sodium hydroxide solution, then add water to volume.
pH 5.8 6.0 6.2 6.4 6.6 6.87.07.27.47.67.88.0
0.2 M NaOH, mL 3.6 5.68.111.616.422.429.134.739.142.444.546.1
Alkaline Borate Buffer
invalid
Place 50 mL of the boric acid and potassium chloride solution in a 200-mL volumetric flask, add the specified volume of the sodium hydroxide solution, then add water to volume.
pH8.08.28.48.68.89.09.29.49.69.810.0gotv
0.2 M NaOH, mL 3.9 6.08.611.815.820.826.432.136.940.643.7
Acetate Buffer
Place the specified amount of sodium acetate NaC2H3O2·3H2O in a 1000-mL volumetric flask, add the specified volume of the acetic acid solution, then add water to volume, and mix.
pH 4.1 4.3 4.5 4.7 4.9 5.1 5.2 5.3 5.4 5.5
pH (measured) 4.10 4.29 4.51 4.70 4.90 5.11 5.18 5.30 5.40 5.48 NaC2H3O2 · 3H2O, g 1.5 1.99 2.99 3.59 4.34 5.08 5.23 5.61 5.76 5.98
2 N CH3COOH, mL19.517.714.011.89.1 6.
3 5.8 4.
4 3.8 3.0
parison of colors is best made in layers of equal depth, and COLORIMETRIC SOLUTIONS (CS)
viewed transverly against a white background (e also
Visual Comparison under Spectrophotometry and Light-Scatter-(For the Preparation of Matching Fluids, e Color and
ing 〈851〉). It is particularly important that the solutions be Achromicity 〈631〉.)英文单词表
compared at the same temperature, preferably 25°.
The solutions are ud in the preparation of the colori-
Cobaltous Chloride CS—Dissolve about 65g of cobaltous metric standards for certain drugs, and for the carbonization
chloride (CoCl2·6H2O) in enough of a mixture of 25 mL of tests with sulfuric acid that are specified in veral
hydrochloric acid and 975 mL of water to make 1000 mL. monographs. Store the solutions in suitably resistant, tight
Pipet 5 mL of this solution into a 250-mL iodine flask, add 5 containers.
mL of hydrogen peroxide TS and 15 mL of sodium hydrox-Comparison of colors as directed in the Pharmacopeial
ide solution (1 in 5), boil for 10 minutes, cool, and add 2g tests preferably is made in matched color-comparison tubes
of potassium iodide and 20 mL of dilute sulfuric acid (1 in or in a suitable colorimeter under conditions that ensure
4). When the precipitate has dissolved, titrate the liberated that the colorimetric reference solution and that of the spec-
iodine with 0.1 N sodium thiosulfate VS, adding 3 mL of imen under test are treated alike in all respects. The com-
