Printed on: Wed Aug 11 2021, 06:25:36 PM (EST) Printed by: Le Tran Published on: 01-Jun-2021 @2021 USPC
Not official text of the USP-NF. Please refer to the currently official version of the individual Reagent, Solution, or Indicator document for compliance purposes
Indicator and Test Papers
1. DEFINITION Litmus Paper, Red—Usually about 6 × 50 mm in size. Red
litmus paper meets the requirements of the tests for
Indicator and test papers are strips of paper of suitable
Phosphate, Residue on Ignition, and Rosin Acids, under Litmus
dimension and grade impregnated with an indicator or a
Paper, Blue.
reagent to provide a convenient form of the impregnated
Sensitiveness: Drop a 10- to 12-mm strip into 100 mL of
substance.
0.0005 N sodium hydroxide contained in a beaker, and stir
Some test papers may be obtained from commercial
continuously: the color of the paper changes within 30
sources of laboratory supplies. Alternatively, they may be
seconds. The 0.0005 N sodium hydroxide is prepared by
prepared in the laboratory.
diluting 1 mL of 0.1 N sodium hydroxide with freshly boiled
and cooled purified water to 200 mL.
2. PREPARATION OF INDICATOR AND TEST PAPERS
Wet white filter paper completely with hydrochloric acid, Mercuric Bromide Test Paper—Place a 50 mg/mL solution of
and wash with water until the last washing does not produce a mercuric bromide in dehydrated alcohol in a dish, and
red color when treated with methyl red TS. Then treat with immerse in it pieces of white filter paper weighing 80 g/m2
ammonia TS, and wash again with water until the last washing (speed of filtration = filtration time expressed in s for 100 mL
does not produce a red color when treated with of water at 20° with a filter surface of 10 cm2 and a constant
phenolphthalein TS. pressure of 6.7 kPa; 40–60 s), each measuring 1.5 cm by 20 cm
Carefully dry in still air, unless otherwise specified, by and folded in the middle. Allow the excess of liquid to drain,
suspending it from rods of glass or other inert material in a and allow the paper to dry, protected from light, suspended
space free from acid, alkali, and other fumes, saturate the over a nonmetallic thread. Discard 1 cm from each end of each
paper with the proper strength or concentration of indicator strip, and cut the remainder into 1.5-cm squares or discs of
solution, and carefully dry using the same drying procedure. 1.5-cm diameter. Store in a glass-stoppered container
Cut the paper into strips of convenient size, and store the wrapped with black paper.
papers in well-closed containers, protected from light and
moisture. Methyl Green–Iodomercurate Paper—Immerse thin strips of
suitable filter paper in a 40 g per L solution of methyl green,
Cupric Sulfate Test Paper—Use cupric sulfate TS. and allow to air-dry. Immerse the strips for 1 hour in a solution
containing 140 g per L of potassium iodide and 200 g per L
Eriochrome Black T–Sodium Chloride Indicator: Mix 0.1 g of mercuric iodide. Wash with water until the washings are
of eriochrome black T and 10 g of sodium chloride, and practically colorless, and allow to air-dry. Store protected from
triturate until the mixture becomes homogenous. light, and use within 48 hours.
Lead Acetate Test Paper—Usually about 6 × 80 mm in size. Methyl Yellow Paper—Use a 1 in 2000 solution of methyl
Use lead acetate TS, and dry the paper at 100°, avoiding yellow in alcohol.
contact with metal.
pH Indicator Paper, Short-Range—Use a suitable grade.
Litmus Paper, Blue—Usually about 6 × 50 mm in size. It meets
the requirements of the following tests. Phenolphthalein Paper—Use a 1 in 1000 solution of
Phosphate (Reagent test): Cut 5 strips into small pieces, mix phenolphthalein in diluted alcohol.
with 500 mg of magnesium nitrate in a porcelain crucible,
and ignite. To the residue add 5 mL of nitric acid, and Starch Iodate Paper—Use a mixture of equal volumes of
evaporate to dryness: the residue shows not more than starch TS and potassium iodate solution (1 in 20).
0.02 mg of PO4.
Residue on Ignition: Ignite carefully 10 strips of the paper Starch Iodide Paper—Use a solution of 500 mg of potassium
to constant weight: the weight of the residue corresponds iodide in 100 mL of freshly prepared starch TS.
to not more than 0.4 mg per strip of about 3 square cm.
Rosin Acids: Immerse a strip of the blue paper in a solution Thiazole Yellow Paper: Use a 1 in 2000 solution of thiazole
of 100 mg of silver nitrate in 50 mL of water: the color of the yellow in water.
paper does not change in 30 seconds.
Sensitiveness: Drop a 10- to 12-mm strip into 100 mL of Turmeric Paper—Use a solution prepared as follows:
0.0005 N acid contained in a beaker, and stir continuously: Macerate 20 g of powdered turmeric, the dried root of
the color of the paper is changed within 45 seconds. The Curcuma longa Linné (Fam. Zingiberaceae), with four 100-mL
0.0005 N acid is prepared by diluting 1 mL of 0.1 N portions of cold water, decanting the clear liquid portion each
hydrochloric acid with freshly boiled and cooled purified time and discarding it. Dry the residue at a temperature not
water to 200 mL. over 100°. Macerate with 100 mL of alcohol for several days,
and filter.
Sensitiveness: Dip a strip of the paper, of about 1.5-cm
Add the following:
length, in a solution of 1.0 mg of boric acid in 5 mL of water,
▲
Litmus Paper, Neutral—Usually about 6 × 50 mm in size. previously mixed with 1 mL of hydrochloric acid. After 1
Neutral litmus paper meets the requirements of the tests for minute remove the paper from the liquid, and allow it to dry:
Phosphate, Residue on Ignition, and Sensitiveness under Litmus the yellow color changes to brown. Then moisten the paper
Paper, Blue. It changes from its original color to red in acid with ammonia TS: the color of the paper changes to greenish
conditions, and from its original color to blue in basic black.
conditions.▲ (USP 1-Aug-2019)
