INDICATOR AND TEST PAPERS
Indicator and test papers are strips of paper of suitable dimension and grade (see Filter Paper,Quantitative,in the section Reagents)impregnated with an indicator or a reagent that is sufficiently stable to provide a convenient form of the impregnated substance.Some test papers may be obtained from commercial sources of laboratory supplies.Those required in Pharmacopeial tests and assays may be prepared as directed in the following paragraphs,by means of the solutions specified,or to meet the tests set forth herein under the individual titles.
Treat strong,white filter paper with hydrochloric acid,and wash with water until the last washing no longer shows an acid reaction to methyl red.Then treat with ammonia TS,and wash again with water until the last washing is not alkaline to phenolphthalein.
After thorough drying,saturate the paper with the proper strength of indicator solutions,and carefully dry in still air,unless otherwise specified,by suspending it from rods of glass or other inert material in a space free from acid,alkali,and other fumes.
Cut the paper into strips of convenient size,and store the papers in well-closed containers,protected from light and moisture.
Cupric Sulfate Test Paper —Use cupric sulfate TS.
Lead Acetate Test Paper —Usually about 6×80mm in size.Use lead acetate TS,and dry the paper at 100,avoiding contact with metal.
Litmus Paper,Blue —Usually about 6×50mm in size.It meets the requirements of the following tests.
Phosphate (Reagent test)—Cut 5strips into small pieces,mix with 500mg of magnesium nitrate in a porcelain crucible,and ignite.To the residue add 5mLof nitric acid,and evaporate to dryness:the residue shows not more than 0.02mg of PO4.
Residue on ignition —Ignite carefully 10strips of the paper to constant weight:the weight of the residue corresponds to not more than 0.4mg per strip of about 3square cm.
Rosin acids —Immerse a strip of the blue paper in a solution of 100mg of silver nitrate in 50mLof water:the color of the paper does not change in 30seconds.
Sensitiveness —Drop a 10-to 12-mm strip into 100mLof 0.0005Nacid contained in a beaker,and stir continuously:the color of the paper is changed within 45seconds.The 0.0005Nacid is prepared by diluting 1mLof 0.1Nhydrochloric acid with freshly boiled and cooled purified water to 200mL.
Litmus Paper,Red —Usually about 6×50mm in size.Red litmus paper meets the requirements of the tests for Phosphate,Residue on ignition,and Rosin acids,under Litmus Paper,Blue.
Sensitiveness—Drop a 10-to 12-mm strip into 100mLof 0.0005Nsodium hydroxide contained in a beaker,and stir continuously:the color of the paper changes within 30seconds.The 0.0005Nsodium hydroxide is prepared by diluting 1mLof 0.1Nsodium hydroxide with freshly boiled and cooled purified water to 200mL.
Mercuric Bromide Test Paper —Use alcoholic mercuric bromide TS.Store protected from light.
Methyl Yellow Paper —Use a 1in 2000solution of methyl yellow in alcohol.
pH Indicator Paper,Short-Range —Use a suitable grade.
Phenolphthalein Paper —Use a 1in 1000solution of phenolphthalein in diluted alcohol.
Starch Iodate Paper —Use a mixture of equal volumes of starch TSand potassium iodate solution (1in 20).
Starch Iodide Paper —Use a solution of 500mg of potassium iodide in 100mLof freshly prepared starch TS.
Thiazole Yellow Paper— Use a 1in 2000solution of thiazole yellow in water.
Turmeric Paper —Use a solution prepared as follows:Macerate 20g of powdered turmeric,the dried root of Curcuma longaLinné(Fam.Zingiberaceae),with four 100-mLportions of cold water,decanting the clear liquid portion each time and discarding it.Dry the residue at a temperature not over 100.Macerate with 100mLof alcohol for several days,and filter.
Sensitiveness —Dip a strip of the paper,of about 1.5-cm length,in a solution of 1.0mg of boric acid in 5mLof water,previously mixed with 1mLof hydrochloric acid.After 1minute remove the paper from the liquid,and allow it to dry:the yellow color changes to brown.Then moisten the paper with ammonia TS:the color of the paper changes to greenish black.