Indicators
In the test and assays of the pharmaceutical ingredients, indicators are required to indicate the completion of a chemical reaction in volumetric analysis or to indicate the pH of solutions. Indicators may be substituted for one another provided the colors change over approximately the same range of pH but in the event of doubt or dispute as to the equivalence of indicators for a particular procedure, the indicator specified in the individual monograph is alone authoritative.
Any solvent required in a determination or test in which an indicator is specified should be previously neutralized to the indicator unless a blank determination is performed or specified.
Given below are materials which are to be used as indicators and the manner in which solutions of indicators are to be prepared.
Table 1 lists the more commonly used pH indicators in ascending order of the lower limit of their range with the corresponding color changes.
Alizarin Red S; CI 58005; Alizarin S; Mordant Red B; Sodium Alizarine Sulphonate; 9,l0-dihydro- 3,4-dihydroxy-9, l0-dioxo2- anthrancesulphonic Acid Monosodium salt:
C14H7NaO7S.H20 = 360.27
General laboratory reagent grade of commerce.
Yellowish brown or orange-yellow powder.
Alizarin Red S Indicator Solution; Alizarin S Indicator Solution:
A 0.1 percent w/v solution of alizarin red S. Complies with the following test.
SENSITIVITY TO BARIUM - To 5 ml of 0.05 M sulphuric acid add 5 ml of water, 50 ml of acetate buffer pH 3.7 and 0.5 ml of the solution under examination. Add, dropwise, 0.05 M barium perchlorate; the color changes from yellow to orange-red.
Azo Violet; Magneson; 4-(p-Nitrophenylazo)resorcinol Indicator:
C12H9N304=259.22
Red powder; mp, about 1930, with decomposition.
Brilliant Green; CI 42040; Malachite Green G; Basic Green 1 Indicator:
C27H34N2O4S=482.64
Technical Grade of commerce.
Small, glistening golden crystals.
Brilliant Green Solution:
A 0.5 per cent w/v solution of brilliant green in glacial acetic acid.Bromocresol Green; Bromocresol Blue; 4,4-(3H-2,1Benzoxathiol-3-ylidene)bis(2,6-dibromo-m-cresol) S,S-dioxide Indicator:
C21HI4Br4O5S= 698.01
White or pale buff-coloured powder.
Bromocresol Green Reagent Indicator:
Prepare a phosphate buffer solution by dissolving 43.0 g of sodium dihydrogen phosphate and 2.0 g of anhydrous sodium phosphate in sufficient water to make 1000 ml. Dissolve 0.2 g of bromocresol green in 30 ml of water and 6.5 ml of 0.1 M sodium hydroxide. Dilute to 500 ml with the phosphate buffer solution, mix and adjust the pH to 4.6 with 0.1 M hydrochloric acid.Bromocresol Green Indicator Solution:
Dissolve 50 mg of bromocresol green in 0.72 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 percent). After the solution is effected, add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY - A mixture of 0.2 ml of the solution and 100 ml of carbon dioxide-free water is blue. Not more than 0.2 ml of 0.02 M hydrochloric acid is required to change the color of the solution to yellow.
Bromocresol Purple Indicator; 4,4' -(3H-2, 1-Benzoxathiol-3-ylidene)bis(6-bromo-o-cresol) S,S-dioxide: C2IH16Br2O5S= 540.23
White to pink, crystalline powder.
Bromocresol Purple Indicator Solution:
Dissolve 50 mg of bromocresol purple in 0.92 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 percent). After the solution is effected, add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY - A mixture of 0.2 ml of the solution and 100 ml of carbon dioxide-free water to which 0.05 ml of 0.02 M sodium hydroxide has been added is bluish violet. Not more than 0.2 ml of 0.02 M hydrochloric acid is required to change the color to yellow.
Bromocresol Purple Indicator Solution, Phosphate-buffered:
Dissolve 43 g of potassium dihydrogen phosphate and 5 g of sodium phosphate in water to make 1000 ml. Adjust the pH of the solution to 5.3 ± 0.1, if necessary (Solution A). Dissolve 0.4 g of bromocresol purple in 30 ml of water, add 6.3 ml of 0.1 M sodium hydroxide and dilute with water to make 500 ml (Solution B). Shake equal volumes of solution A, solution B and chloroform in a separator, allow the layers to separate and discard the chloroform. If the appreciable color is extracted by the chloroform, repeat with additional quantities of chloroform until no further color is extracted.Bromophenol Blue Indicator; 4,4' -(3H- 2,1- Benzoxathiol- 3-ylidene)bis(2,6-dibromophenol) S,S-dioxide: C19H10Br4O5S= 669.96
Pinkish crystals.
Bromophenol Blue Indicator Solution; Strong Bromophenol Blue Indicator Solution; Ethanolic Bromophenol Blue Indicator Solution:
Dissolve 0.1 g of bromophenol blue with gentle heating in 1.5 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 percent) and add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY- A mixture of 0.05 ml of the solution and 20 ml of carbon dioxide-free water to which 0.05 ml of 0.1 M hydrochloric acid has been added is yellow. Not more than 0.1 ml of 0.1 M sodium hydroxide is required to change the color to bluish violet.
Bromophenol Blue Reagent Indicator:
Dissolve 50 mg of bromophenol blue with gentle heating in 3.73 ml of 0.02 M sodium hydroxide and dilute to 100 ml with water.Bromothymol Blue Indicator; 4,4' -(3H-2, I-Benzoxathiol-3-ylidene)bis(2-bromothymol) S,S-dioxide:
C27H28Br2O5S=624.39.
Cream-coloured powder.
Bromothymol Blue Indicator Solution; Aqueous Bromothymol Blue Indicator Solution:
Dissolve 50 mg of bromothymol blue in 4 ml of 0.02 M sodium hydroxide and 20 ml of ethanol (95 percent). After the solution is effected, add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY - A mixture of 0.3 ml of the solution and 100 ml of carbon dioxide-free water is yellow. Not more than 0.1 ml of 0.02 M sodium hydroxide is required to change the color to blue.
Calcon Indicator; CI 15705; SolochromeDarkBlue; Mordant Black 17; Sodium 2-hydroxy-l-(2-hydroxy-I-naphthylazo )-naphthalene4- sulphonate:
C20H13N2NaO5S=416.38
General laboratory reagent grade of commerce.
Brownish black powder with a violet sheen. Gives a purple-red color with calcium ions in alkaline solution. When metal ions are absent, for example, in the presence of an excess of disodium edetate, the solution is blue.
Calcon Indicator Mixture:
A mixture of 1 part of calcon with 99 parts of freshly ignited anhydrous sodium sulphate.
Complies with the following test.
SENSITIVITY – Dissolve 0.l gin 2.5 ml of water. To l ml of the solution add 50 ml of water, 10 ml of 1 M sodium hydroxide and 1 ml of a 1 percent w/v solution of magnesium sulfate; the solution is blue. Add 0.1 ml of a 0.15 percent w/v solution of calcium chloride; the solution becomes violet and on subsequent addition of 0.1 ml of 0.01 M disodium edentate turns to blue again.
Congo Red Indicator; CI 22120; Disodium (4,4' -bipheny Ibis- 2,2-azo) bis(1-amlnonaphthalene-4-sulphonate):
C32H22N6Na2O6S2= 696.66
Dark red or reddish brown powder. Decomposes on exposure to acid fumes.
Congo Red Fibrin Indicator:
Soak washed and shredded fibrin overnight in a 2 percent w/v solution of congo red in ethanol (90 percent), strain, wash the product with water and store under ether.Cresol Red Indicator; 4,4' -(3H-2, 1-Benzoxathiol- 3-ylidene) di-o-cresol S,S-dioxide:
C21HI8O5S=382.44
Red brown powder.
Cresol Red Indicator Solution:
Warm 0.1 g of cresol red in a mixture of 2.65 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 percent). After the solution is effected, add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY - A mixture of 0.1 ml of the solution and 100 ml of carbon dioxide-free water to which 0.15 ml of 0.02 M sodium hydroxide has been added is purplish red. Not more than 0.1 5 ml of 0.02 M hydrochloric acid is required to change the color to yellow.
Crystal Violet Indicator; CI 42555; Basic Violet 3; Hexamethylp-rosaniline Chloride:
C25H30CIN3= 407.98
When used for titrations in non-aqueous media, changes from violet (basic) through blue-green (neutral) to yellowish green (acidic).
Crystal Violet Indicator Solution:
A 0.5 percent w/v solution of crystal violet in anhydrous glacial acetic acid.
Complies with the following test.
SENSITIVITY - A mixture of 0.1 ml of the solution and 50 ml of anhydrous glacial acetic acid is bluish purple. Add 0.1 ml of 0.1 M perchloric acid; the solution turns blue-green.
Dimethyl Yellow Indicator; CI 11020; 4-Dimethylamlnoazobenzene:
CI4HI5N3= 225.29
Yellow crystalline leaflets; mp, about I16°.
Complies with the following test.
HOMOGENEITY - Carry out the method for thin-layer chromatography, using silica gel G as the coating substance and dichloromethane as the mobile phase. Apply to the plate 10 µl of a 0.01 percent w/v solution in dichloromethane.
The chromatogram shows only one spot.
Dimethyl Yellow Indicator Solution:
A 0.2 percent w/v solution of dimethyl yellow in ethanol (90 percent).
Complies with the following test.
SENSITIVITY - A solution containing 2 g of ammonium chloride in 25 ml of carbon dioxide-free water, to which is added 0.1 ml of the dimethyl yellow solution, is yellow. Not more than 0.1 ml of 0.1 M hydrochloric acid is required to change the color to red.
Dimethyl Yellow-Oracet Blue B Indicator Solution; Dimethyl Yellow Solvent Blue 19 Indicator Solution:
Dissolve 15 mg of dimethyl yellow and 15 mg of oracet blue B in chloroform and dilute to 500 ml with chloroform.
Eosin; CI 45380; Acid red 87: C20H6Br4Na2O5= 691.86
General laboratory reagent grade of commerce.
Red powder.
Eosin Indicator Solution:
A 0.5 percent w/v solution of eosin in water.Eriochrome Black T Indicator; CI 14645; Mordant Black 11;Solochrome Black; Sodium 1-(l-hydroxy-2-naphthylazo )-5-nitro-2-naphthol-4-sulphonate:
C20HI2N3NaO7S= 461.38
General laboratory reagent grade of commerce.
Brownish black powder having a faint, metallic sheen. Gives a red colour with calcium, magnesium, zinc and certain other metals in alkaline solutions. When metal ions are absent, for example in the presence of an excess of disodium edetate, the solution is blue.
Store protected from light and moisture.
Complies with the following test.
SENSITIVITY - To 10 ml of a 1 in 200,000 solutions in a mixture of equal parts of methanol and water add a 1 percent w/v solution of sodium hydroxide until the pH is 10; the solution is pure blue in color and free from cloudiness. Add 0.01 ml of 0.05 M magnesium sulphate; the color of the solution changes to red-violet, and on adding more 0.05 M magnesium sulphate, the solution becomes wine-red in color.
Eriochrome Black T Indicator Mixture; Eriochrome Black T Triturate; Mordant Black 11 Mixture:
A mixture of 1 part of eriochrome black T and 99 parts of sodium chloride.
Store protected from light and moisture.
Complies with the following test.
SENSITIVITY - Dissolve 50 mg in 100 ml of water, a brownish violet color is produced. Add 0.3 ml of 6 M ammonia; the color changes to blue. Add 0.1 ml of a 1 percent w/v solution of magnesium sulphate; the color changes to violet.
Eriochrome Black T Indicator Solution; Mordant Black II Indicator Solution:
Dissolve 0.2 g of eriochrome black T and 2 g of hydroxylamine hydrochloride in sufficient methanol to produce 50 ml.
Prepare immediately before use.
Fast Blue B Salt Indicator; CI 37235:
CI4Hl2Cl2N4O2= 339.18
General laboratory reagent grade of commerce.
Dark green powder, stabilised by the addition of zinc chloride.
Store protected from moisture in a cold place.
Ferroin Indicator Solution; Ferroin Sulphate Solution; Tris-(l, 10-phenanthroline) ferrous Sulphate Complex:
Dissolve 0.7 g of ferrous sulphate and 1.5 g of 1,1 O-phenanthroline hydrochloride in 70 ml of water and add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY - Add 0.1 ml of the solution and 0.15 ml of osmic acid solution to 50ml of 1M sulphuric acid. Add 0.1 ml of 0.1 M eerie ammonium nitrate; the color changes from red to light blue.
Indophenol Blue Indicator; CI49700:
CI8H26N2O=276.34
General laboratory reagent grade of commerce.
Dark purple powder.
Complies with the following test.
HOMOGENEITY - Carry out the method for thin-layer chromatography (2.4.17), using silica gel G as the coating substance and dichloromethane as the mobile phase. Apply to the plate 10 /11 of a 0.0 I percent w/v solution in dichloromethane. After removal of the plate, allow it to dry in air. The chromatogram shows only one spot, but a stain may remain at the point of origin.
Litmus:
Fragments of blue pigment prepared from various species of Rocella, Lecanora or other lichens. It has a characteristic odor. Partly soluble in water and in ethanol.
NOTE - Litmus is unsuitable for determining the pH of alkaloids, carbonates and bicarbonates.
Litmus Indicator Solution:
Boil 25 g of coarsely powdered litmus with 100 ml of ethanol (90 percent) under a reflux condenser for 1 hour and discard the clear liquid. Repeat this operation with two quantities, each of 75 ml of ethanol (90 percent). Digest the extracted litmus with 250 ml of water and filter.Metacresol Purple Indicator; 4,4' -(3H-2, I-Benzoxanthiol-3-ylidene)-dim- cresol S,S-dioxide:
C21H16O5S= 380.40
General laboratory reagent grade of commerce.
Metalphthalein; Phthalein Purple Indicator:
C32H32N2O12+aq
Creamy white brown powder.
Complies with the following test.
SENSITIVITY - Dissolve 10 mg in 1 ml of strong ammonia solution and dilute to l0ml with water. To 5 ml of the solution add 95 ml of water, 4 ml of strong ammonia solution, 50 ml of ethanol (95 percent) and 0.2 ml of 0.1 M barium chloride; the solution is bluish violet. Add 0.24 ml of 0.05 M disodium edetate; the solution becomes colorless.
Metanil Yellow Indicator; CI 13065; Sodium 4-anilinoazobenzene-3-sulphonate:
C18H14N3NaO3S = 375.40
Brownish yellow powder; soluble in water and in ethanol; slightly soluble in acetone and in ether.
Metanil Yellow Indicator Solution:
A 0.1 percent w/v solution of metanil yellow in methanol.
Complies with the following test.
SENSITIVITY - Add 0.1 ml of the solution to 50 ml of anhydrous glacial acetic acid; the mixture is pinkish red.
Add 0.05 ml of 0.1 M perchloric acid; the color changes to violet.
Methyl Orange Indicator
C14H14N3NaO3S = 327.34
Orange-yellow powder or crystalline scales; Sparingly soluble in hot water; slightly soluble in water; practically insoluble in ethanol.
Methyl Orange Indicator Solution:
Dissolve 0.1 g of methyl orange in 80 ml of water and add sufficient ethanol (95 percent) to produce l00 ml.
Complies with the following test.
SENSITIVITY - A mixture of 0.1 m] of the solution and 100 ml of carbon dioxide-free water is yellow. Not more than 0.1 ml of 0.1 M hydrochloric acid is required to change the color to red.
Methyl Red Indicator; CI 13020; 2-(4-Dimethylarninophenylazo )-benzoic Acid:
C15H15N3O2=269.30
Dark red powder or violet crystals; mp, about 182°; soluble in ethanol; practically insoluble in water.
Methyl Red- Methylene Blue Indicator Solution; Methyl Red Mixed Indicator Solution:
Dissolve 0.1 g of methyl red and 50 mg of methylene blue in 100 ml of ethanol (95 percent). Color changes from reddish violet to green (pH range, 5.2 to 5.6).Methyl Red Indicator Solution:
Dissolve 50 mg of methyl red in a mixture of 1.86 ml of 0.1 M sodium hydroxide and 50 ml of ethanol (95 percent). After the solution is effected, add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY - A mixture of 0.1 ml of the solution, 100 ml of carbon dioxide-free water and 0.05 ml of 0.02 M hydrochloric acid is red. Not more than 0.1 ml of 0.02 M sodium hydroxide is required to change the color to yellow.
Methylenebisacrylamlde Indicator:
C7H10N2O2 = 154.2
A fine, white or almost white powder, slightly soluble in water, soluble in alcohol.
mp. it melts with decomposition at a temperature above 300°.
Methylene Blue Indicator; CI 52015; Basic Blue 9; 3,7-Bis-(dimethylamlno)phenothiazin- 5-ium chloride:
C16H18CIN3S.xH20 = 319.86 (anhydrous)
Redox indicator grade suitable for biological work.
Dark green or brown crystals with bronze lustre or crystalline powder; hygroscopic; soluble in water and in chloroform; sparingly soluble in ethanol; insoluble in ether.
Methylene Blue Indicator Solution:
Dissolve 150 mg of methylene blue in 100 ml of ethanol (95 percent) and dilute with ethanol (95 percent) to produce 250 ml.Methyl Orange-Xylene Cyanol FF Indicator Solution:
Dissolve 0.1 g of methyl orange and 0.26 g of xylene cyanol FF in 50 ml of ethanol (95 percent) and add sufficient water to produce l00ml.Methyl Thymol Blue Indicator; [3H-2,1-Benzoxathiol-3-ylidenebis(6-hydroxy- 5-isopropyl- 2-methyl-m-phenylene) methy lenenitrilo]tetraacetic acid S, S-dioxide Tetrasodium salt:
C37H40N2Na4O13S = 844.75
General laboratory reagent grade of commerce.
Produces a blue color with calcium ions in alkaline solution. When metal ions are absent, for example, in the presence of an excess of disodium edetate, the solution is grey.
1-Naphtholbenzein; a-Naphtholphthalein; Phenylbis-(4hydroxynaphthyl) methanol:
C27H20O3 = 392.50Brownish red powder or shiny brownish black crystals. 1-Naphtholbenzein Solution; a-Naphtholbenzein Indicator Solution:
A 0.2 percent w/v solution of 1-naphtholbenzein in anhydrous glacial acetic acid.
Complies with the following test.
SENSITIVITY - Add 0.25 ml to 50 ml of anhydrous glacial acetic acid. Not more than 0.05 ml of 0.1 M perchloric acid is required to change the color of the solution from brownish yellow to green.
Neutral Red Indicator; CI 50040; Basic Red 5; 3-Amlno-7-dimethylamlno2-methylphenazine Monohydrochloride:
C15Hl6N4.HCI = 288.78
Reddish to olive green coarse powder; sparingly soluble in ethanol and in water.
Neutral Red Indicator Solution:
A 0.1 percent w/v solution of neutral red in ethanol (50 percent).Nile Blue A Indicator; CI 51180; 5-Amlno-9-diethylamlnobenzo[ a]phenoxazinylium Hydrogen Sulphate:
C20H21N3O5S=415.47
Green,crystalline powder with a bronze lustre.
Complies with the following test.
LIGHT ABSORPTION - A 0.0005 per cent w/v solution in ethanol (50 per cent) exhibits a maximum at about 640 nm.
Nile Blue A Indicator Solution:
A 1 per cent w/v solution of nile blue A in anhydrous glacial acetic acid.
Complies with the following test.
SENSITIVITY - A solution containing 0.25 ml in 50 ml of anhydrous glacial acetic acid is blue. Not more than 0.1 ml of 0.1 M perchloric acid is required to change the color of the solution to bluish green.
Colour changes from blue to red (pH range, 9.0 to 13.0).
Oracet Blue B Indicator; Solvent Blue 19 Indicator:
A mlxture of 1-methylamlno4-anilinoanthraquinone, C21H16N2O2, and l-amlno-4anilinoanthraq uinone, C20H14N2O2.
When used for titration in non-aqueous media, it changes from blue (basic) through purple (neutral) to pink (acidic).
Oracet Blue B Indicator Solution:
A 0.5 per cent w/v solution of oracet blue B in anhydrous glacial acetic acid.Phenol Red Indicator; Phenolsulphonphthalein; 4,4' -(3H-2,1Benzoxathiol-3-ylidene )diphenol S,S-dioxide:
C19HI4O5S= 354.39
Bright to dark red crystalline powder; freely soluble in solutions of alkali carbonates and hydroxides; slightly soluble in ethanol (95 percent); very slightly soluble in water.
Phenol Red Indicator Solution:
Dissolve 0.1 g of phenol red in 2.82 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 percent). After the solution is effected, add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY - A mixture of 0.1 ml of the solution and 100 ml of carbon dioxide-free water is yellow. Not more than 0.1 ml of 0.02 M sodium hydroxide is required to change the color of the solution to reddish violet.
Phenol Red Reagent Indicator:
SOLUTION I - Dissolve 33 mg of phenol red in 1.5 ml of 2 M sodium hydroxide and dilute to 100 ml with water.
SOLUTION n - Dissolve 25 mg of ammonium sulphate in 235 ml of water, add 105 ml of 2 M sodium hydroxide and 135 ml of 2 M acetic acid.
Add 25 ml of solution I to solution II. If necessary, adjust the pH of the mixture to 4.7.
Phenolphthalein Indicator:
Of the Indian Pharmacopoeia.Phenolphthalein Indicator Solution:
A 1.0 percent w/v solution of phenolphthalein in ethanol (95 percent).Phenolphthalein Indicator Solution, Dilute:
Dissolve 0.1 g of phenolphthalein in 80 ml of ethanol (95 percent) and add sufficient water to produce 100 ml. Complies with the following test.
SENSITIVITY - A mixture of 0.1 ml of the solution and 100 ml of carbon dioxide-free water is colorless. Not more than 0.2 ml of 0.02 M sodium hydroxide is required to change the color to pink.
Phenolphthalein-Thymol Blue Indicator Solution:
Dissolve 0.1 g of thymol blue in a mixture of 2.2 ml of 0.1 M sodium hydroxide and 50 ml of ethanol (95 percent) and dilute to 100 ml with water. Mix 3 volumes of this solution with 2 volumes of phenolphthalein solution.Pyridylazonaphthol; PAN; 1-(2-Pyridylazo )-2-naphthol:
C15H11N3O= 249.27
General laboratory reagent grade of commerce.
Brick red or orange-red powder; mp, about 1400.
Pyridylazonaphthol Indicator Solution:
A 0.1 per cent w/v solution in ethanol.
Complies with the following test.
SENSITIVITY - To 50 ml of water add 10 ml of acetate buffer pH 4.4,0.1 ml of 0.02 M disodium edetate and 0.25 ml of the reagent under examination; a yellow color is produced. Add 0.15 ml of a 0.5 percent w/v solution of cupric sulphate; the color changes to violet.
Quinaldine Red Indicator; 2-(4-Dimethylamlnostyryl) quinoline Ethiodide:
C21H23IN2= 430.33
When used for the non-aqueous titration in anhydrous glacial acetic acid, the color changes from magenta (basic) to almost colorless (acidic).
Quinaldine Red Indicator Solution:
A 0.1 percent w/v solution of quinaldine red in methanol.Ruthenium Red Indicator; Ammoniated Ruthenium Oxychloride:
H12Cl2N1402Ru3,4H20 = 858.42
Microscopical staining grade of commerce.
Brownish red powder.
Ruthenium Red Indicator Solution:
Dissolve 8 mg of ruthenium red in
10 ml of lead acetate solution.
Sudan Red G Indicator; CI 12150; Sudan
C17HI4N4O=290.32
Complies with the following test.
HOMOGENEITY - Carry out the method for thin-layer chromatography, using silica gel G as the coating substance and dichloromethane as the mobile phase but allowing the solvent front to ascend 10 cm above the line of application. Apply to the plate 10 full of a 0.1 percent w/v solution in dichloromethane. After removal of the plate, allow it to dry in air. The chromatogram shows only one spot.
Thymol Blue Indicator; Thymolsulphonphthalein; 4,4' -(3H)-2, 1Benzoxathiol-3-ylidene) dithymol S,S-dioxide:
C27H30O5S =466.60
Brownish green, crystalline powder; soluble in ethanol (95 percent) and in dilute alkali solutions; slightly soluble in water.
Thymol Blue Indicator Solution:
Dissolve 0.1 g of thymol blue in 2.15 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 percent). After the solution is effected, add sufficient water to produce 100 ml.
Complies with the following test.
SENSITIVITY - A mixture of 0.1 ml of the solution and 100 ml of carbon dioxide-free water to which 0.2 ml of 0.02 M sodium hydroxide has been added is blue. Not more than 0.1 ml of 0.02 M hydrochloric acid is required to change the color to yellow.
Thymol Blue Indicator Solution, Ethanolic:
Dissolve 0.1 g of thymol blue in 100 ml of ethanol (95 percent) and filter, if necessary.Thymolphthalein Indicator; 3,3-Bis( 4-hydroxy-5-isopropyl- 2mehtylphenyl)phthalide:
C28H30O4=430.55
White to slightly yellow crystalline powder; soluble in ethanol (95 percent) and in solutions of alkali hydroxides; insoluble in water.
Thymolphthalein Indicator Solution:
A 0.1 percent w/v solution of thymolphthalein in ethanol (95 percent).
Complies with the following test.
SENSITIVITY - A mixture of 0.05 ml and 100 ml of carbon dioxide-free water is colorless. Not more than 0.05 ml of 0.1 M sodium hydroxide is required to change the color to blue.
Titan Yellow Indicator; CI 19540; Thiazol Yellow; Sodium 2,2[(diazoamlno )di-p-phenylene] bis(6-methylbenzothiazole-7sulphonate):
C28HI9N5Na2O6S4= 695.71
Yellowish brown powder.
Titan Yellow Indicator Solution:
A 0.05 percent w/v solution of titan yellow. Complies with the following test.
SENSITIVITY - Add 0.1 ml to a mixture of 10 ml of water, 0.2 ml of a 0.0101 percent w/v solution of magnesium sulphate and 1.0 ml of 1M sodium hydroxide; a pink color is produced.
Xylene Cyanol FF Indicator:
C142135
Blue, ethanol-soluble dye used as a screening agent in methyl orange-xylene cyanol FF solution.
Xylenol Orange Indicator; [3H-2,1-Benzoxathiol-3-ylidenebis-(6-hydroxy- 5-methyl-m-phenylene )methylenenitrilo ]tetra acetic acid S,S-dioxide Tetrasodium Salt:
C3IH28N2NH2OI3S=760.60
General laboratory reagent grade of commerce.
Reddish brown, crystalline powder; gives a violet color with mercury, lead, zinc and certain other metal ions, in alkaline solutions. When metal ions are absent, for example in the presence of an excess of disodium edetate, the solution is yellow.
XylenolOrange Mixture Indicator; Xylenol Orange Triturate Indicator:
Triturate 1 part of xylenol orange with 99 parts of potassium nitrate.
Complies with the following test.
SENSITIVITY - Add 50 mg to a mixture of 50 ml of water, 1 ml of 2 M acetic acid and 0.05 ml of lead nitrate solution. Add sufficient hexamine to change the color from yellow to violet red. Add 0.1 ml of 0.1 M disodium edetate; the color changes to yellow.
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