Preparation of Indicator Solutions

Preparation of Indicator Solutions

Indicators

In the test and
assays of the Pharmacopoeia, indicators are required to indicate the completion
of a chemlcal reaction in volumetric analysis or to
indicate the pH of solutions. Indicators may be substituted for one another
provided the colours 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 determlnation or test in which an
indicator is specified should be previously neutralized to the indicator unless
a blank determlnation 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 limlt of their range with the corresponding colour changes.

Alizarin Red S; CI 58005; Alizarin S; MordantRedB;
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 Solution; Alizarin S Solution:
A0.1 per cent 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 examlnation. Add, dropwise,
0.05 M barium perchlorate; the colour changes from yellow to orange-red.

Azo Violet; Magneson;
4-(p-Nitrophenylazo)resorcinol:

C12H9N304=259.22

Red
powder; mp, about 1930, with decomposition.

Brilliant Green; CI 42040; Malachite Green G; Basic Green 1:

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:

C₂₁H_I4Br₄O₅S=
698.01

White
or pale buff-coloured powder.

 

Bromocresol Green Reagent:
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, mlx and adjust the pH to 4.6 with 0.1
M hydrochloric acid.

Bromocresol Green Solution:
Dissolve 50 mg of bromocresol green in
0.72 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 per
cent). After solution is effected, add sufficient
water to produce 100 ml.

Complies
with the following test.

SENSITIVITY - A mlxture of 0.2 ml of the sol ution 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 colour of the solution to yellow.

Bromocresol Purple; 4,4'
-(3H-2, 1-Benzoxathiol-3-ylidene)bis(6-bromo-o-cresol)
S,S-dioxide: C_2IH₁₆Br₂O₅S=
540.23

White
to pink, crystalline powder.

Bromocresol Purple Solution:
Dissolve 50 mg of bromocresol purple in
0.92 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 per
cent). After solution is effected, add sufficient
water to produce 100 ml.

Complies
with the following test.

SENSITIVITY - A mlxture 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 colour to yellow.

Bromocresol Purple 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
appreciable colour is extracted by the chloroform,
repeat with additional quantities of chloroform until no further colour is extracted.

Bromophenol Blue; 4,4'
-(3H- 2,1- Benzoxathiol- 3-ylidene)bis(2,6-dibromophenol) S,S-dioxide:
C₁₉H₁₀Br₄O₅S= 669.96

Pinkish
crystals.

Bromophenol Blue Solution; Strong Bromophenol Blue Solution; Ethanolic
Bromophenol Blue Solution:
Dissovle 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 per cent) and add sufficient water to
produce 100 ml.

Complies
with the following test.

SENSITIVITY- A mlxture 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 colour to bluish violet.

Bromophenol Blue Reagent:
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; 4,4'
-(3H-2, I-Benzoxathiol-3-ylidene)bis(

2-bromothymol) S,S-dioxide:
C₂₇H₂₈Br₂O₅S=624.39.

Crearn-coloured
powder.

Bromothymol Blue Solution; Aqueous Bromothymol Blue Solution:
Dissolve 50 mg of bromothymol blue in 4
ml of 0.02 M sodium
hydroxide and 20 ml of ethanol (95 per cent). After solution is effected,
add sufficient water to produce 100 ml.

Complies
with the following test.

SENSITIVITY - A mlxture 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 colour to blue.

Calcon; 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 purplered colour 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 Mlxture:
A mlxture 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 per cent w/v solution
of magnesium sulphate; the solution is blue.
Add 0.1 ml of a 0.15 per cent 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; 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:
Soak washed and shredded fibrin ovemlght in a
2 per cent w/v solution of congo red in
ethanol (90 per cent), strain, wash the product with water and
store under ether.

Cresol Red; 4,4' -(3H-2, 1-Benzoxathiol-
3-ylidene) di-o-cresol S,S-dioxide:
C₂₁H_I8O₅S=382.44

Red
brown powder.

Cresol Red Solution: Warm 0.1 g of cresol
red in a mlxture of 2.65 ml of 0.1 M sodium
hydroxide and 20 ml of ethanol (95 per cent). After solution
is effected, add sufficient water to produce
100 ml.

Complies
with the following test.

SENSITIVITY - A mlxture 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 colour to yellow.

Crystal Violet; 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 Solution: A 0.5 per cent
w/v solution of crystal violet in anhydrous glacial acetic acid.

Complies
with the following test.

SENSITIVITY - A mlxture 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; CI 11020;
4-Dimethylamlnoazobenzene: C_I4H_I5N₃=
225.29

Yellow
crystalline leaflets; mp, about I16°.

Complies
with the following test.

HOMOGENEITY -
Carry out the method for thin-layer chromatorgraphy,
using silica gel G as the coating susbtance
and dichloromethane as the mobile phase. Apply to the plate 10 µl
of a 0.01 per cent w/v solution in dichloromethane.

The
chromatogram shows only one spot.

Dimethyl Yellow Solution:
A 0.2 per cent w/v solution of dimethyl
yellow in ethanol (90 per cent).

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 colour to red.

Dimethyl Yellow-Oracet
Blue B Solution; Dimethyl YellowSolvent
Blue 19 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 Solution: A 0.5 per cent w/v
solution of eosin in water.

Eriochrome Black T; CI 14645; Mordant Black
11;SolochromeBlack; Sodium 1-(l-hydroxy-2-naphthylazo
)-5-nitro-2naphthol-4-sulphonate: C₂₀H_I2N₃NaO₇S=
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 solution in a mlxture of equal parts of methanol and water add
a 1 per cent w/v solution of sodium hydroxide until the pH is 10; the
solution is pure blue in colour and free from
cloudiness. Add 0.01 ml of 0.05 M magnesium sulphate;
the colour of the solution changes to red-violet,
and on adding more 0.05 M magnesium sulphate,
the solution becomes wine-red in colour.

Eriochrome Black T Mlxture;
Eriochrome Black T Triturate; Mordant Black 11 Mlxture: A mlxture 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 ] 00 ml of water, a brownish
violet colour is produced. Add 0.3 ml of 6 M
ammonia; the colour changes to blue. Add 0.1 ml
of a 1 per cent w/v solution of magnesium sulphate;
the colour changes to violet.

Eriochrome Black T Solution; Mordant Black
11 Soluton:

Dissolve 0.2 g
of eriochrome black T and 2 g of hydroxylamlne hydrochloride in sufficient methanol
to produce 50 m\.

Prepare
immediately before use.

Fast Blue B Salt; CI 37235:
C_I4H_l2Cl₂N₄O₂= 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 Solution; Ferroin
Sulphate Solution; Tris-(l,
10phenanthroline) 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 osmlc
acid solution to 50 ml of 1 M sulphuric acid. Add
0.1 ml of 0.1 M eerie ammonium nitrate; the colour
changes from red to light blue.

Indophenol Blue; CI49700:
C_I8H₂₆N₂O=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 per cent 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 odour. Partly soluble in water and
in ethanol.

NOTE
- Litmus is unsuitable for determlning
the pH of alkaloids, carbonates and bicarbonates.

Litmus Solution: Boil 25 g of
coarsely powdered litmus with 100 ml of ethanol (90 per cent) 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 per cent). Digest
the extracted litmus with 250 ml of water and filter.

Metacresol Purple; 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: 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 lOaml with water. To 5 ml of the solution add
95 ml of water, 4 ml of strong ammonia solution, 50 ml of
ethanol (95 per cent) 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 colourless.

Metanil Yellow; CI 13065; Sodium
4-anilinoazobenzene-3sulphonate:

C₁₈H₁₄N₃NaO₃S
= 375.40

Brownish yellow
powder; soluble in water and in ethanol; slightly soluble in acetone
and in ether.

Metanil Yellow Solution:
A 0.1 per cent 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
mlxture is pinkish red.

Add 0.05 ml of 0.1
M perchloric acid; the colour
changes to violet.

Methyl Orange; CI 13025; Sodium 4-dimethylamlnoazobenzene-
4-sulphonate: C₁₄H₁₄N₃NaO₃S
= 327.34

Orange-yellow
powder or crystalline scales; Sparingly soluble in hot
water; slightly soluble in water; practically insoluble in ethanol.

Methyl Orange Solution: Dissolve 0.1 g
of methyl orange in 80 ml of water and add sufficient ethanol (95
per cent) to produce l00 ml.

Complies
with the following test.

SENSITIVITY - A mlxture 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 colour to red.

Methyl Red; 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
Solution; Methyl Red Mlxed Solution:
Dissolve 0.1 g of methyl red and 50 mg of methylene blue in 100 ml of ethanol (95
per cent). Colour changes from reddish violet to green (pH range, 5.2
to 5.6).

Methyl Red Solution: Dissolve 50 mg of methyl
red in a mlxture of 1.86 ml of 0.1 M sodium
hydroxide and 50 ml of ethanol (95 per cent). After solution
is effected, add sufficient water to produce
100 ml.

Complies
with the following test.

SENSITIVITY - A mlxture 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 colour to
yellow.

Methylenebisacrylamlde:
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; 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 Solution:
Dissolve 150 mg of methylene blue in
100 ml of ethanol (95 per cent) and dilute with ethanol (95
per cent) to produce 250 ml.

Methyl Orange-Xylene Cyanol FF Solution: Dissolve 0.1 g of methyl
orange and 0.26 g of xylene cyanol FF in 50 ml of ethanol (95 per cent) and
add sufficient water to produce l00ml.

Methyl Thymol Blue; [3H-2,1-Benzoxathiol-3-ylidenebis(6-hydroxy- 5-isopropyl-
2-methyl-m-pheny lene) methy
lenenitrilo]tetraacetic
acid S, S-dioxide Tetrasodium salt:

C₃₇H₄₀N₂Na₄O₁₃S
= 844.75

General
laboratory reagent grade of commerce.

Produces
a blue colour 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)methenol:C₂₇H₂₀O₃
= 392.50

Brownish red powder or shiny
brownish black crystals.
1-Naphtholbenzein Solution; a-Naphtholbenzein
Solution: A 0.2 per cent 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 colour of the solution from brownish
yellow to green.

Neutral Red; CI 50040; Basic Red 5;
3-Amlno-7-dimethylamlno2-methylphenazine Monohydrochloride:
C₁₅H_l6N₄.HCI = 288.78

Reddish to
olive green coarse powder; sparingly soluble in ethanol and in water.

Neutral Red Solution: A 0.1 per cent w/v
solution of neutral red in ethanol (50 per cent).

Nile Blue A; 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
ABSORBTION - A 0.0005 per cent w/v solution in ethanol (50 per cent) exhibits
a maximum at about 640 nm.

Nile Blue A 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 colour of the
solution to bluish green.

Colour
changes from blue to red (pH range, 9.0 to 13.0).

Oracet Blue B; Solvent Blue 19:
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 Solution:
A 0.5 per cent w/v solution of oracet blue
B in anhydrous glacial acetic acid.

Phenol Red; Phenolsulphonphthalein;
4,4' -(3H-2,1Benzoxathiol-3-ylidene )diphenol S,S-dioxide:

C₁₉H_I4O₅S=
354.39

Bright to dark
red crystalline powder; freely soluble in solutions of alkali carbonates and
hydroxides; slightly soluble in ethanol (95 per cent); very
slightly soluble in water.

Phenol Red Solution: Dissolve 0.1 g of phenol
red in 2.82 ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95
per cent). After solution is effected,
add sufficient water to produce l00 ml.

Complies
with the following test.

SENSITIVITY - A mlxture 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 colour of the solution to reddish violet.

Phenol Red Reagent:

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: Of the Indian
Pharmacopoeia.

Phenolphthalein Solution: A 1.0 per cent
w/v solution of phenolphthalein in ethanol (95 per cent).

Phenolphthalein Solution, Dilute:
Dissolve 0.1 g of phenolphthalein in 80 ml of ethanol (95 per
cent) and add sufficient water to produce 100 m!.

Complies
with the following test.

SENSITIVITY - A mlxture of 0.1 ml of the
solution and 100 ml of carbon dioxide-free water is colourless.
Not more than 0.2 ml of 0.02 M sodium hydroxide is required to change
the colour to pink.

Phenolphthalein-Thymol Blue
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 per cent) 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 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 examlnation; a yellow colour is
produced. Add 0.15 ml of a 0.5 per cent w/v solution of cupric sulphate; the colour
changes to violet.

Quinaldine Red; 2-(4-Dimethylamlnostyryl) quinoline Ethiodide:
C₂₁H₂₃IN₂= 430.33

When used for
the non-aqueous titration in anhydrous glacial acetic acid, the colour changes from magenta (basic) to almost colourless (acidic).

Quinaldine Red Solution:
A 0.1 per cent w/v solution of quinaldine
red in methanol.

Ruthenium Red; Ammoniated Ruthenium Oxychloride:
H12Cl2N1402Ru3,4H20 = 858.42

Mlcroscopical
staining grade of commerce.

Brownish
red powder.

Ruthenium Red Solution: Dissolve 8 mg
of ruthenium red in

10
ml of lead acetate solution.

Sudan Red G; CI 12150; Sudan Red I;
1-(2'-Methoxyphenylazo)-2-naphthol; C₁₇H_I4N₄O=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 fll of a 0.1 per cent w/v solution
in dichloromethane. After removal of the plate, allow it to dry
in air. The chromatogram shows only one spot.

Thymol Blue; Thymolsulphonphthalein;
4,4' -(3H)-2, 1Benzoxathiol-3-ylidene) dithymol S,S-dioxide: C₂₇H₃₀O₅S
=466.60

Brownish green,
crystalline powder; soluble in ethanol (95 per cent) and in dilute
alkali solutions; slightly soluble in water.

Thymol Blue Solution:
Dissolve 0.1 g of thymol blue in 2.15
ml of 0.1 M sodium hydroxide and 20 ml of ethanol (95 per
cent). After solution is effected, add sufficient water
to produce 100 ml.

Complies
with the following test.

SENSITIVITY - A mlxture of 0.1 ml ofthe solution and 100 ml of carbon dioxidejree
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 colour to yellow.

Thymol Blue Solution, Ethanolic: Dissolve 0.1 g of thymol blue in 100 ml of ethanol (95 per
cent) and filter, if necessary.

Thymolphthalein; 3,3-Bis(
4-hydroxy-5-isopropyl- 2mehtylphenyl)phthalide:
C₂₈H₃₀O₄=430.55

White to
slightly yellow crystalline powder; soluble in ethanol (95 per cent) and
in solutions of alkali hydroxides; insoluble in water.

Thymolphthalein Solution:
A 0.1 per cent w/v solution of thymolphthalein
in ethanol (95 per cent).

Complies
with the following test.

SENSITIVITY - A mlxture of 0.05 ml and 100 ml of
carbon dioxide-free water is colourless. Not
more than 0.05 ml of

0.1
M sodium hydroxide is required to change the colour to blue.

Titan Yellow; CI 19540; Thiazol
Yellow; Sodium 2,2[(diazoamlno
)di-p-phenylene] bis(6-methylbenzothiazole-7sulphonate):
C₂₈H_I9N₅Na₂O₆S₄=
695.71

Yellowish
brown powder.

Titan Yellow Solution: A 0.05 per
cent w/v solution of titan yellow.

Complies
with the following test.

SENSITIVITY -
Add 0.1 ml to a mlxture of
10ml of water, 0.2 ml of a 0.0101 per cent w/v solution of magnesium sulphate and 1.0 ml of 1 M sodium hydroxide; a
pink colour is produced.

Xylene Cyanol
FF: C142135

Blue,
ethanol-soluble dye used as a screening agent in methyl orange-xylene cyanol FF solution.

Xylenol Orange; [3H-2,1-Benzoxathiol-3-ylidenebis-(6hydroxy-
5-methyl-m-pheny lene )methylenenitrilo
]tetra acetic acid S,S-dioxide Tetrasodium Salt:
C_3IH₂₈N₂NH₂O_I3S=760.60

General
laboratory reagent grade of commerce.

Reddish brown,
crystalline powder; gives a violet colour 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 Mlxture;
Xylenol Orange Triturate:
Triturate

1 part of xylenol orange with 99 parts of potassium
nitrate.

Complies
with the following test.

SENSITIVITY -
Add 50 mg to a mlxture of 50
ml of water, 1 ml of 2 M acetic acid and 0.05 ml of lead
nitrate solution. Add sufficient hexamlne
to change the colour from yellow to violet red.
Add 0.1 ml of 0.1 M disodium edetate;
the colour changes to yellow.

Xylenol Orange Solution:
Mlx 0.1 g of xylenol
orange with 100 ml of water and filter, if necessar