A database about Preparation of Laboratory Reagents. A Project of SCIENCE Pakistan

EDTA Indicators

Bromopyrogallol Red
Dibromopyrogallol sulphone phthalein (VIII)

Dissolve 0.05g of the reagent in 100ml. of 50% ethanol.
The indicator is coloured orange-yellow in strongly acid solutions,; claret red in nearly neutral solutions; and violet to blue in basic solutions.
Calcon or Solochrome Dark Blue
sodium 1-(2- hydroxy-1-naphthylazo)-2-naphthol-4-sulphonate, Colour I ndex No.202; also called  
Eriochrome Blue Black R.
Dissolve 0.2g of the dyestuff in 50ml. of methanol.
The colour change is from pink to pure blue.
1-(1-hydroxy-4-methyl-2-phenylazo)-2-naphthol-4-sulphonic acid (IX)
Can be substituted for Eriochrome Black T without change in the experimental procedures for calcium and magnesium.It has same colour change, which is clearer and sharper, and aqueous solutions of the indicator are almost stable indefinitely.
Dissolve 0.05g of calmagiite in 100ml. of water. The indicator is stable for at least 12 months when stored in a polythene bottle and in the dark.
Eriochrome Bkack T
Sodium 1-(1-hydroxy-2-naphthalyzo)-6-nitro-2-naphthol-4-sulphonate (1); also known as Solochrome Black T or WDFA or No. 2 in the Colour Index. Not recommended for titration of solutions more acidic than Ph 6.5.
Dissolve 0.2 g of the dyestuff in 15ml. of ethanolamine and add 5ml of absolute ethanol to reduce the viscosity; the reagent is stable for several months.
A 0.4% solution of the pure dye in methanol may last for about a month.
Colour change is from blue to red.
Eriochrome Red B
sodium salt of 4-(2-hydroxy-4-sulpho-1-naphthylazo)-3-methyl-1-phenyl-2-pyrazolin-5-one (IX)---a pyrazolone azo-B-naphthol dyestuff.
Dissolve 0.1g of the dyestuff in 50ml, ethanol. It is stable indefinitely.
The colour change from pink to pale yellow is almost instantaneous at about 80oC.
Fast Sulphon Black F
Sodium salt of 1-hydrovy-8-(2-hydroxynaphthylazo)-2-(solphonaphtylazo)-3,6-disulphonic acid (V)
The indicator solution is 0.5% solution in water.
Specific colour change for copper is from magenta to pale blue to bright green.
See Patton and Reeder's
This is the Ammonium salt of purpuric acid.
Suspend 0.5g of the powdered dyestuff in water, shake thoroughly and allow to settle. The saturated supernatant is used as the indicator.
The colour change is towards a blue endpoint.
Patton and Reeders indicator
2-hydroxy-1-(2-hydroxy-4-sulpho-1-naphthylazo)-3-naphthoic acid (111)
Also known by the abbreviated name HHSNNA.
The dyestuff is thoroughly mixed with 100 times its weight of sodium sulphate, and 1g of this mix is used for each titration.
Used in the direct titration of calcium, particularly in the presence of magnesium, pH range 12-14.
A sharp colour change is obtained from wine red to pure blue.
Pyrocatechol Violet
Pyrocatechol sulphone phthalein (VII); Catechol violet.

Dissolve 0.1g of the dyestuyy in 100ml.of water. This solution is stable for several weeks.
Colour change is progressive, from yellow yo blue to green.
Thymolphthalein complexone

3,3-bis-[n,n-(carboxymethyl)aminomethyl] thymolphthalein (X)
Prepare a 0.5% solution in ethanol.alternatively, a finely ground mixture 1:100 with AR potassium nitrate may be used.
Blue to colourless or slight pink in alkaline medium.
Variamine Blue B
The indicator solution is a 1% solution of the base in water. Ferric complex with EDTA - sharp change in redox potential - colourless to violet blue complex.
Xylenol Orange
3,3-bis[NN-di-(carboxymethyl)-aminomethyl]-o-cresolsulphonephthalein (VI
Dissolve 0.5g of xylenol orange indicator in 100ml. of water) The solution is stable indeffinitely.
Acid solutions are coloured lemon yellow and those of the metal complexes intensely red.
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