Calcon

Calcon carboxylic acid [3-hydroxy-4-(2-hydroxy-4-sulfo-l-napbtbylazo)napbtbalene-2-carboxylic acid] [3737-95-9] M 428.4, m 300°, X,max 560nm, pKj 1.2, pK2 3.8, PK3 9.26, PK4 13.14. Purified through its p-toluidinium salt. The dye was dissolved in warm 20% aq MeOH and treated with p-toluidine to ppte the salt after cooling. Finally recrystd from hot water. [Itoh and Ueno Analyst (London) 95 583 1970.] Patton and Reeder (Anal Chem 28 1026 1956) indicator and complexes with Ca in presence of Mg and other metal ions. 

Eriochrome Blue Black R (Palatine Chrome Black 6BN, Calcon, 3-hydroxy-4-(2-hydroxy-l-naphthylazo)naphthalene-l-sulfonic acid Na salt] [2538-85-4] M 416.4, pK2 7.0, pKj 13,5. Freed from metallic impurities by three pptns from aqueous soln by addn of HCl. The ppted dye was dried at 60° under vacuum. Indicator for complexometry of Al, Fe and 7i. 

Solochrome dark blue or calcon ( C.1.15705). This is sometimes referred to as eriochrome blue black RC it is in fact sodium l-(2-hydroxy-l-naphthylazo)-2-naphthol-4-sulphonate. The dyestuff has two ionisable phenolic hydrogen atoms the protons ionise stepwise with pK values of 7.4 and 13.5 respectively. An important application of the indicator is in the complexometric titration of calcium in the presence of magnesium this must be carried out at a pH of about 12.3 (obtained, for example, with a diethylamine buffer 5 mL for every 100 mL of solution) in order to avoid the interference of magnesium. Under these conditions magnesium is precipitated quantitatively as the hydroxide. The colour change is from pink to pure blue. 

The titration with EDTA, using solochrome black as indicator, will yield the calcium content of the sample (if no magnesium is present) or the total calcium and magnesium content if both metals are present. To determine the individual elements, calcium may be evaluated by titration using a suitable indicator, e.g., Patton and Reeder s indicator or calcon — see Sections 10.48 and 10.60, or by titration with EGTA using zincon as indicator — see Section 10.61. The difference between the two titrations is a measure of the magnesium content. 

Calcon may also be used for the titration of calcium in the presence of magnesium (compare Section 10.48). The neutral solution (say, 50 mL)is treated with 5 mL of diethylamine (giving a pH of about 12.5, which is sufficiently high to precipitate the magnesium quantitatively as the hydroxide) and four drops... 

The calcium content may then be determined by titration wth EDTA using either Patton and Reeder s indicator or calcon (Section 10.60), or alternatively by titration with EGTA (see Section 10.61). 

Calcium, D. of - continued in limestone or dolomite, (fl) 813 in presence of barium, (ti) 333 with CDTA, (ti) 333 with lead by EDTA, (ti) 333 with magnesium by EDTA, 328 by EGTA, (ti) 331 by flame emission, (aa) 804 Calcium oxalate, thermal analysis 498 Calcon 318 Calculators 133 Calibration of apparatus, 87 of burettes, 88 of graduated flasks, 88 of pipettes, 88 of weights, 74... 

Materials Required Calcium chloride dihydrate 0.15 g dilute hydrochloric acid (10% w/w of HC1) 3.0 ml 0.05 M disodium edetate sodium hydroxide solution (20% w/v in water) calcon mixture (a mixture of 1 part of calcon with 99 parts of freshly ignited anhydrous Na C ) 0.1 g. 

Procedure Weigh accurately about 0.15 g of calcium chloride dihydrate and dissolve it in 50 ml of DW. Titrate with 0.05 M disodium ethylenediamine tetracetate to within a few ml of the expected end point, add 8.0 ml of sodium hydroxide solution and 0.1 g of calcon mixture and continue the titration until the colour of the solution changes from pink to a full blue colour. Each ml of 0.05 M disodium ethylene disodium tetracetate is equivalent to 0.007351 g of CaCl2.2H20. 

Calcium carbonate 0.1 g Calcon mixture Each ml of 0.05 M disodium edetate ee 0.005004 g of CaC03... 

Calcon carboxylic acid [3737-95-9] M 428.4, m 300". Purified through its p-toluidinium salt. The dye was dissolved in warm 20% aq MeOH and treated with p-toluidine to ppte the salt after cooling. Finally recrystd from hot water. [Itoh and Ueno Analyst 95 583 1970]. 

More than 50 such dyestuffs have been proposed as indicators,8 but they have in common at least one o-hydroxy group from which the titratable metal displaces a hydrogen atom and forms a five-membered chelate ring with the azo nitrogens (cf 51) most have two o-hydroxy groups and can form two chelate rings. Of the few that are still used calcon (eriochrome blue black R ... 

Calcon carboxylic acid [3>hydroxy-4-(2-hydroxy-4-sulfo-l-naphthylazo)naphthalene-2-carboxylic acid] [3737-95-9] M 428.4, m 300°, Xmax 560nm, pKi 1.2, pK2 3.8, pKs 9.26,... 

Hoachat Cal Calcon M2S 3.2 mm bars Hoechsi Cal. Calcon M270 3.2 mm bars Hoechst Cel. Catcon M90 3.2 mm bars... 

Hoechsi Dal. Calcon M25 3.2 mm bars Hoechsi Cai- Celcon M270 3-2 mm bars BASF Ultreform... 

Some of the metal ion indicators used for calcium and magnesium are discussed below Solochrome dark blue or calcon... 

Calcon indicator Dissolve 0.20 g of the dyestuff (calcon) in 50 cc methanol (ethanol may also be used). Prepare fresh solution weekly. 

Add 10-12 drops of calcon indicator stir the solution and titrate with standard EDTA solution until the colour changes from pink to pure blue. 

Standardise the EDTA solution with standard Ca solution using Eriochrome black-T indicator or calcon indicator (see note below), using the procedure for calcium-estimation. 

If the EDTA solution is prepared by dissolving 2.0 g of the salt in one litre water without addition of 0.05 g magnesium chloride hexahydrate, then use calcon indicator during standardization of EDTA with standard calcium solution. 

Determine a blank for KCl-triethanolamine solution using Eriochrome black T and calcon indicators. 

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