Eriochrome black T indicator

Although the most sensitive line for cadmium in the arc or spark spectmm is at 228.8 nm, the line at 326.1 nm is more convenient to use for spectroscopic detection. The limit of detection at this wavelength amounts to 0.001% cadmium with ordinary techniques and 0.00001% using specialized methods. Determination in concentrations up to 10% is accompHshed by solubilization of the sample followed by atomic absorption measurement. The range can be extended to still higher cadmium levels provided that a relative error of 0.5% is acceptable. Another quantitative analysis method is by titration at pH 10 with a standard solution of ethylenediarninetetraacetic acid (EDTA) and Eriochrome Black T indicator. Zinc interferes and therefore must first be removed. 

Porter, J. D. A stable form of eriochrome black T indicator. Chemist-... 

Solution of Eriochrome Black T Indicator. Dissolve 0.5 g of a chemically pure preparation in 10 ml of the bufier solution and add ethanol up to 100 ml. Other oxynitrodyes can be used in addition to Eriochrome black T. 

Magnesium Nitrate may be detd by a gravimetric method, weighing Mg PgOf as the final product or by titrating an aliquot of the water extract with EDTA (Ethylenediamine-tetracetic Acid) at a pH of ca 10 using Eriochrome Black T indicator. This method is described in Ref 17, D90-5d, pi5... 

Back titration prevents precipitation of analyte. For example, Al(OH)3 precipitates at pH 7 in the absence of EDTA. An acidic solution of Al3+ can be treated with excess EDTA, adjusted to pH 7-8 with sodium acetate, and boiled to ensure complete formation of stable, soluble Al(EDTA)-. The solution is then cooled, Eriochrome black T indicator is added, and back titration with standard Zn2+ is performed. 

Color Plate 7 Titration of Mg2+ by EDTA, Using Eriochrome Black T Indicator (Demonstration 12-1)... 

Assay Transfer about 350 mg of sample, accurately weighed, into a 250-mL beaker. Add 100 mL of water and 1 mL of hydrochloric acid. While stirring constantly, heat to approximately 75° to 80° on a hot plate. Add 25 mL of 0.05 M disodium EDTA, and if necessary, adjust the pH to 10.0 0.2 with 1 N NaOH. Add 10 mL of ammonia-ammonium chloride buffer TS and approximately 8 drops of eriochrome black T indicator solution. Continue titrating with 0.05 M disodium EDTA until a true blue endpoint is reached and holds for at least 3 min. Each milliliter of 0.05 M disodium EDTA is equivalent to 9.05 mg of MnslCgHsOy. ... 

Alkaline Earths. 1.0 M stock solutions of the alkaline earth metal chlorides were prepared by dissolving the chloride salt in D2O (99.9% D). Standardization was either by direct EDTA titration (for CaCl2) or back titration of the metal-EDTA complex with standard M (C104)2 using Eriochrome Black T indicator. The solutions were buffered to pH 10 with NH3/NH4CI and the determinations were done in triplicate. 

Traces of many metals interfere in the determination of calcium and magnesium using Eriochrome Black T indicator e.g. Co, Ni, Cu, Zn, Hg and Mn. The interference can be overcome by addition of a little hydroxylamine hydrochloride which reduces some of the metals to their lower valency states and also of sodium or potassium cyanide complexes. Iron may also be rendered harmless by addition of a little sodium sulphide. 

Eriochrome Black T indicator Take 100 ml of ethanol and dissolve 4.5 g hydroxylamine hydrochloride in it. Now add 0.5 g of the indicator and prepare solution. 

Add 10 ml of NH Cl-NH OH buffer, (2-3 carbamate crystals if required) and 3-4 drops of Eriochrome Black T indicator. 

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. 

Why is a small amount of magnesium salt added to the EDTA solution used for the titration of calcium with an Eriochrome Black T indicator ... 

Water hardness, due to Ca " and Mg, is expressed as mg/L CaCOs (ppm). The total of Ca " " and Mg is titrated with standard EDTA using an Eriochrome Black T indicator. A standard EDTA solution is prepared from dried (do not exceed 80°C) Na2H2Y 2H2O (purity 100.0 0.5%). If the sample does not contain magnesium, Mg-EDTA is added to the titration flask to provide a sharp end point with the Erio-chrome Black T, since calcium does not form a sufficiently strong chelate with the indicator to give a sharp end point. See the discussion in Chapter 9 for a more complete description. 

Provided. 0.5% (wt/vol) Eriochrome Black T indicator solution in ethanol,... 

As EDTA is added it displaces the cations from the cation-indicator complex by forming more stable complexes with the cations. When all of the Ca and Mg is complexed with EDTA, (at the end point), the solution turns from wine-red to blue due to the free Eriochrome Black T indicator. In order to obtain a sharp end point, a small amount of magnesium ions must be present. This is generally not a problem with natural water samples, which tend to contain some Mg, but it is a problem when standardizing EDTA solutions with pure CaC03. A small quantity of MgCl2 is added to the standard EDTA solution to ensure the presence of Mg ions. 

Reagents. Poly(vinyl alcohol) (100 % hydrolyzed) with average molecular weight 14,000, cyanuric chloride (97%), fluoresceinamine isomer I and eriochrome black T (indicator grade) were purchased from Aldrich Chemical Co. Glutaraldehyde solution (50% (w/w) was obtained from Fisher Scientific. 

Lime plus magnesia. Titrimetrically with EDTA in triethanolamine and ammonia using methylthymol blue indicator. For chrome-bearing samples, a cleanup through an ion-exchange resin is required first followed by EDTA titrimetry with an Eriochrome Black T indicator. 

Calmagite Dissolve 0.05 g of indicator in 100 mL of water. Alternatively, dissolve 0.1 g Eriochrome black T indicator in 7.5 mL of triethanolamine plus 2.5 mL of absolute ethanol. Color changes are the same for both indicators. 

Pipet out 10 ml of standard hard water into a conical flask. Add to it 40 ml distilled water with a measuring cylinder, 2 ml of buffer solution and 2 drops of Eriochrome black T indicator. A wine red colour appears. Titrate against EDTA solution, taken in the burette, to a colour change from wine red to pure blue. Record the volume of EDTA used as A ml. Take three coitcordant readings. 

What is the effect on the end-point with Eriochrome black-T indicator if tlie hard water sample does not contain Mg ... 

Since a suitable indicator is not always available for the direct titration against EDTA, a back titration is recommended (Sec.2.2.4) where a known excess of standard EDTA solution is added to an aliquot of the nickel solution, back titrating the excess against standard ZnS04 solution. To 25.00 cm of 0.1 M Ni(ll) solution, add a known excess (50.00 cm ) of the standardised O.l.M. EDTA solution in a 400 cm conical flask. Dilute the solution to about 200 cm and add 4 cm of the buffer solution (pH = 10) and 1-2 drops of Eriochrome Black T indicator. Titrate the excess of EDTA with standard 0.1 M zinc sulphate solution until the colour changes sharply from blue to greenish red. Repeat to obtain concordant results. Calculate, from the average titre, the concentration of nickel(II) in g dm ... 

---