EDTA titrations photometric

The method described here is based on the difference between measurements of total alkaline earths by complexometric titration with EDTA (ethylenediamine-N,N,N, N -tetra-acetic acid) and selective measurement of calcium described in Section 11.2.1. The simultaneous EDTA titration of calcium, strontium and magnesium involves Eriochrome Black T (EBT) as indicator and was originally applied to seawater analysis by Voipio (1959) and Pate and Robinson (1961). To eliminate subjective errors in the determination of the endpoint, Culkin and Cox (1966) used photometric endpoint detection. A slight modification of this procedure, including the standardization of EDTA by magnesium is reported here. 

We must also keep in mind that equivalence points of EDTA titrations can be detected by using several instrumental methods. A first method, potentiometry, was just mentioned. There are also other potentiometric methods, based on other principles than the previous one, that may be used. Amperometric and conductometric methods have been proposed equally (see electrochemical methods of analysis). Finally, we ll mention photometric and spectrophotometric indications. 

By rxn. of SnCla with BU3AI in (CHaOMe)a-MePh at 50°, in 777. yield (2 +98). Prop.t (Far) IR, assignment (110) and Moessbauer resonance (2230, 2509) spectra. Anal. detn. by 8-ray reflection technique (687), by polarography (2265), by photometric method (I8O6), detn. of BuSnOaH in tech. BuaSnO, by EDTA titration (IOO7). 

Used for extraction-photometric detn. of Ga (CHCI3), Sc (Amax 520 nm, e 15000, Et20) as an aq. soln. as an indicator in complexometric indicator in EDTA titrations (Ca, Mg) photometric detn. of codeine, Nb (Amax 540 nm, e 16000), as 0.1% soln. in Me2CO for extraction-fluorimetric detn. of Al (pH 3.2-5.3, butanol). Orange-red cryst. Sol. H2O, Me2CO, EtOH, CHCI3,... 

Discussion. The titration of a copper ion solution with EDTA may be carried out photometrically at a wavelength of 745 nm. At this wavelength the copper-EDTA complex has a considerably greater molar absorption coefficient than the copper solution alone. The pH of the solution should be about 2.4. 

Discussion. Salicylic acid and iron(III) ions form a deep-coloured complex with a maximum absorption at about 525 nm this complex is used as the basis for the photometric titration of iron(III) ion with standard EDTA solution. At a pH of ca 2.4 the EDTA-iron complex is much more stable (higher stability constant) than the iron-salicylic acid complex. In the titration of an iron-salicylic acid solution with EDTA the iron-salicylic acid colour will therefore gradually disappear as the end point is approached. The spectrophotometric end point at 525 nm is very sharp. 

Determination of iron(III) in the presence of aluminium. Iron(III) (concentration ca 50 mg per 100 mL) can be determined in the presence of up to twice the amount of aluminium by photometric titration with EDTA in the presence of 5-sulphosalicylic acid (2 per cent aqueous solution) as indicator at pH 1.0 at a wavelength of 510 nm. The pH of a strongly acidic solution may be adjusted to the desired value with a concentrated solution of sodium acetate about 8-10 drops of the indicator solution are required. The spectrophotometric titration curve is of the form shown in Fig. 17.23. 

Jagner and Kerstein [654,655] used computer-controlled high-precision complexiometric titration for the determination of the total alkaline earth metal concentration in seawater. Total alkaline earths were determined by photometric titration using EDTA with eriochrome Black as indicator. The method yielded 63.32 (xmolekg-1 for the total alkaline earth concentration in standard seawater of 3.5% salinity. The precision was about 0.01%. 

Calibration solutions of cadmium and lead have been prepared from high purity (higher than 98%) cadmium and lead nitrate dissolved in nitric acid. A high accuracy titration method (EDTA complexometry reaction with photometric detection) was used to determine the final... 

Powder x-ray diffraction (Siemens D-500 diffractometer) and scanning electron microscopy (JEOL, JSM-840) methods were used for characterization of zeolite products. Infrared spectra (Perkin Elmer 783 infrared spectrophotometer) were used for investigation of nucleation gel. The amount of Si, Al, Na in zeolite products was analysed by conventional analytical method, i.e. gravimetric for Si, gravimetric and volumetric methods (titration by EDTA) for Al and flame photometric method for Na. The WL value in Table 1 was used to estimate the amount of water and organic species in an as-synthesized zeolite product. 

Macro quantities of selenium can be determined gravimetrically after reduction to the elemental form by various reagents such as tin (II) chloride, potassium iodide, or ascorbic acid (I). Ooba described a technique whereby the element is precipitated from perchloric acid solution with hydrazine (2). Selenium may be titrated with standard solutions of sodium thiosulfate, iodide, and ferrous, chromous, or trivalent titanium salts after oxidation to Se(VI) (I). Photometric and fluorometric methods based on formation of the piaselenol with diaminobenzidine or 2,3-diaminonaphthalene has been used for the determination of selenium (I, 3,4,5). Interfering elements such as As, Co, Cr, Cu, Fe, Hg, and Ni, are masked with EDTA or other chelating agents. 

FIGURE 14-13 Photometric titration curves (a) tola hardness of water, (b) determination of sulfate. In (a), total water hardness is obtained by titration with 0.10 M EDTA at 610 nm lor 100 ml of a solution that contained 2.82 mmol/L total hardness. Eriochrome Black T was the indicator, fn (b). 10.0 ml of a solution containing sulfale was titrated with 0.050 M BaCI using Thorin as an indicator and a wavelength of 523 nm. The response shown is proportional to transmittance. (From A. L, Underwood. Ana/. Chom.. 1954, 26. 1322. Figure t, p. 1323. Copyright 1954 American Chemical Society.)... 

The concentration of iron(III) in solution can also be obtained by titration with EDTA. However, in this case salicylic acid is also added to the titration cell. Iron(III) forms a strongly colored complex with salicylic acid however, the iron-EDTA complex has a much higher stability constant. As the titration is carried out, there is a very sharp disappearance of color at the end-point as the iron-EDTA complex replaces the iron-salicylic acid complex. This titration can be followed photometrically at 525 nm and produces a plot similar to Figure lA. 

The photometric end point has been applied to many types of reactions. For example, most standard oxidizing agents have characteristic absorption spectra and thus produce photometrically detectable end points. Although standard acids or bases do not absorb, the introduction of acid-base indicators permits photometric neutralization titrations. The photometric end point has also been used to great advantage in titrations with EDTA (cthylenediamineietraacelic... 

Sweetser and Bricker determined a variety of cations by spectrophotometric titrations with EDTA. Bruckenstein determined water in acetic acid by an ultraviolet photometric titration. C4 and higher molecular-weight olefins in automobile exhausts have been determined by spectrophotometric titration, using the high molar absorptivity of free tribromide ion at 290 m/x. 

Bismuth(III) compounds in solution can be titrated with EDTA solution or precipitated as orthophosphate or they can be electrolytically determined as Bi. A suitable spectro-photometric method is based on complex formation with iodide. 

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