Chromium spectrophotometric determination

Spectrophotometric determinations - continued D. or concn. of potassium nitrate, 710 D. of simultaneous, chromium and manganese, 712... 

Diphenylcarbazone and diphenylcarbazide have been widely used for the spectrophotometric determination of chromium [ 190]. Crm reacts with diphenylcarbazone whereas CrVI reacts (probably via a redox reaction combined with complexation) with diphenylcarbazide [ 191 ]. Although speciation would seem a likely prospect with such reactions, commercial diphenylcarbazone is a complex mixture of several components, including diphenylcarbazide, diphenylcarbazone, phenylsemicarbazide, and diphenylcarbadiazone, with no stoichiometric relationship between the diphenylcarbazone and diphenylcarbazide [192]. As a consequence, use of diphenylcarbazone to chelate Crm selectively also results in the sequestration of some CrVI. Total chromium can be determined with diphenylcarbazone following reduction of all chromium to Crm. 

Manzoori JL, Sorouraddin MH, Shemiran F. 1996. Preconcentration and spectrophotometric determination of chromium(VI) and total chromium in drinking water by the sorption of chromium diphenylcarbazone with surfactant coated alumnia. Anal Lett 29 2007-2014. 

Ganescu et al. used thiocyanato Cr(III)-complexes in the titrimetric and spectrophotometric determination of dipyridamole [16]. For titrimetric analysis of the drug (1.36-27.2 mg), sample solutions (25-50 mL) were acidified with hydrochloric acid and treated with excess of a 3% solution of ammonium dianilinetetrakis (thiocyanato) chromium (III) in aqueous 25% ethanol. The red-violet precipitate was collected and washed, decomposed with NaOH, and the mixture again acidified. The liberated thiocyanate was titrated with potassium permanganate, potassium bromate, or potassium iodate. 

The chromium(III-EDTA complex has been extracted by a solution of Aliquat-336 in non-polar solvents before the spectrophotometric determination [30]. 

Chromotropic acid was applied as a reagent for ultraviolet spectrophotometric determination of hexavalent chromium in water [10]. 

Chromium(vi). This inorganic pollutant can be determined by a whole range of analytical techniques, e.g. FAAS, ICP-AES/MS or XRF. However, in this situation the requirement is to determine a particular oxidation state of chromium. While not mentioned specifically in the list of analytical techniques above, a method does exist for the spectrophotometric determination of hexavalent chromium based on extraction with a chelating agent (see Chapter 5 for details). 

C. Pasquini, W.A. Oliveira, Monosegmented system for continuous-flow analysis. Spectrophotometric determination of chromium(VI), ammonia, and phosphorus, Anal. Chem. 57 (1985) 2575. 

Spectrophotometric determination of the extractable content of chromium, lead, nickel and zinc in sewage sludges. A similar strategy to the above-mentioned [355] was used but different standard solution streams were involved. Matrix effects were successfully overcome [356],... 

Y.-Y. Luo, S. Nakano, D.A. Holman, J. Ruzicka, G.D. Christian, Sequential injection wetting film extraction applied to the spectrophotometric determination of chro-mium(VI) and chromium(III) in water, Talanta 44 (1997) 1563. 

EXPERIMENT 25 SPECTROPHOTOMETRIC DETERMINATION OF MANGANESE AND CHROMIUM IN MIXTURE... 

Two-line and multiline manifolds are, of course, now commonplace for FIA methods. In fact, most of the procedures described in the FIA literature (Chapter 7) utilize this approach. Thus, in Ref. 52 is described a turbidimetric procedure for the determination of ammonia in low concentrations with the use of Nessler s reagent, while Ref. 253 recounts the spectrophotometric determination of chromium(VI). Besides being based on one-phase equilibria, multiline manifolds may also involve gas diffusion, solvent extraction, and liquid-liquid phase reactions in packed reactors (see the following sections). It should be emphasized, however, that a FIA system should always be kept as simple as possible, and that a well-designed chemical analysis will often require only the use of a two-line manifold. 

J. C. de Andrade, J. C. Rocha, C. Pasquini, and N. Baccan, Effect of On-Line Complex Formation Kinetics on the Flow Injection Analysis Signal. The Spectrophotometric Determination of Chromium(VI). Analyst, 108 (1983) 621. 

HCrO ] has been shown to be the photo-active species in the photochemical reaction of dilute solutions of chromium(vi) oxyacids with alcoholic reducing agents. The association of chromate with Np , Th, and Fe" in perchlorate solution has been studied spectrophotometrically and the respective formation constants, 63.6,4.70, and 1.93, have been determined. The greater stability of the Np complex has been interpreted in terms of the limited donation of 5/-electron density from Np to the d-orbitals of chromium in the chromate ion. ... 

The absorption spectrum and first formation constant of [Cr(bipy)]2+ have been determined spectrophotometrically in hexamethylphosphoramide (HMPA) (see also Table 39). Since log Ki (4.61) is slightly larger in HMPA than in water, it is said that [Cr(bipy)(HMPA)2]2+ is tetrahedral, although from the general chemistry of chromium(Q) the ion would be expetrted to be in planar or distorted octahedral coordination.52... 

Salama et al. [34] developed and validated a spectrophotometric method for the determination of omeprazole and pantoprazole sodium via their metal chelates. The procedures were based on the formation of 2 1 chelates of both drugs with different metal ions. The colored chelates of omeprazole in ethanol were determined spectrophotometrically at 411, 339, and 523 ran using iron(III), chromium(III), and cobalt(II), respectively. Regression analysis of Beer s plots showed good correlation in the concentration ranges 15-95, 10-60, and 15-150 /ig/ ml of pure omeprazole using iron(III), chromium(III), and cobalt(II), respectively. 

Colour systems suitable for use in the spectrophotometric method may also be formed in redox reactions. Some examples of such reactions are the oxidation of Mn(II) to Mn04" or Cr(III) to Cr04, oxidation of dimethylnaphthidine with vanadium(V) or chromium(VI), oxidation of o-tolidine with cerium(lV) or with chlorine. Examples of oxidation reactions are also the iodide methods, in which iodide ions are oxidized with bromine to give iodate ions which, in turn, react with the excess of iodide anions to form free iodine (see Chapter 25). A colour effect of reduction also occurs, for example, in determinations of Se and Te in the form of coloured sols produced in the reduction of Se(lV) or Te(IV) to their elementary forms. 

The thiocyanate method has been used for determining cobalt in vitamin B12 [94], steel [24,94], and nickel [25]. Cobalt present in considerable amounts in alloys with aluminium, nickel, chromium, manganese, copper, and iron was determined by the differential spectrophotometric analysis [95]. 

Figure 4.67. Manifolds designed for speciation analysis of Cr(VI) and Cr(III) by reversed FI A, both species being determined spectrophotometrically by a single detector, (a) Asynchronous merging zones mode for simultaneous determination of both species, (b) Sequential method for this speciation by use of a selecting valve for determination of Cr(VI) (channel 1) or overall chromium (channel 2). (From Ref. 968, by permission of Springer Verlag.)...

Inorganic ions in biological systems can be quantified by spectrophotometric methods provided they are present at suitable concentrations (of a few micrograms per milliliter or higher) and other species in the medium exhibit little or no absorption. However, many elements including aluminum, cadmium, chromium, and nickel usually cannot be determined by UV-visible spectrophotometry, because they occur at very low concentrations in biological systems. 

The advantage of discrete analyzers is that sample crossover in the system itself is the lowest possible. Volumes of 75 pi of reagent and sample volumes as large as 100 pi are sufficient. In an automated system with a throughput of 200 determinations per hour in the same sample 6 to 10 components (such as ammonium, alkalinity, aluminum, boron, bromide, calcium, chloride, chromium(VI), cyanide, fluoride, iron, magnesium, nitrate, nitrite, phosphate, etc.) can be determined. In discrete analyzers normally conventional spectrophotometric methods are used. These methods are prone to interference of the matrix of the sample. As a good concept for interference studies still is not available, interferences are as yet not sufficiently studied systematically even for routine analyses. 

FIGURE 1,6 Example of manifolds developed for flow injection speciation analysis, (a) Manifold of the reversed FIA system for speciation of chromium with pH measurements and spectrophotometric detection, q—peristaltic pumps, V—injection valves, L— reaction coil, M.E.—pH glass electrode. (Adapted from Ruz, J. et al. 1986. J. Autom. Ghent. 8 70-74.) (b) Manifold of branched FIA system for simultaneous biamperomet-ric determination of nitrate and nitrite. (Cd)Cu—reductive column with copperized cadmium, L—mixing coils. (Adapted from Trojanowicz, M., W. Matuszewski, and B. Szostek. 1992. Anal. Chim. Acta 261 391-398.) (c) Example signal recordings obtained in the FIA system shown in (b) 1-6—standard solutions, A-I—natural water samples. Concentration in standard solutions 1—0.075 2—0.050 3—0.025 mM nitrate and 4—7.5 5—5.0 6—2.5 pM nitrite. 

Traces of chromium in polyolefins originating from Phillips type polymerization catalysts have been determined by spectrophotometric, atomic... 

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